VCA2615 SBOS316D - JULY 2005 - REVISED OCTOBER 2008 Dual, Low-Noise Variable-Gain Amplifier with Preamp FEATURES DESCRIPTION D VERY LOW NOISE: 0.7nV//Hz D LOW-NOISE PREAMP (LNP) The VCA2615 is a dual-channel, variable gain amplifier consisting of a Low-Noise Preamplifier (LNP) and a VariableGain Amplifier (VGA). This combination along with the device features makes it well-suited for a variety of ultrasound systems. - - - - D Active Termination Programmable Gains: 3, 12, 18, 22dB Programmable Input Impedance (RF) Buffered, Differential Outputs for CW Processing - Excellent Input Signal Handling Capabilities LOW-NOISE VARIABLE-GAIN AMPLIFIER - High/Low-Mode (0/+6dB) - 52dB Gain Control Range - Linear Control Response: 22dB/V - Switchable Differential Inputs - Adjustable Output Clipping-Level BANDWIDTH: 42MHz HARMONIC DISTORTION: -55dB 5V SINGLE SUPPLY The LNP offers a high level of flexibility to adapt to a wide range of systems and probes. The LNP gain can be programmed to one of four settings (3dB, 12dB, 18dB, 22dB), while maintaining excellent noise and signal handling characteristics. The input impedance of the LNP can be controlled by selecting one of the built-in feedback resistors. This active termination allows the user to closely match the LNP to a given source impedance, resulting in optimized overall system noise performance. The differential LNP outputs are provided either as buffered outputs for further CW processing, or fed directly into the variable-gain amplifier (VGA). Alternatively, an external signal can be applied to the differential VGA inputs through a programmable switch. D D D D LOW-POWER: 154mW/Channel D POWER-DOWN MODES Following a linear-in-dB response, the gain of the VGA can be varied over a 52dB range with a 0.2V to 2.5V control voltage common to both channels of the VCA2615. In addition, the overall gain can be switched between a 0dB and +6dB postgain, allowing the user to optimize the output swing of VCA2615 for a variety of high-speed Analog-to-Digital Converters (ADCs). As a means to improve system overload recovery time, the VCA2615 provides an internal clipping function where an externally applied voltage sets the desired clipping level. APPLICATIONS D MEDICAL AND INDUSTRIAL ULTRASOUND D SYSTEMS - Suitable for 10-Bit and 12-Bit Systems TEST EQUIPMENT FB1 FB2 FB3 FB4 LNPOUT- The VCA2615 operates on a single +5V supply and is available in a small QFN-48 (7x7mm) or TQFP package. LNPOUT+ VCAIN+ VCAIN- H/L (0dB or +6dB) Feedback Resistors +1 +1 LNPIN+ VCAOUT+ LNP VGA MUX LNPIN- VCAOUT- (3, 12, 18, 22dB) 52dB Range 1/2 VCA2615 G1 G1 VCAINSEL VCNTL VCLMP Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. Copyright 2005-2008, Texas Instruments Incorporated ! ! www.ti.com " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 ABSOLUTE MAXIMUM RATINGS(1) This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. Power Supply (VDD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6V Analog Inputs . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to (+VS + 0.3V) Logic Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to (+VS + 0.3V) Case Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +100C Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +150C Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . -40C to +150C ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. (1) Stresses above those listed under Absolute Maximum Ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may affect device reliability. PACKAGE/ORDERING INFORMATION(1) PRODUCT PACKAGE-LEAD PACKAGE DESIGNATOR SPECIFIED TEMPERATURE RANGE PACKAGE MARKING QFN-48 RGZ -40C to +85C VCA2615 TQFP-48 PFB -40C to +85C VCA2615 ORDERING NUMBER TRANSPORT MEDIA, QUANTITY VCA2615RGZR Tape and Reel, 2500 VCA2615RGZT Tape and Reel, 250 VCA2615PFBR Tape and Reel, 1000 VCA2615PFBT Tape and Reel, 250 VCA2615 (1) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI website at www.ti.com. FUNCTIONAL BLOCK DIAGRAM LNP OUT- A VC A IN- A LNP O UT+A V CA IN +A Buffe r VC A OUT+A INP UT A Buffer LN P VGA VC A OUT- A C EXTA1 Ga in Co ntrol Logic C EXTA2 Fee db ack Network F B1 F B2 VC A INSEL F B3 F B4 G1 G2 Ga in Co ntrol Logic Fee db ack Network C EXTB1 C EXTB2 VC A OUT- B VGA LN P Buffer INP UT B VC A OUT+B B uffer LNP OUT- B 2 VC A IN- B LN P OUT+B V CA IN +B H /L V CLMP V CNTL " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 ELECTRICAL CHARACTERISTICS All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. VCA2615 PARAMETER CONDITIONS MIN TYP MAX UNIT PREAMPLIFIER (LNP and Buffer) Input Resistance, RIN Input Resistance Input Capacitance Maximum Input Voltage See Note(1) 100 45 2.3 0.78 0.39 0.23 5 0.8 1 50 -55 -55 0.1 k k pF VPP VPP VPP VPP VPP nV/Hz pA/Hz MHz dBc dBc s RL > = 500 3.3 1.85 60 3 VPP V mA FB (1-4) = 0111 FB (1-4) = 1011 FB (1-4) = 1101 FB (1-4) = 1110 FB (1-4) = 0000 1500 1000 500 250 130 Linear Operation(2), VCNTL = 0.7V 2 50 -60 -63 100 VPP MHz dBc dBc V/s 0.7 0.25 to 2.6 50 3 60 -44 -70 1 25 100 80 6 2.5 -55 -55 42 nV/Hz V mV mA dBc dBc ns ns pF VPP V dB dB MHz With Active Feedback Termination Feedback Termination Open Maximum Input Voltage Input Voltage Noise Input Current Noise Bandwidth 2nd-Harmonic Distortion 3rd-Harmonic Distortion LNP Gain Change Response Time BUFFER (LNPOUT+A/B, LNPOUT-A/B) Output Signal Range(2) LNP Gain (G1, G2) = 00 - Linear Operation(2) LNP Gain (G1, G2) = 01 - Linear Operation(2) LNP Gain (G1, G2) = 10 - Linear Operation(2) LNP Gain (G1, G2) = 11 - Linear Operation(2) Any LNP Gain - Overload (symmetrical clipping) RS = 0; Includes Buffer Noise, LNP Gain = 11 fIN = 5MHz fIN = 5MHz LNP Gain 00 to 11; to 90% Signal Level Output Common-Mode Voltage Output Short-Circuit Current Output Impedance ACTIVE TERMINATION Feedback Resistance(3), RF VARIABLE-GAIN AMPLIFIER (VGA) Peak Input Voltage Upper -3dB Bandwidth 2nd-Harmonic Distortion 3rd-Harmonic Distortion Slew-Rate VCNTL = 2.5V, 1VPP Differential Output VCNTL = 2.5V, 1VPP Differential Output PREAMPLIFIER AND VARIABLE-GAIN AMPLIFIER (LNP AND VGA) Input Voltage Noise Clipping Voltage Range (VCLMP) Clipping Voltage Variation Output Impedance Output Short-Circuit Current Overload Distortion (2nd-Harmonic) Crosstalk Delay Matching Overload Recovery Time Maximum Output Load Maximum Capacitive Output Loading Maximum Output Signal(2) Output Common-Mode Voltage 2nd-Harmonic Distortion 3rd-Harmonic Distortion Upper -3dB Bandwidth VCLMP = 0.5V, VCAOUT = 1.0VPP fIN = 5MHz, Single-Ended, Either Output VIN = 250mVPP fIN = 5MHz 50 in Series Input Signal = 5MHz, VCNTL = 1V Input Signal = 5MHz, VCNTL = 1V VCNTL = 2.5V -45 -45 (1) RIN + RF (1 ) ALNP 2 ) (2) 2nd-harmonic, 3rd-harmonic distortion less than or equal to -30dBc. (3) See Table 5. (4) Referred to best-fit dB linear curve. (5) Parameters ensured by design; not production tested. (6) Do not leave inputs floating; no internal pull-up/pull-down resistors. 3 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 ELECTRICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. VCA2615 PARAMETER CONDITIONS MIN TYP MAX UNIT ACCURACY Gain Slope Gain Error(4) Gain Range Gain Range Gain Range (H/L) VCNTL = 0.4V to 2.0V VCNTL = 0.4V to 2.0V VCNTL = 0.2V to 2.5V VCNTL = 0.4V to 2.0V H/L = 0 (+6dB); VGA High Gain; VCNTL = 0.2V to 2.5V H/L = 1 (0dB); VGA Low Gain; VCNTL = 0.2V to 2.5V Output Offset Voltage, Differential Channel-to-Channel Gain Matching VCNTL = 0.4V to 2.0V, CHA to CHB 22 0.9 52 36.5 -12 to +40 -18 to +34 50 0.33 VCNTL = 0.2V to 2V; to 90% Signal Level 0.2 to 2.5 1 0.6 -1.5 +1.5 dB/V dB dB dB dB dB mV dB GAIN CONTROL INTERFACE (VCNTL) Input Voltage Range Input Resistance Response Time V M s DIGITAL INPUTS(5), (6) (G1, G2, PDL, PDV, H/L, FB1-FB4, VCAINSEL) VIH, High-Level Input Voltage VIL, Low-Level Input Voltage Input Resistance Input Capacitance 2.0 0.8 1 5 V V M pF POWER SUPPLY Supply Voltage Power-Up Response Time Power-Down Response Time Total Power Dissipation VGA Power-Down LNP Power-Down 4.75 PDV, PDL = 1 PDV = 0, PDL = 1 PDL = 0, PDV = 1 5.0 25 2 308 236 95 5.25 350 V s s mW mW mW THERMAL CHARACTERISTICS Temperature Range Thermal Resistance, qJA qJC qJA Ambient, Operating QFN-48 Soldered Pad; Four-Layer PCB with Thermal Vias TQFP-48 (1) RIN + RF (1 ) ALNP 2 ) (2) 2nd-harmonic, 3rd-harmonic distortion less than or equal to -30dBc. (3) See Table 5. (4) Referred to best-fit dB linear curve. (5) Parameters ensured by design; not production tested. (6) Do not leave inputs floating; no internal pull-up/pull-down resistors. 4 -40 +85 29.1 2.2 58 C C/W C/W C/W " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 FB2 FB1 VCA OUT+B VCA OUT-B GNDB 41 40 39 38 37 VCA INSEL 44 V CNTL FB4 45 FB3 VCA OUT+A 46 42 VCA OUT-A 47 43 GNDA 48 PIN CONFIGURATION V DDB V DDA 1 36 C EXTA1 2 35 CEXTB1 C EXTA2 3 34 CEXTB2 VCA IN- A 4 33 VCA IN-B VCA IN+A 5 32 VCA IN+B LNPOUT- A 6 31 LNP OUT-B LNPOUT+A 7 30 LNP OUT+B NC 8 29 NC VB 9 28 NC VDDAL 10 27 VDDBL GNDAL 11 26 GNDBL LNP IN- A 12 25 LNP IN-B GNDR H/L 20 VCM 24 19 V CLMP PDV 18 V DDR 23 17 22 16 LNP IN+A PDL 15 V DDA LNP IN+B 14 G2 21 13 G1 VCA2615 (Thermal Pad tied to Ground Potential, QFN only) PIN CONFIGURATION PIN 1 DESIGNATOR VDDA 2 3 4 5 6 DESCRIPTION Channel A + Supply PIN 25 DESCRIPTION Channel B LNP Inverting Input 26 DESIGNATOR LNPIN-B GNDBL CEXTA1 CEXTA2 External Capacitor External Capacitor 27 VDDBL VCAIN-A VCAIN+A VDD B Channel LNP Channel A VCA Negative Input 28 NC Do Not Connect Channel A VCA Positive Input 29 NC Do Not Connect Channel A LNP Negative Output 30 Channel B LNP Positive Output Channel A LNP Positive Output 31 LNPOUT+B LNPOUT-B VCAIN+B VCAIN-B Channel B VCA Positive Input CEXTB2 CEXTB1 External Capacitor VDDB GNDB Channel B + Supply Channel B VCA Negative Output 7 LNPOUT-A LNPOUT+A 8 NC Do Not Connect 32 9 VB 0.01F Bypass 33 10 VDDAL VDD A Channel LNP 34 11 GNDAL GND A Channel LNP 35 12 Channel A LNP Inverting Input 36 13 LNPIN-A G1 LNP Gain Setting Pin (MSB) 37 14 G2 LNP Gain Setting Pin (LSB) 38 15 VDDA LNPIN+A Supply Pin for Gain Setting 39 VCAOUT-B VCAOUT+B 16 17 18 19 20 21 GND B Channel LNP Channel B LNP Negative Output Channel B VCA Negative Input External Capacitor Channel B Ground Channel B VCA Positive Output Channel A LNP Noninverting Input 40 FB1 Feedback Control Pin VDDR VCLMP Supply for Internal Reference 41 FB2 Feedback Control Pin VCA Clamp Voltage Setting Pin 42 FB3 Feedback Control Pin VCM GNDR 0.1F Bypass 43 VCA Control Voltage Input Ground for Internal Reference 44 VCNTL VCAINSEL Channel B LNP Noninverting Input 45 FB4 Feedback Control Pin Power Down LNPs 46 Channel A VCA Positive Pin Channel A Ground 22 LNPIN+B PDL 23 PDV Power Down VCAs 47 VCAOUT+A VCAOUT-A 24 H/L VCA High/Low Gain Mode 48 GNDA VCA Input Select, Hi = External Channel A VCA Negative Pin 5 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. GAIN vs VCNTL (Hi VGA Gain) LNP 10 LNP 01 LNP 00 65 60 55 50 45 40 35 30 25 20 15 10 5 0 -5 -10 -15 LNP 11 LNP 10 LNP 01 LNP 00 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 LNP 11 Gain (dB) VCNTL (V) VCNTL (V) Figure 1 Figure 2 GAIN ERROR vs VCNTL (Lo VGA Gain) Gain (dB) 0.5 1.0 0 -0.5 0.5 0 -0.5 -1.0 -1.5 -1.5 -2.0 -2.0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 -1.0 VCNTL (V) VCNTL (V) Figure 3 GAIN ERROR vs VCNTL VCNTL (V) Figure 5 6 VCNTL (V) Figure 6 2.0 1.9 1.8 1.7 1.6 1.5 1.4 -2.0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 -1.5 -40_ C 1.0 1MHz 2MHz 5MHz 10MHz -1.0 0.9 -0.5 0.8 0 +25_C +85_C 0.7 0.5 0.6 Gain Error (dB) Gain Error (dB) 1.0 GAIN ERROR vs VCNTL vs TEMPERATURE 0.5 1.5 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 -1.6 -1.8 -2.0 0.4 2.0 Figure 4 1.3 1.0 LNP 00 LNP 01 LNP 10 LNP 11 1.5 1.2 1.5 Gain (dB) 2.0 LNP 00 LNP 01 LNP 10 LNP 11 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.0 GAIN ERROR vs VCNTL (Hi VGA Gain) 1.1 60 55 50 45 40 35 30 25 20 15 10 5 0 -5 -10 -15 -20 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 Gain (dB) GAIN vs VCNTL (Lo VGA Gain) " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. GAIN MATCHING, CHA to CHB VCNTL = 2.0V 60 50 50 40 40 0.37 0.25 0.31 0.13 0.19 0.07 0.01 -0.05 -0.17 -0.11 -0.23 Delta Gain (dB) Delta Gain (dB) Figure 7 Figure 8 GAIN vs FREQUENCY (VCNTL = 0.7V, Lo VGA Gain) GAIN vs FREQUENCY (VCNTL = 0.7V, Hi VGA Gain) 25 30 20 LNP = 10 LNP = 10 20 Gain (dB) 10 LNP = 11 25 LNP = 11 15 Gain (dB) -0.29 -0.53 0.49 0.35 0.42 0.21 0.28 0.14 0.07 -0.00 -0.07 -0.14 0 -0.28 0 -0.21 10 -0.35 10 -0.42 20 -0.49 20 -0.35 30 -0.41 30 -0.47 Units 60 -0.56 Units GAIN MATCHING, CHA to CHB VCNTL = 0.4V LNP = 01 5 15 LNP = 01 10 0 5 LNP = 00 LNP= 00 -5 0 0.1 60 55 10 100 0.1 45 Figure 9 Figure 10 GAIN vs FREQUENCY (VCNTL = 2.5V, Lo VGA Gain) GAIN vs FREQUENCY (VCNTL = 2.5V, Hi VGA Gain) Gain (dB) 35 LNP = 00 30 25 20 15 10 5 0 0.1 10 Frequency (MHz) LNP = 01 40 1 Frequency (MHz) LNP = 11 LNP = 10 50 Gain (dB) 1 1 10 100 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 100 LNP = 11 LNP = 10 LNP = 01 LNP = 00 0.1 1 10 Frequency (MHz) Frequency (MHz) Figure 11 Figure 12 100 7 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. GAIN vs FREQUENCY (VGA Only) GAIN vs FREQUENCY (LNP Only) 45 25 LNP = 11 20 Hi Gain, VCNTL 2.5V 40 LNP = 10 35 30 15 Gain (dB) Gain (dB) LNP = 01 10 Lo Gain, VCNTL 2.5V 25 20 Hi Gain, VCNTL 0.7V 15 Lo Gain, VCNTL 0.7V 10 5 5 LNP = 00 0 0 -5 -10 -5 0.1 1 10 0.1 100 1 10 Frequency (MHz) Frequency (MHz) Figure 13 Figure 14 GAIN vs FREQUENCY (LNP (G1, G2) = 11, Various VGA Gain Capacitors) OUTPUT-REFERRED NOISE vs VCNTL (VGA Lo Gain, RS = 0) 1000 64 63 LNP 11 62 Noise (nV/Hz) LNP 10 61 Gain (dB) 100 60 59 58 3.9F 0.1F 0.022F 4700pF 57 56 10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 1 LNP 01 LNP 00 10 55 0.1 100 100 Frequency (MHz) VCNTL (V) Figure 15 Figure 16 INPUT-REFERRED NOISE vs VCNTL (LNP and VGA, Lo VGA Gain, RS = 0) OUTPUT-REFERRED NOISE vs VCNTL (VGA Hi Gain, R S = 0) 1000 1000 LNP 11 LNP 10 100 LNP 00 Noise (nV/Hz) Noise (nV/Hz) 100 LNP 01 LNP 00 LNP 01 10 1 LNP 10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 0.1 VCNTL (V) Figure 17 8 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 LNP 11 10 VCNTL (V) Figure 18 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. NOISE FIGURE vs VCNTL (Lo VGA Gain, RS = 0) INPUT-REFERRED NOISE vs VCNTL (Hi VGA Gain, RS = 0) 100 1000 LNP 00 LNP 00 LNP 01 LNP 01 Noise Figure (dB) Noise (nV/Hz) 100 10 LNP 10 LNP 11 1 LNP 10 10 LNP 11 1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 0.1 VCNTL (V) VCNTL (V) Figure 19 Figure 20 NOISE FIGURE vs VCNTL (Hi VGA Gain, RS = 0) OUTPUT-REFERRED NOISE vs VCNTL (VGA Only, RS = 0) 100 1000 LNP 00 Noise (nV/Hz) Noise Figure (dB) LNP 01 LNP 10 10 LNP 11 100 10 1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 1 VCNTL (V) VCNTL (V) Figure 21 Figure 22 INPUT-REFERRED NOISE vs VCNTL (VGA Only) INPUT-REFERRED NOISE vs FREQUENCY (VGA Only) 1000 10 Noise (nV/Hz) 100 Lo Gain 10 1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 Noise (nV/Hz) High Gain VCNTL (V) Figure 23 1 1 10 Frequency (MHz) Figure 24 9 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. INPUT-REFERRED NOISE vs FREQUENCY (LNP Only) DISTORTION vs FREQUENCY (2nd-Harmonic, Lo VGA Gain) -50 10 LNP 00 -52 -54 Distortion (dB) Noise (nV/Hz) LNP 01 1 LNP 10 LNP 11 LNP 11 -56 LNP 10 -58 -60 -62 LNP 00 -64 LNP 01 -66 -68 -70 0.1 1 10 1 10 Frequency (MHz) Frequency (MHz) Figure 25 Figure 26 DISTORTION vs FREQUENCY (3rd-Harmonic, Lo VGA Gain) DISTORTION vs FREQUENCY (2nd-Harmonic, Hi VGA Gain) -50 -40 LNP 11 LNP 10 LNP 01 LNP 00 LNP 11 -54 Distortion (dB) Distortion (dB) -45 -52 -50 -55 LNP 10 -56 -58 -60 LNP 00 -62 LNP 01 -64 -66 -68 -70 -60 1 1 10 Frequency (MHz) Figure 27 Figure 28 DISTORTION vs FREQUENCY (3rd-Harmonic, Hi VGA Gain) 2nd-HARMONIC DISTORTION vs VCNTL (Lo VGA Gain) -40 -30 LNP 11 LNP 10 LNP 01 LNP 00 -50 -35 -40 Distortion (dB) -55 -60 -45 LNP 01 -50 -55 -60 -65 LNP 00 -65 LNP 11 LNP 10 -70 -70 1 10 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 Distortion (dB) -45 10 10 Frequency (MHz) Frequency (MHz) VCNTL (V) Figure 29 Figure 30 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. 2nd-HARMONIC DISTORTION vs VCNTL (Hi VGA Gain) -30 -30 -35 -35 -40 -40 Distortion (dB) -45 -50 -55 -60 -50 -55 -65 -70 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 -70 -45 -60 LNP 00 LNP 01 LNP 10 LNP 11 -65 LNP 00 LNP 10 LNP 01 LNP 11 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 Distortion (dB) 3rd-HARMONIC DISTORTION vs VCNTL (Lo VGA Gain) VCNTL (V) VCNTL (V) Figure 31 Figure 32 3rd-HARMONIC DISTORTION vs VCNTL (Hi VGA Gain) DISTORTION vs VCA Output Voltage -30 -30 LNP 00 LNP 01 LNP 10 LNP 11 -35 Distortion (dB) -40 -45 -50 -55 -45 3rd-Harmonic -50 -55 -60 -60 -65 -65 -70 -70 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 Distortion (dB) -40 -35 2nd-Harmonic 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 VCNTL (V) VCA Output (VPP ) Figure 33 Figure 34 DISTORTION vs LNP Gain (LNP Only) -30 DISTORTION vs VCNTL (VGA Only, SE In/Diff Out, Lo Gain) -20 -35 -30 2nd-Harmonic 2nd-Harmonic -45 Distortion (dB) -50 -55 -60 3rd-Harmonic -65 -70 -40 -50 -60 3rd-Harmonic -70 -75 -80 -80 00 01 10 LNP Gain (G1, G2) Figure 35 11 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 Distortion (dB) -40 VCNTL (V) Figure 36 11 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. DISTORTION vs VCNTL (VGA Only, SE In/Diff Out, Hi Gain) DISTORTION vs OUTPUT LOAD RESISTANCE -30 -30 -35 -35 2nd-Harmonic -40 Distortion (dB) -45 -50 -55 -60 -65 -45 -50 2nd-Harmonic -55 -60 -65 3rd-Harmonic -70 3rd-Harmonic -75 -80 2.5 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 -70 50 150 250 350 450 550 650 750 850 950 1050 RLOAD() VCNTL (V) Figure 37 Figure 38 CROSSTALK vs VCNTL (Lo VGA Gain) CROSSTALK vs VCNTL (Hi VGA Gain) -60 -60 LNP 00 LNP 01 LNP 10 LNP 11 -62 -64 Crosstalk (dB) -66 -68 -70 -72 -74 -66 -68 -70 -72 -74 -78 -80 -80 0.7 0.8 -76 -78 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 -76 0.7 0.8 VCNTL (V) VCNTL (V) Figure 39 -50 Figure 40 CROSSTALK vs VCNTL (VOUT = 2VPP, Hi-Gain) TOTAL POWER vs TEMPERATURE 314 -54 313 312 10MHz -62 -66 5MHz -70 -74 2MHz -78 310 309 308 307 306 -82 305 -86 1MHz 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 -90 VCNTL (V) Figure 41 12 311 Power (mW) Crosstalk (dB) -58 304 303 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 Crosstalk (dB) -64 LNP 00 LNP 01 LNP 10 LNP 11 -62 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 Distortion (dB) -40 Temperature (_ C) Figure 42 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. VGA POWER vs TEMPERATURE LNP POWER vs TEMPERATURE 96.0 Power Dissipation (mW) 238 237 236 235 233 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 234 95.5 95.0 94.5 94.0 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 VGA Power Dissipation (mW) 239 Temperature (_ C) Temperature (_ C) Figure 43 Figure 44 GAIN vs VCNTL vs TEMPERATURE DISTORTION vs TEMPERATURE -60 50 45 -59 2nd-Harmonic 40 -57 -56 -55 30 25 -40_ C 20 +85_ C 15 -54 10 3rd-Harmonic -53 5 0 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Temperature (_ C) VCNTL (V) -30 -31 -32 -33 -34 -35 -36 -37 -38 -39 -40 -41 -42 -43 -44 -45 -46 0.25 Figure 46 VOUT vs VCLAMP (100mVPP, S/E Input) OVERLOAD DISTORTION 2nd-HARMONIC VOUT (PP) 2nd-Harmonic (dB) Figure 45 0.50 0.75 VIN (V) Figure 47 1.00 5.2 4.8 4.4 4.0 3.6 3.2 2.8 2.4 2.0 1.6 1.2 0.8 0.4 0 H/L = 0 H/L = 1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 -52 +25_ C 35 Gain (dB) Distortion (dB) -58 VCLAMP (V) Figure 48 13 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25C, VDD = 5V, load resistance = 500 on each output to ground; the input to the preamp (LNP) is single-ended; fIN = 5MHz, LNP Gain (G1, G2) = 10, H/L = 0, VCNTL = 2.5V; VCA output is 1VPP differential; CA, CB = 3.9F, unless otherwise noted. OUTPUT IMPEDANCE vs FREQUENCY POWER UP/DOWN RESPONSE PD Pin 100 H 10 1VPP VGA Output (V) ROUT () L 1 0.1 1 10 100 0 Frequency (MHz) 5 10 15 20 25 30 35 40 45 50 55 60 Time (s) Figure 49 Figure 50 GROUP DELAY vs FREQUENCY GAIN CONTROL TRANSIENT RESPONSE 2V 30 Group Delay (ns) 0V 1VPP VGA Output (V) VCNTL (V) 35 25 20 15 10 5 0 0 0.3 0.6 0.9 1.2 1.5 1.8 Time (s) Figure 51 14 2.1 2.4 2.7 3.0 1 10 Frequency (MHz) Figure 52 100 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 THEORY OF OPERATION The VCA2615 is a dual-channel system consisting of two primary blocks: a low noise preamplifier (LNP) and a variable gain amplifier (VGA), which is driven from the LNP. The LNP is very flexible; both the gain and input impedance can be programmed digitally without using external components. The LNP is coupled to the VGA through a multiplexer to facilitate interfacing with an external signal processor. The VGA is a true variable-gain amplifier, achieving lower noise output at lower gains. The output amplifier has two gains, allowing for further optimization with different analog-to-digital converters. Figure 53 shows a simplified block diagram of a single channel of the dual-channel system. Both the LNP and the VGA can be powered down together or separately in order to conserve system power when necessary. LNP VGA Figure 53. Simplified Block Diagram of VCA2615 LNP--OVERVIEW The LNP has differential input and output capability. It also has exceptionally low noise voltage and input current noise. At the highest gain setting (of 22dB), the LNP achieves 0.7nV/Hz voltage noise and typically 1pA/Hz current noise. The LNP can process fully differential or single-ended signals in each channel. Differential signal processing reduces second harmonic distortion and offers improved rejection of common-mode and power-supply noise. The LNP gain can be electronically programmed to have one of four values that can be selected by a two-bit word (see Table 2). The gain of the LNP when driving the VGA is approximately 1dB higher because of the loss in the buffer. The LNP also has four programmable feedback resistors that can be selected by a four-bit word to create 16 different values in order to facilitate the easy use of active feedback. With this combination of both programmable gain and feedback resistors, as many as 61 different values of input impedance can be created to provide a wide variety of input-matching resistors (see Table 5). By using active feedback with this wide selection of feedback resistors, the user is able to provide a low-noise means of terminating input signal while incurring only a 3dB loss in signal-to-noise ratio (SNR), instead of a 6dB loss in SNR which is usually associated with the conventional type of signal termination. More information is given in the section of this document that provides a detailed description of the LNP. The LNP output drives a buffer that in turn drives the feedback network and supplies the LNP to a multiplexer. The multiplexer can be configured to supply the signal off-chip for further processing, or can be set to drive the internal VGA directly from the LNP. An external coupling capacitor is not required to couple the LNP to the VGA. VGA--OVERVIEW The VGA that is used with the VCA2615 is a true variable-gain amplifier; as the gain is reduced, the noise contribution from the VGA itself is also reduced. A block diagram of the VGA is shown in Figure 53. This design is in contrast with another popular device architecture (used by the VCA2616), where an effective VCA characteristic is obtained by a voltage variable-attenuator succeeded by a fixed-gain amplifier. At the highest gain, systems with either architecture are dominated by the noise produced by the LNP. At low gains, however, the noise output is dominated by the contribution from the VGA. Therefore, the overall system with lower VGA gain will produce less noise. The following example will illustrate this point. Figure 53 shows a block diagram of an LNP driving a variable-gain amplifier; Figure 54 shows a block diagram of an LNP driving a variable attenuation attenuator followed by a fixed gain amplifier. For purposes of this example, let us assume the performance characteristics shown in Table 1; these values are the typical performance data of the VCA2615 and the VCA2616. LNP ATTENUATOR Amplifier Figure 54. Block Diagram of Older VCA Models 15 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 Table 1. Gain and Noise Performance of Various VCA Blocks BLOCK GAIN (Loss) dB NOISE nV/Hz LNP1 (VCA2615) 20 0.82 LNP2 (VCA2616) 20 1.1 Attenuator (VCA2616) 0 1.8 Attenuator (VCA2616) -40 1.8 VCA1 (VCA2615) 40 3.8 VCA1 (VCA2615) 0 90 VCA2 (VCA2616) 40 2.0 Total Noise + (LNP Noise)2 ) (VCA NoiseLNP Gain) 2 + (0.82)2 ) (3.810) 2 + 0.90nV Hz (1) When the block diagram shown in Figure 54 has the combined gain of 60dB, the noise referred to the input (RTI) is given by the expression: Total Noise (RTI) + (LNP Noise)2 ) (ATTEN NoiseLNP Gain)2 ) (VCA NoiseLNP Gain)2 + (1.1) 2 ) (1.810) 2 ) (2.010) 2 + 1.13nV Hz (2) Repeating the above measurements for both VCA configurations when the overall gain is 20dB yields the following results: (0.82)2 ) (9010)2 + 9.03nV Hz LOW NOISE PREAMPLIFIER (LNP)--DETAIL The LNP is designed to achieve exceptionally low noise performance when employed with or without active feedback. The proprietary LNP architecture can be electronically programmed, eliminating the need for off-board components to alter the gain. A simplified schematic of this amplifier is shown in Figure 55. FET pairs Q1-Q2, Q3-Q4, Q5-Q6 and Q7-Q8 each represent a different LNP gain. The four switches are 22dB, 18dB, 12dB and 3dB. One of the unique gain settings is selected when one of the four switches Q9 through Q12 are selected. Table 2 shows the relationship between the gain selection bits, G1 and G2, and the corresponding gain. Table 2. Gain Selection of LNP (3) LNP GAIN (dB) G1 G2 0 0 3 0 1 12 1 0 18 1 1 22 VDD Q13 Digital Gain Select Q9 Q10 Q11 Q14 Q12 -IN +IN Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 -OUT +OUT Figure 55. Programmable LNP 16 (4) The VGA has a continuously-variable gain range of 52dB with the ability to select either of two options. The gain of the VGA can either be varied from -12dB to 40dB, or from -18dB to 34dB. The VGA output can be programmed to clip precisely at a predetermined voltage that is selected by the user. When the user applies a voltage to pin 18 (VCLMP), the output will have a peak-to-peak voltage that is given by the graph shown in Figure 48. For the VCA with a variable gain amplifier (Figure 53): Total Noise (RTI) + (1.1)2 ) (1.810) 2 ) (2.00.10)2 + 14nV Hz When the block diagram shown in Figure 53 has a combined gain of 60dB, the noise referred to the input (RTI) is given by the expression: Total Noise (RTI) + For the VCA with a variable attenuation attenuator (Figure 54): " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 The ability to change the gain electronically offers additional flexibility for optimizing the gain in order to achieve either maximum signal-handling capability or maximum sensitivity. Table 3 lists the input and output signal-handling capability of the LNP. LNP Gain 11 00 (10V/div) Table 4 shows the voltage noise of the LNP for different gain settings. Table 3. Signal Handling Capability of LNP 11 MAX INPUT (VPP Single-Ended) 0.23 MAX OUTPUT (VPP Differential) 3.5 18 10 0.39 3.5 12 01 0.78 3.5 3 00 2.3 3.0 GAIN (dB) G1, G2 22 VOLTAGE NOISE (nV/Hz) at 5MHz 22 0.8 18 1.1 12 1.9 3 4.9 Time (200ns/div) Figure 57. LNP Gain Change Response The LNP also feeds a MUX, which accepts the LNP signal or can receive an external signal. When applying an external signal to the MUX (VCAIN), the signal should be biased to a common-mode voltage in the range of 1.85V to 3.15V. This biasing could be accomplished by using the 2.5V level of the VCM pin (19) of the VCA2615. Table 4. LNP Gain vs Voltage Noise LNP GAIN (dB) LNP Output (500mV/div) The current noise for the LNP is 1pA/Hz for all gain settings. The input capacitance of the LNP is 45pF. The LNP output drives a buffer and a multiplexer (MUX) along with a feedback network that can be used to program the input impedance. Figure 56 shows a block diagram of how these circuits are connected together. The output of the LNP feeds a buffer to avoid the loading effect of the feedback resistors and to achieve a more robust capability for driving external circuits. To MUX (VGAIN ) IN VCM Figure 58. Recommended Circuit for Coupling an External Signal into the MUX INPUT IMPEDANCE Feedback Resistors Figure 59 shows a simplified schematic of the resistor feedback network along with Table 5 that relates the FB1, FB2, FB3 and FB4 code to the selected value. When the selection bits leave the feedback network in the open position, the input resistance of the LNP will become 100k. LNP OUT Buffer IN LNP MUX VGA OUT 1500 (FB1) 1000 (FB2) 500 (FB3) 250 (FB4) VGA IN Figure 56. Block Diagram of LNP/VGA Interface See Figure 57, which shows the response time of the LNP gain changing from minimum to maximum. IN LNP Buffer OUT Figure 59. Feedback Resistor Network 17 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 Table 5. Feedback Resistor Settings FEEDBACK RESISTOR (W) FB4 FB3 FB2 FB1 130 0 0 0 0 143 0 0 0 1 150 0 0 1 0 167 0 0 1 1 176 0 1 0 0 200 0 1 0 1 214 0 1 1 0 250 0 1 1 1 273 1 0 0 0 333 1 0 0 1 375 1 0 1 0 500 1 0 1 1 600 1 1 0 0 1000 1 1 0 1 1500 1 1 1 0 Open 1 1 1 1 wasted in the termination resistor itself. Another example may clarify this point. First, consider that the input source, at the far end of the signal cable, has a cable-matching source resistance of RS. Using a conventional shunt termination at the LNP input, a second terminating resistor RS is connected to ground. Therefore, the signal loss is 6dB because of the voltage divider action of the series and shunt RS resistors. The effective source resistance has been reduced by the same factor of two, but the noise contribution has been reduced only by the 2, which is only a 3dB reduction. Therefore, the net theoretical SNR degradation is 3dB, assuming a noise-free amplifier input. In practice, the amplifier noise contribution will degrade both the un-terminated and the terminated noise figures. Figure 60 shows an amplifier using active feedback. RF RS As explained previously, the LNP gain can have four different values while the feedback resistor can be programmed to have 16 different values. This variable gain means that the input impedance can take on 61 different values given by the formula shown below: R IN + A RIN RIN = RF (1 ) ALNP 2 Active Feedback RF = RS 1+A RS ) (5) Where RF is the value of the feedback resistor and ALNP is the differential gain of the LNP in volts/volt. The variable gain enables the user to most precisely match the LNP input impedance to the various probe and cable impedances to achieve optimum performance under a variety of conditions. No additional components are required in order to determine the input impedance. The resistor values shown in Table 5 represent typical values. Due to process variation, the actual values of the resistance can differ by as much as 20%. ACTIVE FEEDBACK TERMINATION One of the key features of an LNP architecture is the ability to employ active-feedback termination in order to achieve superior noise performance. Active-feedback termination achieves a lower noise figure than conventional shunt termination essentially because no signal current is 18 LNPIN A RS Conventional Cable Termination Figure 60. Configurations for Active Feedback and Conventional Cable Termination This diagram appears very similar to a traditional inverting amplifier. However, A in this case is not a very large open-loop op-amp gain; rather, it is the relatively low and controlled gain of the LNP itself. Thus, the impedance at the inverting amplifier terminal will be reduced by a finite amount, as given in the familiar relationship of: R IN + RF (1 ) A) (6) where RF is the programmable feedback resistor, A is the user-selected gain of the LNP, and RIN is the resulting amplifier input impedance with active feedback. " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 In this case, unlike the conventional termination shown in Figure 60, both the signal voltage and the RS noise are attenuated by the same factor of two (or 6dB) before being re-amplified by the A gain setting. This configuration avoids the extra 3dB degradation because of the square-root effect described above, which is the key advantage of the active termination technique. As noted, the previous explanation ignored the input noise contribution of the LNP itself. Also, the noise contribution of the feedback resistor must be included for a completely correct analysis. The curves shown in Figure 61 and Figure 62 allow the VCA2615 user to compare the achievable noise figure for active and conventional termination methods. VCA NOISE = 3.8nVHz, LNP GAIN = 20dB 9 LNP Noise nV/Hz 6.0E-10 8.0E-10 1.0E-09 1.2E-09 1.4E-09 1.6E-09 1.8E-09 2.0E-09 8 Noise Figure (dB) 7 6 5 4 3 2 1 0 0 100 200 300 400 500 600 700 800 900 1000 Source Impedance () Figure 61. Noise Figure for Active Termination VCA NOISE = 3.8nVHz, LNP GAIN = 20dB 14 LNP Noise nV/Hz 6.0E-10 8.0E-10 1.0E-09 1.2E-09 1.4E-09 1.6E-09 1.8E-09 2.0E-09 Noise Figure (dB) 12 10 8 6 4 2 0 0 100 200 300 400 500 600 700 800 900 1000 Source Impedance () Figure 62. Noise Figure for Conventional Termination VOLTAGE-CONTROLLED AMPLIFIER (VCA)-- DETAIL Figure 63 shows a simplified schematic of the VCA. The VCA2615 is a true voltage-controlled amplifier, with the gain expressed in dB directly proportional to a control signal. This architecture compares to the older VCA products where a voltage-controlled attenuator was followed by a fixed-gain amplifier. With a variable-gain amplifier, the output noise diminishes as the gain reduces. A variable-gain amplifier, where the output amplifier gain is fixed, will not show diminished noise in this manner. Refer to Table 6, which shows a comparison between the noise performance at different gains for the VCA2615 and the older VCA2616. Table 6. Noise vs Gain (RG = 0) PRODUCT GAIN (dB) NOISE RTI (nV/Hz) VCA2615 60 0.7 VCA2615 20 9.0 VCA2616 60 1.1 VCA2616 20 14.0 The VCA accepts a differential input at the +IN and -IN terminals. Amplifier A1, along with transistors Q2 and Q3, forms a voltage follower that buffers the +IN signal to be able to drive the voltage-controlled resistor. Amplifier A3, along with transistors Q27 and Q28, plays the same role as A1. The differential signal applied to the voltage-controlled resistor network is converted to a current that flows through transistors Q1 through Q4. Through the mirror action of transistors Q1/Q5 and Q4/Q6, a copy of this same current flows through Q5 and Q6. Assuming that the signal current is less than the programmed clipping current (that is, the current flowing through transistors Q7 and Q8), the signal current will then go through the diode bridge (D1 through D4) and be sent through either R2 or R1, depending upon the state of Q9. This signal current multiplied by the feedback resistor associated with amplifier A2, determines the signal voltage that is designated -OUT. Operation of the circuitry associated with A3 and A4 is identical to the operation of the previously described function to create the signal +OUT. A1 and its circuitry form a voltage-to-current converter, while A2 and its circuitry form a current-to-voltage converter. This architecture was adapted because it has excellent signal-handling capability. A1 has been designed to handle a large voltage signal without overloading, and the various mirroring devices have also been sized to handle large currents. Good overload capability is achieved as both the input and output amplifier are not required to amplify voltage signals. 19 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 impedance connection to join the two sections of the resistor network. Capacitor C could be replaced by a short-circuit. By providing a DC connection, the output offset will be a function of the gain setting. Typically, the offset at this point is 10mV; thus, if the gain varies from 1 to 100, the output offset would vary from 10mV to 100mV. Voltage amplification occurs when the input voltage is converted to a current; this current in turn is converted back to a voltage as amplifier A2 acts as a transimpedance amplifier. The overall gain of the output amplifier A2 can be altered by 6dB by the action of the H/L signal. This enables more optimum performance when the VCA interfaces with either a 10-bit or 12-bit analog-to-digital converter (ADC). An external capacitor (C) is required to provide a low Clipping Program Circuitry VDD H/L R1 Q1 Q5 Q7 Q9 R2 +IN Q2 D1 D2 D3 D4 A1 Q3 A2 VCM Q4 Q6 External Capacitor Q8 VCNTL Q10 Q12 Q14 Q16 Q18 Q20 Q22 Q24 CEXT 2 VCA Program Circuitry C CEXT 1 Q11 Q13 Q15 Q17 Q19 Q21 Q23 Q25 Voltage-Controlled Resistor Network Q26 Q30 Control Signal Q32 VCM Q27 D5 D6 D7 D8 A4 A3 R3 Q28 -IN R4 Q29 Q31 Q33 Q34 VDD Clipping Program Circuitry VCLMP Figure 63. Block Diagram of VCA 20 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 VARIABLE GAIN CHARACTERISTICS Transistors Q10, Q12, Q14, Q16, Q18, Q20, Q22, and Q24 form a variable resistor network that is programmed in an exponential manner to control the gain. Transistors Q11, Q13, Q15, Q17, Q19, Q21, Q23, and Q25 perform the same function. These two groups of FET variable resistors are configured in this manner to balance the capacitive loading on the total variable-resistor network. This balanced configuration is used to keep the second harmonic component of the distortion low. The common source connection associated with each group of FET variable resistors is brought out to an external pin so that an external capacitor can be used to make an AC connection. This connection is necessary to achieve an adequate low-frequency bandwidth because the coupling capacitor would be too large to include within the monolithic chip. The value of this variable resistor ranges in value from 15 to 5000 to achieve a gain range of about 44dB. The low-frequency bandwidth is then given by the formula: Low Frequency BW + 12pRC Channel 1 VCNTL (2V/div) Channel 2 Output (20mV/div) Time (400ns/div) Figure 64. Response to Step Change of VCNTL (7) where: R is the value of the attenuator. Channel 1 VCNTL (2V/div) C is the value of the external coupling capacitor. For example, if a low-frequency bandwidth of 500kHz was desired and the value of R was 15, then the value of the coupling capacitor would be approximately 22nF. One of the benefits of this method of gain control is that the output offset is independent of the variable gain of the output amplifier. The DC gain of the output amplifier is extremely low; any change in the input voltage is blocked by the coupling capacitor, and no signal current flows through the variable resistor. This method also means that any offset voltage existing in the input is stored across this coupling capacitor; when the resistor value is changed, the DC output will not change. Therefore, changes in the control voltage do not appear in the output signal. Figure 64 shows the output waveform resulting from a step change in the control voltage, and Figure 65 shows the output voltage resulting when the control voltage is a full-scale ramp. Channel 2 Output (20mV/div) Time (400ns/div) Figure 65. Response to Ramp Change of VCNTL The exponential gain control characteristic is achieved through a piecewise approximation to a perfectly smooth exponential curve. Eight FETs, operated as variable resistors whose value is progressively 1/2 of the value of the adjacent parallel FET, are turned on progressively, or their value is lowered to create the exponential gain characteristic. This characteristic can be shown in the following way. An exponential such as y = ex increases in the y dimension by a constant ratio as the x dimension increases by a constant linear amount. In other words, for a constant (x1 - x2), the ratio ex1/ex2 remains the same. When FETs used as variable resistors are placed in parallel, the attenuation characteristic that is created behaves according to this same exponential characteristic at discrete points as a function of the control voltage. It does not perfectly obey an ideal exponential characteristic at other points; however, an 8-section approximation yields a 1dB error to an ideal curve. 21 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 PROGRAMMABLE CLIPPING The clipping level of the VCA can be programmed to a desired output. The programming feature is useful when matching the clipped level from the output of the VCA to the full-scale range of a subsequent VCA, in order to prevent the VCA from generating false spectral signals; see the circuit diagram shown in Figure 66. The signal node at the drain junction of Q5 and Q6 is sent to the diode bridge formed by diode-connected transistors, D1 through D4. The diode bridge output is determined by the current that flows through transistors Q7 and Q8. The maximum current that can then flow into the summing node of A2 is this same current; consequently, the maximum voltage output of A2 is this same current multiplied by the feedback resistor associated with A2. The maximum output voltage of A2, which would be the clipped output, can then be controlled by adjusting the current that flows through Q7 and Q8; see the circuit diagram shown in Figure 63. The circuitry of A1, R2, and Q2 converts the clamp voltage (VCLMP) to a current that controls equal and opposite currents flowing through transistors Q5 and Q6. When H/L = 0, the previously described circuitry is designed so that the value of the VCLMP signal is equal to the peak differential signal developed between +VOUT and -VOUT. When H/L = 1, the differential output will be equal to the clamp voltage. This method of controlled clipping also achieves fast and clean settling waveforms at the output of the VCA, as shown in Figure 67 through Figure 70. The sequence of waveforms demonstrate the clipping performance during various stages of overload. The VCLMP pin represents a high impedance input (> 100k). In a typical application, the VCA2615 will drive an anti-aliasing filter, which in turn will drive an ADC. Many modern ADCs, such as the ADS5270, are well-behaved with as much as 2x overload. This means that the clipping level of the VCA should be set to overcome the loss in the filter such that the clipped input to the ADC is just slightly over the full-scale input. By setting the clipping level in this manner, the lowest harmonic distortion level will be achieved without interfering with the overload capability of the ADC. VDD R1 Q9 Q1 Q7 Q5 R2 VCLMP A1 From Buffered Input Q2 Clip Adjust Input D1 D2 D3 D4 H/L A2 VCM Output Amp R2 Q6 Q8 Figure 66. Clipping Level Adjust Circuitry 22 " #$%& www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 LNP Input (50mV/div) LNP Input (100mV/div) Differential Output (500mV/div) Differential Output (500mV/div) VCNTL = 0.7V Time (200ns/div) Figure 67. Before Overload (100mVPP Input) VCNTL = 0.7V Figure 69. Overload (240mVPP Input) LNP Input (50mV/div) LNP Input (500mV/div) Differential Output (500mV/div) Differential Output (1V/div) VCNTL = 0.7V Time (200ns/div) Figure 68. Approaching Overload (120mVPP Input) Time (200ns/div) VCNTL = 0.7V Time (200ns/div) Figure 70. Extreme Overload (2VPP Input) POWER-DOWN MODES When VDD (5V) is applied to the VCA2615, the total power dissipation is typically 308mW. When the power is initially applied to the VCA2615 with both PDV and PDL pins at a logic low, the typical power dissipation will be 5mW. After the VCA2615 has been enabled, if the PDL line is low with the PDV line high, the typical power dissipation will be approximately 100mW. After the VCA2615 has been enabled, if the PDV line is low with the PDL line high, the typical power dissipation will be approximately 200mW. 23 www.ti.com SBOS316D - JULY 2005 - REVISED OCTOBER 2008 Revision History DATE 10/08 REV D PAGE SECTION DESCRIPTION 1 Features Deleted SMALL QFN-48 PACKAGE (7x7mm) 1 Description Text added to last paragraph. 2 Package/Ordering Added TQFP-48 package information. 4 Electrical Characteristics Thermal Characteristics section; added text. 1 Features Changed 20dB/V to 22dB/V under LOW-NOISE VARIABLE-GAIN AMPLIFIER 3 Electrical Characteristics Added CA, CB = 3.9F to the overall conditions. Accuracy section; moved Gain Slope line under accurary, added "VCNTL = 0.4V to 2.0V" to conditions, and changed typical value from 20dBv to 22dB/V. 8/05 C 4 Electrical Characteristics 5 Pin Configuration Pin 19 description; changed 0.01F to 0.1F. 22 Programmable Clipping Reworded paragraph three to clarify description of setting VCA clipping level. Thermal Characteristics section; removed "Specified" and added "Operating" to conditions. NOTE: Page numbers for previous revisions may differ from page numbers in the current version. 24 PACKAGE OPTION ADDENDUM www.ti.com 8-Dec-2009 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Eco Plan (2) Qty VCA2615PFBR ACTIVE TQFP PFB 48 1000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR VCA2615PFBT ACTIVE TQFP PFB 48 250 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR VCA2615RGZR ACTIVE VQFN RGZ 48 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR VCA2615RGZRG4 ACTIVE VQFN RGZ 48 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR VCA2615RGZT ACTIVE VQFN RGZ 48 250 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR VCA2615RGZTG4 ACTIVE VQFN RGZ 48 250 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR Lead/Ball Finish MSL Peak Temp (3) (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 14-Jul-2012 TAPE AND REEL INFORMATION *All dimensions are nominal Device VCA2615PFBR Package Package Pins Type Drawing TQFP PFB 48 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant 1000 330.0 16.4 9.6 9.6 1.5 12.0 16.0 Q2 VCA2615PFBT TQFP PFB 48 250 330.0 16.4 9.6 9.6 1.5 12.0 16.0 Q2 VCA2615RGZR VQFN RGZ 48 2500 330.0 16.4 7.3 7.3 1.5 12.0 16.0 Q2 VCA2615RGZT VQFN RGZ 48 250 180.0 16.4 7.3 7.3 1.5 12.0 16.0 Q2 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 14-Jul-2012 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) VCA2615PFBR TQFP PFB 48 1000 367.0 367.0 38.0 VCA2615PFBT TQFP PFB 48 250 367.0 367.0 38.0 VCA2615RGZR VQFN RGZ 48 2500 367.0 367.0 38.0 VCA2615RGZT VQFN RGZ 48 250 210.0 185.0 35.0 Pack Materials-Page 2 MECHANICAL DATA MTQF019A - JANUARY 1995 - REVISED JANUARY 1998 PFB (S-PQFP-G48) PLASTIC QUAD FLATPACK 0,27 0,17 0,50 36 0,08 M 25 37 24 48 13 0,13 NOM 1 12 5,50 TYP 7,20 SQ 6,80 9,20 SQ 8,80 Gage Plane 0,25 0,05 MIN 0- 7 1,05 0,95 Seating Plane 0,75 0,45 0,08 1,20 MAX 4073176 / B 10/96 NOTES: A. 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