Agilent ABA-52563 3.5 GHz Broadband Silicon RFIC Amplifier Application Note 1349 GND 2 Input Introduction Agilent Technologies' ABA-52563 is a low current silicon gain block RFIC amplifier housed in a 6 lead SC-70 (SOT-363) surface mount plastic package. Providing a nominal gain of 21.3 dB and P1dB of 9.7 dBm at 2 GHz, this device is ideal for small signal gain stage or IF amplification. Distinguished features of the ABA-52563 which are high gain, good input and output VSWR and Output & Vcc 2Hx GND 1 GND 3 Vcc broad bandwidth made this device useful in various applications such as Cellular, Cordless, Special Mobile Radio, PCS, ISM, Wireless LAN, DBS, TVRO and TV Tuner Applications. In addition to the ABA-52563, Agilent Technologies also offers a series of ABA devices with a range of P1dB. The table below is a quick reference on the performance of the series measured at 2 GHz on the board. Symbol Unit ABA-51563 ABA-52563 ABA-53563 P1dB dBm 1.8 9.7 12.5 OIP3 dBm 11.4 20.1 22.6 Icc mA 18.4 34.9 46.3 Gp dB 21.3 21.3 21.3 NF dB 3.6 3.6 3.6 VSWR in <1.2 <1.2 <1.2 VSWR out <1.4 <1.4 <1.4 Application Guidelines The ABA-52563 is designed with a two stage cascade consisting in general of a single input transistor driving a Darlington connected output pair. Resistive feedback is used to set the RF performance. The collector of the first stage directly drives the base of the output stage without any interstage blocking capacitor that would limit the low frequency response. The second stages is fed back using both series and shunt resistors, sets the match, gain and flatness of the RFIC. The Agilent's HP25 silicon bipolar process with a cut off frequency, fT of 25 GHz results in a device with low current draw and useful operation up to 3.5 GHz. The ABA-52563 is very easy to use. For most applications, all that is required to operate the device is to apply a voltage to Pin 4 (Vcc) and Pin 6 (Output and Vcc). All bias regulation circuitry is integrated into the RFIC. RF Input and Output The RF Input and Output ports of the ABA-52563 are closely matched to 50. DC Bias The ABA-52563 is a voltagebiased device that operates at 5V with nominal current of 35 mA. Figure 1 shows a typical implementation of ABA-52563. Cblock RF Output 2Hx RFC RF Input Vcc Cblock Figure 1. Typical Application Circuit. 2 Cbypass The supply voltage for the ABA-52563 must be applied to two terminals, the Vcc and the RF Output pins. The Vcc connection to the amplifier is RF bypassed by placing a capacitor to ground near the Vcc pin of the amplifier package. The power supply connection to the RF Output pin is achieved by means of a RF choke (inductor). The reactance of the RF choke must be relatively higher to 50 in order to prevent loading of the RF Output. Blocking capacitors are normally placed in series with the RF input and RF Output to isolate the DC voltages on these pins from circuit adjacent to the amplifier. The values of the blocking capacitors are selected to provide a reactance at the lowest frequency of operation that is relatively smaller to 50. PCB Layout The ABA-52563 is packaged in the miniature SOT-363 (SC-70) surface mount package. A PCB pad layout for the SOT-363 package is shown in Figure 2. This layout provides ample allowance for package placement by automated assembly equipment without adding pad parasitic that could impair the high frequency performance of the ABA-52563. The layout is shown with a nominal SOT-363 package footprint superimposed on the PCB pads for reference. PCB Materials Typical choices for PCB material for low cost wireless applications are FR-4 or G-10 with a thickness of 0.025 or 0.032 inches. A thickness of 0.062 inches is the maximum that is recommended for use with this particular device. The use of a thicker board material increases the inductance of the plated through vias used for RF grounding and may deteriorate circuit performance. Adequate grounding is needed not only to obtain maximum amplifier performance but also to reduce any possibility of instability. 0.026 (0.65) 0.07 (1.75) 0.035 (0.875) 0.016 (0.4) Figure 2. PCB Pad Layout. Dimensions are in inches (millimeters). 3 Application Example An example layout for an amplifier using the ABA-52563 is shown in Figure 3. This example uses a microstrip line design (solid ground plane on the backside of the circuit board). The circuit board material is 0.032-inch thick FR-4. Plated through holes (vias) are used to bring the ground to the topside of the circuit where needed. Multiple vias are used to reduce the inductance of the path to ground. ABA-5XX63 DEMO BOARD INPUT OUTPUT Vcc Figure 3. RF Layout. Figure 4 shows an assembled amplifier. The +5 volt supply is fed directly into the Vcc pin of the ABA-52563 and into the RF Output pin through the RF choke (RFC). DC blocking capacitors are required at the input and output of the IC. The values of blocking capacitors are determined by the lowest frequency of operation for a particular application. The capacitor's reactance is chosen to be 10% or less of the amplifier's input or output impedance at the lowest operating frequency. For example, an The Vcc connection to the amplifier must be RF bypassed by placing a capacitor to ground at the bias pad of the board. Like the DC blocking capacitors, the value of the Vcc bypass capacitor is determined by the lower operating frequency for the amplifier. The reactance of the RF choke should be large compared to 50, a typical value for 1.9 GHz amplifier would be 22 nH. For this demonstration board, capacitor C3 provides RF bypassing for both the Vcc pin and the power supply end of the RFC. Capacitor C4 is optional and may be used to add additional bypassing for the Vcc line. A well bypassed Vcc line is especially necessary in cascades of amplifier stages to prevent oscillation that may occur as a result of RF feedback through the power supply lines. The value chosen for the RF choke was 620 nH. All of the blocking and bypass capacitors are 1000 pF. These values provide excellent amplifier performance from 50 MHz through 2 GHz. Larger values for the choke and capacitors can be used to extend the lower end of the bandwidth. Since the gain of the ABA-52563 extends down to DC, the frequency response of the amplifier is limited only by the values of the capacitors and choke. Table 1 consists of the components used to assemble the board. The measurements can be seen at Figure 5 to Figure 7. A convenient method for making RF connection to the demonstration board is to use a PCB mounting type of SMA connector (Johnson 142-0701-881, or equivalent). These connectors can be slipped over the edge of the PCB and the center conductors soldered to the input and output lines. The ground pins of the connectors are soldered to the ground plane on the backside of the board. The extra ground pins for the top of the board are not needed and can be clipped off. RF design software such as Agilent Technologies' AppCad is very handy to determine the values of the blocking capacitors and RF choke for any operating frequency. This software is available at http:// www.agilent.com/view/AppCad Table 1. List of Components. 50 MHz to 2 GHz Component Value Part number C1, C2, C3 RFC C4 (optional) SMA Connectors 1000 pF 620 nH 1 F Murata GRM40X7R102K50 Coilcraft 1008CS-621XXKBC1 Johnson 142-0701-881 ABA-5XX63 DEMO BOARD INPUT OUTPUT 2Hx amplifier to be used in an application covering the 1.9 GHz band would require an input blocking capacitor of at least 19 pF, which is 5 of reactance at 1.9 GHz. C1 C2 RFC C3 C4 Vcc Figure 4. Assembled Amplifier. 4 30 20 S (dB), NF (dB) 10 0 NF S21 S11 S12 S22 -10 -20 -30 -40 -50 1 2 3 4 FREQUENCY (GHz) Figure 5. S parameters and Noise Figure vs. Frequency. 24 -55C 25C 125C 22 GAIN (dB) 20 18 16 14 12 10 1000 2000 3000 4000 FREQUENCY (GHz) Figure 6. Gain vs. Frequency and Temperature. 30 10 2 GHz 0 P1dB INPUT -10 OUTPUT 2Hx Pout (dBm) 20 C1 -20 RFC -30 -40 -30 -20 Pin (dBm) Figure 7. P1dB. 5 C2 -10 0 C3 Figure 8. Magnified Assembled Board. Notes on RF Grounding As a direct result of the circuit topology discussed in the earlier paragraph, the performance of ABA-52563 is extremely sensitive to ground path ("emitter") inductance. The two-stage design potentially creates a feedback loop being formed through the ground returns of the stages. If the path to ground provided by the external circuit is "long" (high in impedance) compared to the path back through the ground return of the other stage, then instability can occur. right at the device is essential. The designs should be done on the thinnest practical substrate. The parasitic inductance of a pair of via passing through 0.032 inches thick PC board is approximately 0.1 nH, while that of a pair via holes passing through 0.062 inches is closer to 0.5 nH. It is recommended that the PCB trace for the ground pins NOT be connected together underneath the body of the package. PCB pads hidden under the package cannot be adequately inspected for SMT solder quality. This phenomena can show up as a "peaking" in the gain versus frequency response (perhaps creating a negative gain slope amplifier), an increase in input VSWR or even as return gain (a reflection coefficient greater than unit) at the input of the RFIC. These stability effects are entirely predictable. A circuit simulation using the datasheet S-parameters and including a description of the ground path (via model or equivalent "emitter" inductance) will give an accurate picture of the performance that can be expected. Device characterizations are made with the ground leads of the ABA-52563 directly contacting a solid copper block (system ground) at a distance of 2 to 4 mils from the body of the Evidently, an excellent grounding is critical when using ABA-52563. The use of plated through holes or equivalent minimal path ground returns 6 package. Thus the information in the datasheet is a true description of the performance capability of the RFIC, and contains minimal contributions from the test fixture. Phase Reference Planes The positions of the reference planes used to measure S-parameters for this device are shown in Figure 9. As seen in the illustration, the reference planes are located at the point where the package leads contact the test circuit. Reference Planes Test Circuit Figure 9. Phase Reference Plane. 7 www.agilent.com/semiconductors For product information and a complete list of distributors, please go to our web site. For technical assistance call: Americas/Canada: +1 (800) 235-0312 or (408) 654-8675 Europe: +49 (0) 6441 92460 China: 10800 650 0017 Hong Kong: (+65) 6271 2451 India, Australia, New Zealand: (+65) 6271 2394 Japan: (+81 3) 3335-8152(Domestic/International), or 0120-61-1280(Domestic Only) Korea: (+65) 6271 2194 Malaysia, Singapore: (+65) 6271 2054 Taiwan: (+65) 6271 2654 Data subject to change. Copyright (c) 2003 Agilent Technologies, Inc. Obsoletes 5988-8966EN March 25, 2003 5988-9198EN