May 12, 2004
Demo Circuit DC550A Quick Start Guide.
Introduction
Demo circuit DC550A demonstrates operation of the LT5514 IC, a DC-850MHz bandwidth ‘open
loop’ transconductance amplifier with high impedance ‘open collector’ outputs. LT5514 consists of two
identical amplifiers (Figure 1). Each amplifier has an enable pin (ENA and ENB). When both
amplifiers are enabled, the LT5514 operates in “standard” (full power-high intercept point mode). The
low power mode is selected when only one amplifier is enabled. Four programmable gain inputs
provide a variable attenuation of up to 22.5 dB (relative to maximum gain) with 1.5 dB steps.
Gain control logic Enable control
Am
p
A
Amp B
Attenuator
Figure 1. LT5514 Block Diagram
DC550A Demo Board
Quick Start Guide 1
DEMO BOARD CONFIGURATIONS
DEMO BOARD RF INPUT:
TYPE RF Input: Input
Impedance
1dB Freq. Range
Notes
A SINGLE ENDED 50 ohms 3 – 300 MHz
(Limited by RF input
transformer)
1:2 RF Input
Transformer
B DIFFERENTIAL 100 ohms
Differential
.1 – 600 MHz Capacitive
Coupled
In
p
ut RF Transformer
Gain control logic Enable control
Amp A
Amp B
Variable
Attenuator
Type A Input
Type B Input
Gain control logic Enable control
Amp A
C
Amp B
Variable
Attenuator
C
DC550A Demo Board
Quick Start Guide 2
DEMO BOARD RF OUTPUT:
TYPE RF Output: Output
Impedance
1dB Freq. Range
Max
Gain
Notes
A DIFFERENTIAL 100 ohms
Differential
.1 – 600 MHz 27dB Capacitive
Coupled
B SINGLE ENDED 50 ohms
Single Ended
10 – 200 MHz
(Limited by RF
output transformer )
30dB 4:1 RF
Output
Transformer
Vcc
Type A Output
50
ohm
50
ohm
Gain control logic Enable control
Amp A
Amp B
Variable
Attenuator
RF Output
Transformer
255 ohm
Gain control logic Enable control
Amp A
Amp B
Variable
Attenuator
Vcc
Type B Output
C
C
DC550A Demo Board
Quick Start Guide 3
NOTE: LT5514 Demo circuits have been provided with Type A input configuration
and with Type B output configuration, (RF transformers at input & output ports).
RF Output
Transformer
R7
255 ohm
Gain control logic Enable control
Amp A
LT5514
Amp B
Variable
Attenuator
Vcc
Input RF Transformer
Figure 2. Block Diagram of the DC550A Demo Circuit with Type A Input and with
Type B Output Configuration.
Please refer to the next page for actual electrical schematic of the LT5514 IC demo board DC550A
with a Type A input and with a Type B output. Please note C2, C3, C7, C8, C11, C12 are not
placed on PCB, as well as some Vcc bypass capacitors and D1 Zener diode.
Also enclosed, as a separate document, a complete demo board schematic and parts list, which
support all possible configurations and modifications for the demo board.
Please note that with R7 (255 ohm, differential output shunt resistor), the circuit provides the best
output return loss. For the best IM3 performance this resistor should be removed, resulting in about
3 dB IP3 improvements. This will also result in a small degradation of the return loss.
DC550A Demo Board
Quick Start Guide 4
DC550A Demo Board
Quick Start Guide 5
Demo Circuit Settings (refer to demo board schematic):
Table 1. Modes of Operation
Modes EN_A EN_B
Amp A Amp B LT5514 State
1 Standard
(Full Power)
HIGH HIGH ON ON Enable amp A and amp B
2 Low Power A HIGH LOW ON OFF Enable amp A
3 Low Power B LOW HIGH OFF ON Enable amp B
4 Shutdown LOW LOW OFF OFF Sleep, both amps disabled
Note: Enable inputs ENA and ENB can be controlled externally using turret pins ENA and ENB
located at the top of the demo board. HIGH logic levels are provided to both Enable inputs by
default (because of the pull-up resistors on the control lines).
Table 2. Gain Programming Table
ATTENUATION
Relative to MAX GAIN
PGA0 PGA1
PGA2 PGA3
1 0 dB HIGH HIGH HIGH HIGH
2 -1.5 dB LOW HIGH HIGH HIGH
3 -3.0 dB HIGH LOW HIGH HIGH
4 -4.5 dB LOW LOW HIGH HIGH
5 -6.0 dB HIGH HIGH LOW HIGH
6 -7.5 dB LOW HIGH LOW HIGH
7 -9.0 dB HIGH LOW LOW HIGH
8 -10.5 dB LOW LOW LOW HIGH
9 -12.0 dB HIGH HIGH HIGH LOW
10 -13.5 dB LOW HIGH HIGH LOW
11 -15.0 dB HIGH LOW HIGH LOW
12 -16.5 dB LOW LOW HIGH LOW
13 -18.0 dB HIGH HIGH LOW LOW
14 -19.5 dB LOW HIGH LOW LOW
15 -21.0 dB HIGH LOW LOW LOW
16 -22.5 dB LOW LOW LOW LOW
Note: Gain control lines PGA0, PGA1, PGA2 and PGA3 can be controlled externally using pins
PGA0, PGA1, PGA2 and PGA3 located at the bottom of the demo board.
HIGH logic levels are provided to all four gain control inputs by default (pull-up resistors on the
control inputs).
DC550A Demo Board
Quick Start Guide 6
LPF
Signal
Generator #1
J2
J4
GND
Signal
Generator #2
Spectrum
Analyzer
Power
Supply
PGA0 PGA1 PGA2 PGA3 GND
J1
J3
LT5514EFE
GND GND VCC ENA ENB VCCO
LPF
2-way
Combiner
Figure 3. Test & Measurement Setup for Single Ended Input & Single Ended Output Demo
Circuit.
DC Power Consumption Measurements:
Connect test equipment and power supply to the demo board as shown in Figure 3.
Set power supply to +5.0V.
NOTE: For a demo board with a type “A” output (with 50 ohm pull-up resistors) a separate 7.5V
power supply should be connected to Vcco for measurements with output signal swing of 2.0V peak
to peak or higher. This will result in 5.0VDC at the output (open collector) pins, because of the
voltage drop across the 50 ohm output pull-up resistors.
Shutdown Mode: Set ENA and ENB to Logic LOW state.
Measure VCC and VCCO shutdown current.
NOTE: Shutdown current should be 1 to 2mA due to external
10k ohm pull-up resistors (R8 and R9).
Standard Operation Mode: Set ENA and ENB to Logic HIGH state.
Measure VCC and VCCO operating current.
DC550A Demo Board
Quick Start Guide 7
Gain, Frequency Response and OIP3 Measurements:
1) Connect test equipment and power supply to the demo board as shown in Figure 3.
2) Set ENA and ENB to Logic HIGH state (Refer to Table 1 and Table 2). The IC is in Standard
Operation Mode (both amps are ON) and the amplifier has maximum gain.
3) Perform single CW tone frequency sweep (100 KHz to 600 MHz) and measure gain and
frequency response. NOTE: For a demo board with a type “A” output (with 50 ohm pull-up
resistors) external 180o combiner should be used. Measurements can be also done using one
output. In this case the other output should be terminated externally. One-output measurements
have no common mode rejection and will show higher output noise.
4) Apply two input CW tones and perform two-tone output IM3 product measurements at different
output power levels from 0 dBm to +10 dBm (per each tone).
NOTE: For a demo board with a type “A” output (with 50 ohm pull-up resistors) an external
180o combiner should be used. Single output measurements will show an elevated noise floor.
For single output measurements, the second output should be terminated externally with 50 ohm
load.
Notes for Two Tone Measurements:
1. High quality signal generators (with low level of output harmonics and reverse power
protection) should be used. Low pass filters should be employed at the signal generator outputs
to minimize higher order harmonics to –90 dBc or better. Attenuator pads at the signal generator
outputs will also help to minimize reverse power problems.
2. A high sensitivity/high dynamic range spectrum analyzer should be used. Care must be taken to
operate the spectrum analyzer in linear mode to avoid additional IM distortion products
produced by the instrument itself. It is advisable to use a narrow bandpass filter at the spectrum
analyzer input to select IM products and attenuate main tones. In this case, a 10 to 20 dB
attenuator should be placed between the LT5514 output and the BPF input to provide broadband
matching.
Additional application notes (refer to the complete demo circuit schematic):
In a type “B” output (demo circuit with output RF transformer), resistor R7 is 255 ohm. This
provides the best output return loss. For best IM performance this resistor should be removed.
This will result in a 5dB IM3 performance improvement.
R19 is a zero ohm jumper. R19 can be removed if differential output is desired.
Output transformer T2 can be removed and pull-up resistors (50 ohm) can be placed at R20 and
R21 locations at the topside of the demo board. Also, pull-up inductors (820 nH) can be placed
at R20 and R21 locations as well. This will result in higher output impedance. For proper
impedance matching 50 ohm resistors can be connected in parallel with pull-up inductors.
Coupling capacitors (not shown on the demo board schematic) can be placed instead of the
output transformer T2, connecting output pins 15 and 16 to the output SMA connectors J2 and
J4.
DC550A Demo Board
Quick Start Guide 8
DC550A Demo Board
Quick Start Guide 9
DC550A Demo Board
Quick Start Guide 9