DC807A - Demo Manual

December 03, 2004
Demo Circuit DC807A Quick Start Guide.
Introduction
Demo circuit DC807A demonstrates operation of the LT5524 IC, a DC-600MHz bandwidth ‘open
loop’ transconductance amplifier with high impedance ‘open collector’ outputs. Four programmable
gain inputs provide a variable attenuation of up to 22.5 dB (relative to maximum gain) with 1.5 dB
steps.
LT5524
Attenuator
Amp
Gain control logic
Enable control
Figure 1. LT5524 Block Diagram
DEMO BOARD CONFIGURATIONS
DEMO BOARD RF INPUT:
TYPE
RF Input:
A
SINGLE ENDED
B
DIFFERENTIAL
DC807A Demo Board
Quick Start Guide
Input
Impedance
50 ohms
100 ohms
Differential
1dB Freq. Range
Notes
3 – 300 MHz
(Limited by RF input
transformer)
.1 – 600 MHz
1:2 RF Input
Transformer
Capacitive
Coupled
1
Type A Input
LT5524
Input RF Transformer
Variable
Attenuator
Amp
Gain control logic
Enable control
Type B Input
LT5524
C
Variable
Attenuator
Amp
C
Gain control logic
DEMO BOARD RF OUTPUT:
TYPE
RF Output:
A
DIFFERENTIAL
B
SINGLE ENDED
DC807A Demo Board
Quick Start Guide
Output
Impedance
100 ohms
Differential
50 ohms
Single Ended
Enable control
1dB Freq. Range
.1 – 600 MHz
Max
Gain
24dB
10 – 200 MHz
24dB
(Limited by RF
output transformer )
Notes
Capacitive
Coupled
4:1 RF
Output
Transformer
2
Vcc
Type A Output
50
ohm
50
ohm
LT5524
C
Variable
Attenuator
Amp
C
Gain control logic
Enable control
Type B Output
Vcc
LT5524
Variable
Attenuator
RF Output
Transformer
Amp
255 ohm
Gain control logic
Enable control
NOTE: LT5524 Demo circuits have been provided with Type A input configuration
and with Type B output configuration, (RF transformers at input & output ports).
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Quick Start Guide
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LT5524
Amp A
Vcc
Input RF Transformer
Variable
Attenuator
Gain control logic
RF Output
Transformer
Amp B
Enable control
R7
255 ohm
Figure 2. Block Diagram of the DC807A Demo Circuit with Type A Input and with
Type B Output Configuration.
Please refer to the next page for actual electrical schematic of the LT5524 IC demo board DC807A
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.
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Quick Start Guide
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Demo Circuit Settings (refer to demo board schematic):
Table 1. Modes of Operation
Modes
1 Full Power
2 Shutdown
EN
HIGH
LOW
LT5524 State
Amplifier enabled
Sleep, amplifier disabled
Note: Enable input EN can be controlled externally using turret pins EN located at the top of the
demo board. HIGH logic level is provided to Enable input by default (because of the pull-up resistor
on the control line).
Table 2. Gain Programming Table
ATTENUATION
PGA0
Relative to MAX GAIN
1
0 dB
HIGH
2
-1.5 dB
LOW
3
-3.0 dB
HIGH
4
-4.5 dB
LOW
5
-6.0 dB
HIGH
6
-7.5 dB
LOW
7
-9.0 dB
HIGH
8
-10.5 dB
LOW
9
-12.0 dB
HIGH
10
-13.5 dB
LOW
11
-15.0 dB
HIGH
12
-16.5 dB
LOW
13
-18.0 dB
HIGH
14
-19.5 dB
LOW
15
-21.0 dB
HIGH
16
-22.5 dB
LOW
PGA1
PGA2
PGA3
HIGH
HIGH
LOW
LOW
HIGH
HIGH
LOW
LOW
HIGH
HIGH
LOW
LOW
HIGH
HIGH
LOW
LOW
HIGH
HIGH
HIGH
HIGH
LOW
LOW
LOW
LOW
HIGH
HIGH
HIGH
HIGH
LOW
LOW
LOW
LOW
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
LOW
LOW
LOW
LOW
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).
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Quick Start Guide
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LPF
Signal
Generator #1
2-way
Combiner
LPF
Signal
Generator #2
Power
Supply
GND
ENA
VCC
VCCO
GND
Spectrum
Analyzer
LT5524EFE
J1
J2
J3
J4
GND
PGA0
PGA1
PGA2
PGA3
GND
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 EN to Logic LOW state.
Measure VCC and VCCO shutdown current.
NOTE: Shutdown current should be 0.5 to 1mA due to
external 10k ohm pull-up resistor.
Set EN to Logic HIGH state.
Operation Mode:
Measure VCC and VCCO operating current.
Gain, Frequency Response and OIP3 Measurements:
1) Connect test equipment and power supply to the demo board as shown in Figure 3.
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Quick Start Guide
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2) Set EN to Logic HIGH state (Refer to Table 1 and Table 2). The IC is in Standard Operation
Mode (amplifier is 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 -23 dBm to 0 dBm per each tone, referred to the input of the demo
board and depending on desired attenuation settings.
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.
Two Tone Measurements (refer to “LT5514 linearity measurements” document):
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 LT5524 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.
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Quick Start Guide
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Quick Start Guide
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