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.
Amp A
Attenuator
Amp B
Gain control logic
Enable control
Figure 1. LT5514 Block Diagram
DC550A Demo Board
Quick Start Guide
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NOTE: LT5514 Demo circuits have been provided with Type A input configuration
and with Type B output configuration, (RF transformers at input & output ports).
LT5514
Amp A
Vcc
Input RF Transformer
Variable
Attenuator
Amp B
R7
255 ohm
RF Output
Transformer
Gain control logic
Enable control
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
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