Linear Technology DC1418A-A User manual

DEMO CIRCUIT 1418 QUICK START GUIDE LTC6604-X
1
DESCRIPTION
Demonstration circuit 1418 features the LT6604-XX se-
ries of a dual, matched, fully differential 4
th
order low-
pass filter approximating a Chebyshev frequency re-
sponse
. The cutoff frequencies (Fc) of LT6604-XX are:
2.5MHz, 5MHz, 10MHz and 15MHz. (see Table 1). The
LT6604-XX combines a lowpass filter with two fully
differential matched amplifiers for driving the differ-
ential inputs of a dual analog to Digital Converter
(ADC) and band-limiting the baseband signal of digi-
tal communications receiver. Each LT6604-XX filter IC
requires only two external input resistors to set the fil-
ter’s differential gain. A DC1418 board contains an
LT6604-XX configured with input resistors as two unity
gain differential amplifiers/lowpass filters.
ries of a dual, matched, fully differential 4
th
order low-
pass filter approximating a Chebyshev frequency re-
sponse
. The cutoff frequencies (Fc) of LT6604-XX are:
2.5MHz, 5MHz, 10MHz and 15MHz. (see Table 1). The
LT6604-XX combines a lowpass filter with two fully
differential matched amplifiers for driving the differ-
ential inputs of a dual analog to Digital Converter
(ADC) and band-limiting the baseband signal of digi-
tal communications receiver. Each LT6604-XX filter IC
requires only two external input resistors to set the fil-
ter’s differential gain. A DC1418 board contains an
LT6604-XX configured with input resistors as two unity
gain differential amplifiers/lowpass filters.
Gains greater than one require changing the input resis-
tors to a lower value (refer to an LTC6604-XX data sheet
and the DC1418 schematic).
Gains greater than one require changing the input resis-
tors to a lower value (refer to an LTC6604-XX data sheet
and the DC1418 schematic).
Connection to the differential input and output of a
DC1418 is through SMA connectors. On-board jumpers
configure the DC1418 for dual or single supply opera-
tion and internal or external output common (VOCM)
mode biasing. The differential input of a DC1418 is AC
coupled and can be configured for DC coupling by re-
placing shorting the input capacitors with zero ohms
surface-mount resistor jumpers. In addition, the
DC1418 has surface-mount pads to add input passive
components for input signal filtering and DC biasing.
Connection to the differential input and output of a
DC1418 is through SMA connectors. On-board jumpers
configure the DC1418 for dual or single supply opera-
tion and internal or external output common (VOCM)
mode biasing. The differential input of a DC1418 is AC
coupled and can be configured for DC coupling by re-
placing shorting the input capacitors with zero ohms
surface-mount resistor jumpers. In addition, the
DC1418 has surface-mount pads to add input passive
components for input signal filtering and DC biasing.
Design files for this circuit board are available.Design files for this circuit board are available.
Call the LTC factory.Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
DEMO CIRCUIT 1418
QUICK START GUIDE
LTC6604-2.5, LTC6604-5, LTC6604-10 and LTC6604-15
Dual, Matched, Fully-Differential, Lowpass Filter
ASSEMBLY
DC1418A-A LTC6604-2.5, Fc = 2.5MHz
DC1418A-B LTC6604-5, Fc = 5MHz
DC1418A-C LTC6604-10, Fc = 10MHz
DC1418A-D LTC6604-15, Fc = 15MHz
Table 1. The DC1418 Assemblies
Figure 1. The DC1418 Top Silk Screen

DEMO CIRCUIT 1418 QUICK START GUIDE LTC6604-X
QUICK TEST SET UP
2
Quick Test Procedure
A DC1418 has two pairs of differential inputs,
Vin+A/Vin-A and Vin+B/Vin-B and two pairs of differen-
tial outputs Vout-A /Vout+A and Vout-B/Vout-B.
1. Testing the VinA to VoutA Signal Path.
Connect a DC1418 board as shown in Figure 2 (connect
signal generator to Vin+A and terminate Vin-A with a 50
ohm terminator). Set the generator for a 1MHz, 2Vp-p,
and sinewave. The oscilloscope channels connected to
Vout-A and Vout+A show a 1MHz, 1Vp-p, sinewave (see
Note 1).
Dual Power Supply
Oscilloscope (≥100MHz)
2. Testing the VinB to VoutB Signal Path.
Connect signal generator to Vin+B and terminate Vin-B
with a 50 ohm terminator. Set the generator for a 1MHz,
2Vp-p, and sinewave. Connect oscilloscope channel 1 to
Vout-B and channel 2 to Vout+B. The oscilloscope
channels connected to Vout-B and Vout+B show a
1MHz, 1Vp-p, sinewave.
Note 1: For unity gain testing the DC1418 inputs must
be ideally driven by a zero ohm source (the outputs of a
high speed differential amplifier). However with the 50
ohm impedance of the generator’s output and termina-
tor is in series with the input resistors and the input to
output gain is less than one.
Note 2: For single supply testing set the JP2 shunt to
SINGLE.
Signal Generator
with 50 Ohm Out
p
ut
50 Ohm
Terminator
Figure 2. Dual Supply Test Set Up Connections
(set the JP1 shunt to VMIDA and the JP2 shunt to DUAL).

DEMO CIRCUIT 1418 QUICK START GUIDE LTC6604-X
3

DEMO CIRCUIT 1418 QUICK START GUIDE LTC6604-X
DC1418A General Parts List
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