DEMO CIRCUIT DC1147 QUICK START GUIDE
LOW NOISE/DISTORTION 16-BIT DIFFERENTIAL ADC DRIVERS
1
DESCRIPTION
Demonstration circuit 1147 features the LTC6404-x,
LTC6406, LTC6403-1, and LTC6405 16-bit ADC Drivers. It
incorporates a variety of passive components to support
configurations for varied applications. Single-ended or dif-
ferential input and output configurations are possible, and
there is a calibration circuit to null out the effects of other
circuit components.
The LTC640x are high-speed differential amplifiers with su-
perior distortion and noise performance, perfect for de-
manding communications transceivers, cellular base-
stations, and other high-speed signal chain applications.
These fully-differential amplifiers accept single-ended or
differential inputs with almost no difference in distortion
performance. Each part has the ability to independently ad-
just the output common-mode voltage without any addi-
tional components, and flexible input common-mode
ranges which enable level-shifting of input signals for ADC
driving applications.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
QUICK START PROCEDURE
Table 1 shows the function of each SMA connector on the
board. Refer to Figure 1 for the connection diagram and
follow the procedure below:
1.
Connect the power supply as shown. The power labels of
V+, VOCM, and GND directly correspond to the power
supply and VOCM pins of the LTC640x ICs (U1). Jumper
JP1 enables or shuts down the amplifier.
2.
The power supplies available for each part are shown in
Table 1.
Do not exceed the maximum power supply
voltage for the parts.
3.
Apply an input signal to J1. A low-distortion, low
noise signal source with an external high-order filter
will yield the best performance. DC1147’s input is
impedance-matched to 50Ω; no external termination
is necessary.
4.
Observe the output via J3. The output is impedance-
matched to 50Ω, suitable for the input of a network or
spectrum analyzer.
Table 1: DC1147 Board I/O Descriptions
CONNECTOR FUNCTION
J1 (IN+) Differential Input. Use this connector to supply an input
to the DC1147. Drive from a 50ohm signal source, no
external termination necessary.
J2 (OUT-) Differential Output. Not connected by default. Resistor
R9 can installed and R10 removed to receive the output
signal differentially.
J3 (OUT+) Output. Impedance-matched to 50 ohms, can be used
to drive a 50ohm network/spectrum analyzer input.
J4 (IN-)
Differential Input. Not connected by default. Resistor
R24 can be installed and R27 removed for differential
input drive. R4 and R7 should be matched or both re-
moved to provide a balanced input impedance.
JP1 (SHDN) Shutdown jumper. The left (EN) position enables the
part, while the right (DIS) puts it into shutdown mode.
E3 (VOCM) Output Common-Mode Adjust. By default, this pin is
self-biasing within U1. Override this voltage with any
DC voltage source.
E5 (VTIP) Corresponds to the VTIP pin in DC1147-D
(LTC6405/6). Consult the datasheet for pin function.
Leave floating if unused. This pin is not connected for
all the other parts in the family.
DEMO CIRCUIT
1147
QUICK START GUIDE
LTC6404-
x, LTC6406,LTC6405
and LTC6403-
1
16-
Bit Differential ADC Drivers
DEMO CIRCUIT DC1147 QUICK START GUIDE
LOW NOISE/DISTORTION 16-BIT DIFFERENTIAL ADC DRIVERS
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ADDITIONAL INFORMATION
Although the DC1147 demo board is ready to use out of
the box, it has features that you can access by adding, re-
moving or changing components on the board. These are
described below.
DEMO BOARD VERSIONS
DC1147 has four versions to support all of the pin-
compatible parts in the LTC640x amplifier family. Table 1
contains a listing of the different amplifiers and their supply
voltage ranges. See the schematic (on the last page of this
guide) for component differences between the versions.
DEMO BOARD SUPPLY VOLTAGES
Table 2: DC1147 Supply Voltages
DEMO
BOARD
U1 SUPPLY VOLTAGE RANGE
DC1147A-A LTC6404-1 2.7-5.25V
DC1147A-B LTC6404-2 2.7-5.25V
DC1147A-C LTC6404-4 2.7-5.25V
DC1147A-D LTC6406 2.7-3.5V
DC1147A-E LTC6403-1 2.7-5.25V
DC1147A-F LTC6405 2.7-5.25V
DIFFERENTIAL INPUTS
To drive the inputs differentially, remove resistor R27 and
install R24. J1 and J4 can now be driven differentially from
a 50Ω signal source. R4 and R7 should be changed to dif-
ferentially match the input to 50Ω if necessary.
DRIVING THE INPUTS DC-COUPLED
It is possible to drive the DC1147 inputs differentially with
DC coupling. Transformer T1 should be replaced with 0Ω
resistors. The inputs are now DC-coupled and can be dri-
ven single-ended or differentially (resistor values may be
changed to balance the source impedances, et cetera. See
Figure 1: Proper Measurement Equipment Setup
DEMO CIRCUIT DC1147 QUICK START GUIDE
LOW NOISE/DISTORTION 16-BIT DIFFERENTIAL ADC DRIVERS
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the product datasheets for more information. Input bias
currents will flow through the amplifier’s input resistors if
DC1147 is driven DC coupled.
DIFFERENTIAL OUTPUTS
To use the both outputs of the DC1147, remove resistor
R10 and install R9. The output now appears differentially
across J3 and J2. The output of the DC1147 will still be
matched to 50Ω (differentially) when used in this manner.
CHANGING THE OUTPUT COMMON-MODE VOLTAGE
Turret E3 controls the output common-mode voltage of U1.
This function can be used to level-shift the DC output volt-
age for optimum system performance. If used for this pur-
pose, transformer T2 can be replaced by 0Ω resistors to
allow the DC bias to reach the output. By default, the VOCM
voltage is self-biased through resistors internal to the IC’s
(U1).
OUTPUT DRIVE
Since the output of the LTC6400/1 is a low-impedance op-
erational amplifier output, performance will degrade when
the output is directly driving low impedances such as 50Ω.
On DC1147 there are series 100 ohms resistors at the out-
put as well as a 4:1 transformer to increase the load im-
pedance seen by the amplifier.
ENABLE (SHUTDOWN)
Jumper JP1 controls the enable function of DC1147. When
set to the EN position, the part will be on and draw quies-
cent current. In the DIS position, the part will be in shut-
down and draw a very small amount of quiescent current.
GROUND AND VCC CONNECTIONS
DC1147’s GND connector is not only connected to V- of
the LTC640x, it also serves as the board ground. For best
performance, a low-impedance return path to the power
supply from GND is crucial. Short, low impedance wires to
the V+ and GND connectors of DC1147 will yield the best
performance from the LTC6400/1.
SCHEMATIC NOTES
Note that transformer T2 and the series resistors at the
amplifier outputs create a 12.6dB attenuation (if the output
has a 50Ω load) that will affect the measured gain of the
demo board. This is done so that the output of DC1147 can
plug directly into a 50Ω network/spectrum analyzer input,
but the amplifier sees a higher 400Ω load impedance.
DEMO CIRCUIT DC1147 QUICK START GUIDE
LOW NOISE/DISTORTION 16-BIT DIFFERENTIAL ADC DRIVERS
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