QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1164
SIGNAL SOURCE
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High Speed ADC Signal Source
DESCRIPTION
Demonstration circuit 1164 is a signal source to
use to demonstrate high speed ADCs. Each as-
sembly will include a 70.56MHz crystal which can
be used with any high speed ADC as a clean signal
source.
Functionally, the DC1164 uses a crystal oscillator as
a precision clock source. The output of the crystal
is then directed through a signal chain which pro-
vides proper filtering to produce a low distortion,
low noise signal tone signal for high speed ADCs.
A programmable step attenuator allows for 32dB of
dynamic range on the output signal.
By replacing a few components and a jumper, this
demo board becomes a complete IF strip for use
with spread spectrum signals. By feeding this
board with an external spread spectrum signal, the
signal chain becomes a means to provide a clean
low noise signal, with programmable amplitude, to
the ADC.
This circuit also is a model for designing complex IF
strips which require SAW filtering and multiple am-
plifiers. Design files for this circuit board are
available. Call the LTC factory.
LTC is a trademark of Linear Technology Corporation
Table 1.
Performance Summary (T
A
= 25°C)
PARAMETER CONDITION VALUE
Supply Voltage
The board has LT1763 LDOs
to provide power to the vari-
ous parts of the circuit.
6V-9V
Crystal frequency 70.56MHz
Saw Filter Bandwidth 20MHz
Saw Filter Center Fre-
quency 70MHz
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1164
SIGNAL SOURCE
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QUICK START PROCEDURE
Demonstration circuit 1152 is easy to set up to evaluate
the performance of most members of the LTC2246H
family of A/D converters. Refer to Figure 1 for proper
measurement equipment setup and follow the procedure
below:
SETUP
JUMPERS:
Signal Path/Xtal – Selects which element is active.
Xtal supplies the crystal with 5 volts, producing a
70.56MHz signal at the output. Signal path removes
the 5 volts on the crystal and redirects it to the gain
block to amplify the external signal presented at J1.
-0dB/-16dB – Provides an additional 16dB of at-
tenuation. Selecting 0dB provides attenuation from
0dB to 16dB, and -16 provide attenuation from16dB
to 32dB.
SW1 - A rotary switch that controls attenuation in
1 dB steps. The “0” setting is 0dB of attenuation,
and “F” is 16dB of attenuation.
PORTS:
J1: Signal input – When using the DC1164 as an IF
strip J1 is where to input the signal
J2: Signal Output – Outputs the filtered signal. Con-
nect this port to the analog input of the ADC demo
board.
J3: Clock Output – For applications where a clock sig-
nal is required, use this port as a reference clock. This
is not to be used as a clock for the ADC.
6-9V
+
-
Signal Output
To ADC Demo Board
Signal Input
Clock Ou
t
put
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1164
SIGNAL SOURCE
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POWER
The DC1164 requires a voltage between 6 and 9 volts.
This voltage is then post regulated to provide for all
other required voltages on the board. The power sup-
ply used should be able to provide 500mA. If power is
applied a green LED should illuminate. If power is ap-
plied in reverse the LED will be red.
70.56MHZ SIGNAL SOURCE
In standard operation J2 should provide a 70.56MHz
signal to the demo board. The only connections re-
quired in this mode are power, and the output SMA
(J2) connected to ADC demo board. The signal ampli-
tude should be close to full scale and the signal ampli-
tude can be controlled by SW1 and the adjacent
jumper. The switch has 16 positions corresponding
with 1 dB steps in attenuation of the signal. Zero “0”
being no attenuation, and “F” being 16 dB of attenua-
tion. The jumper adjacent to the switch can provide an
additional 16 dB of attenuation added to the switch
setting. This gives a maximum of 32 dB of attenuation
on the signal.
IF STRIP
By removing C37, stuffing C40 and C41 and moving
the jumper Xtal to Signal Path, the DC1164 becomes
an IF strip which can provide low distortion spread
spectrum signals to an ADC demo board. Connect an
external spread spectrum source to J1, and connect
the DC1164 to a ADC demo board.
The DC1164 has a signal path that has been matched
and optimized for signals from 60MHz to 80MHz. The
center frequency of the SAW filter is 70MHz and it has
a 20MHz bandwidth. All of the amplifiers used are
also tuned for frequencies between 60MHz and
80MHz.
The input signal can be attenuated to a spefic power
level by using SW1 and the adjacent jumper. For SW1
Zero “0” causes no attenuation, and “F” is 16dB of
attenuation. Turning the switch clockwise causes 1dB
steps of attenuation up to 16dB. The adjacent jumper
gives an additional 16dB of attenuation when moved
from 0dB to -16dB.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1164
SIGNAL SOURCE
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