Linear Technology DC1369A Demo Manual page 4

DEMO MANUAL DC1369A
Quick start proceDure
In almost all cases, filters will be required on both analog
input and encode clock to provide data sheet SNR. In the
case of the DC1369A a bandpass filter used for the clock
should be used prior to the DC1075A.
The filters should be located close to the inputs to avoid
reflections from impedance discontinuities at the driven
end of a long transmission line. Most filters do not present
50Ω outside the passband. In some cases, 3dB to 10dB
pads may be required to obtain low distortion.
If your generator cannot deliver full-scale signals without
distortion, you may benefit from a medium power amplifier
based on a Gallium Arsenide Gain block prior to the final
filter. This is particularly true at higher frequencies where
IC based operational amplifiers may be unable to deliver
the combination of low noise figure and High IP3 point
required. A high order filter can be used prior to this final
amplifier, and a relatively lower Q filter used between the
amplifier and the demo circuit.
Encode Clock
NOTE: Apply an encode clock to the SMA connector on
the DC1369A demonstration circuit board marked J7.
As a default the DC1369A is populated to have a single-
ended input.
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For the best noise performance, the encode input must
be driven with a very low jitter, square wave source. The
amplitude should be large, up to 3V
using a sinusoidal signal generator a squaring circuit can
be used. Linear Technology also provides demo board
DC1075A that divides a high frequency sine wave by four,
producing a low jitter square wave for best results with
the LTC2262 family.
Using bandpass filters on the clock and the analog input
will improve the noise performance by reducing the
wideband noise power of the signals. In the case of the
DC1369A a bandpass filter used for the clock should be
used prior to the DC1075A. Data sheet FFT plots are taken
with 10 pole LC filters made by TTE (Los Angeles, CA) to
suppress signal generator harmonics, non harmonically
related spurs and broadband noise. Low phase noise Agilent
8644B generators are used with TTE bandpass filters for
both the clock input and the analog input.
Apply the analog input signal of interest to the SMA con-
nectors on the DC1369A demonstration circuit board
+
marked J5 A . These inputs are capacitive coupled to
IN
Balun transformers ETC1-1-13.
An internally generated conversion clock output is avail-
able on J1 which could be collected via a logic analyzer, or
other data collection system if populated with a SAMTEC
MEC8-150 type connector or collected by the DC890 Qui-
kEval II Data Acquisition Board using PScope™ software.
or 13dBm. When
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