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dc1281af
DEMO MANUAL DC1281A
QUICK START PROCEDURE
Applying Power and Signals to the DC996
Demonstration Circuit
If a DC890 is used to acquire data from the DC1281A, the
DC890 must
first
be connected to a powered USB port
or provided an external 6V to 9V
before
applying 3.3V or
3.6V across the pins 3.3V and PWR GND on the
DC1281A. The LTC2209#3BC and LTC2209#3CD require
3.6V for proper operation. The DC1281A demonstration
circuit requires up to 700mA depending on the sampling
rate and the A/D converter supplied.
The DC890 data collection board is powered by the USB
cable and does not require an external power supply unless
it must be connected to the PC through an unpowered hub
in which case it must be supplied an external 6V to 9V on
turrets G7(+) and G1(–) or the adjacent 2.1mm power jack.
Analog Input Network
For optimal distortion and noise performance the RC
network on the analog inputs may need to be optimized
for different analog input frequencies. For input frequen-
cies above 160MHz use demonstration circuit 1281A.
Other input networks may be more appropriate for input
frequencies less that 5MHz.
In almost all cases, filters will be required on both analog
input and encode clock to provide data sheet SNR.
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: This is not a logic-compatible input. It is terminated
with 50Ω.
Apply an encode clock to the SMA connector
on the DC1281A demonstration circuit board marked
J7 ENCODE INPUT. This is a transformer-coupled input,
terminated on the secondary side in two steps, 100Ω at
the transformer with final termination at the ADC at 100Ω.
For the best noise performance, the ENCODE INPUT must
be driven with a very low jitter source. When using a si-
nusoidal generator, the amplitude should often be as large
as possible, up to 3V
P-P
or 15dBm. Using bandpass filters
on the clock and the analog input will improve the noise
performance by reducing the wideband noise power of the
signals. 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 genera-
tors 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 connec-
tors on the DC1281A demonstration circuit board marked
J5 ANALOG INPUT. These inputs are capacitive coupled to
Balun transformers ETC1-1-13, or directly coupled through
Flux-coupled transformers ETC1-1T.
An internally generated conversion clock output is available
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 QuikEval II
Data Acquisition Board using PScope™ software.
Software
The DC890 is controlled by the PScope system software
provided or downloaded from the Linear Technology
website at
http://www.linear.com/software/
. If a DC890
was provided, follow the DC890 Quick Start Guide and
the instructions below.
To start the data collection software if PScope.exe is in-
stalled (by default) in \Program Files\LTC\PScope\, double
click the PScope icon or bring up the run window under
the start menu and browse to the PScope directory and
select PScope.
