Analog Devices Linear Technology DC2085 Demo Manual page 5

QUICK START PROCEDURE
ANALOG OUTPUT NETWORK
The analog output network of the DC2085 has been
designed to maximize the performance of the LTC2000.
The LTC2000 drives two 50Ω resistors on each side to
minimize the impedance it sees. This maximizes the SFDR
the DAC is able to produce. If a larger signal swing is
required this impedance can be increased, but the SFDR
might degrade. The output also has a pi network of 50Ω
resistors to pad the output impedance of the board up to
50Ω per side. This allows the demo board to drive a 50Ω
analyzer through a balun or other combiner.
Linear Technology has various coupon boards for specific
frequencies and applications. More information is available
at www.linear.com.
SAMPLE CLOCK
The sample clock to the DC2085 demonstration circuit
board is marked J4. As a default it is a single-ended 50Ω
input port. There is an onboard balun that does a single-
ended to differential translation.
DEMO MANUAL DC2085
For the best noise performance, the sample input must
be driven with a very low jitter signal generator source.
The amplitude should be as large as possible up to ±1.8V
or 9dBm.
SOFTWARE
The software for the DC2085, LTDACGen is available at
www.linear.com
of complex waveforms and loading them into the FPGA to
test the DC2085. For more information about how to use
the LTDACGen software, refer to the help files that come
with the software.
RESULTS
After everything is set up and the software is con-
nected to the DAC demo system, a sine wave can be
added to the output waveform. The default frequency is
399.932861328MHz (Figure 3). By clicking Update FPGA,
the data is sent to the FPGA and is then used to program
the DAC. A spectrum analyzer can then be used to view
the results (Figure 4).
Figure 3. Default Frequency
free of charge. It simplifies the creation
dc2085afb
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