FAQ: What is the latency of the AD9789?

Document created by danf Employee on Jul 5, 2011Last modified by AndyR on Jan 31, 2012
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Q.

What is the latency of the AD9789?

 

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A.

Define latency as the elapsed time from a sample clocked at the input to the AD9789 until the analog output begins changing. The latency of the AD9789 depends on which digital blocks are enabled in the datapath. The time can be approximated by using the calculation method provided below.

 

For each block in the table below that is enabled, take the latency number, and multiply it by the period of the clock listed in the units column to determine the latency through that block.  Sum all of the calculated latencies together to determine the latency through the device.  This method is not exact, but the approximation is sufficient for most applications.

 

block    latency    units

input       1           BR

QAM       1          BR

SRRC     44         BR/2

2x0        28         BR/4

2x1        13         BR/8

2x2        10         BR/16

2x3         5          BR/32

2x4         5          BR/64

RC          6          FS*16

DDS        5          FS*16

sum        3           FS*16

16x     144           FS

 

BR = period of baud rate clock

FS = period of DAC clock

 

Note that the highest latency values are calculated for those blocks that run at or close to the baud rate.

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