GC5016 Datasheet, PDF (21/88 Pages) Texas Instruments – WIDEBAND QUAD DIGITAL DOWN CONVERTER/ UP CONVERTER

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GC5016
SLWS142G − JANUARY 2003 − REVISED NOVEMBER 2005
Number_of_clocks = cic_dec x fir_dec
If the data stream is complex, then half the clock cycles are used computing the I output and half are used computing
the Q output. The tap delay line limits the filter length to 256 if non-symmetric and 512 if symmetric (half this with
complex data streams). The maximum number of taps is determined by the cmd5016 program. It can be estimated
by:
ntaps = sym x 16 x fir_dec x int(min(cic_dec,16/fir_dec)/(cmplx/fir_nchan)) − odd
Where:
cmplx = 1 for real data (or splitiq) and 2 for complex
sym = 1 for nonsymmetric and 2 for symmetric
odd = 1 for odd, symmetric filters
fir_nchan = 1 for up and down conversion
The PFIR coefficients are programmed using the cmd5016 configuration software.The cmd5016 program reports
the maximum number of taps available for the configuration. The cmd5016 program uses the mode_ab(cd), splitiq,
cic_dec, fir_dec, fir_diff, fir_nchan, and pfir_coef keywords to program the filters.
If there are multiple filter sets, the number of filters stored in memory will limit the number of coefficients per set . The
filter supports odd or even symmetry. If the user’s filter is significantly shorter than the maximum filter supported, the
clock is stopped to the filter block, saving power.
The filter coefficients are zero-appended to the allowable number of taps. The cmd5016 software in the .ANL
extension file reports the number of taps in the user-specified filter file, the PFIR filter mode, and the number of PFIR
taps in the programmed configuration.
Gain for the FIR is:
Gain = sum (coefficients) x 2^{(fir_shift − 21)}.
The overall_gain pseudo-command is normally used to set the PFIR gain.
There is an application note on DDC gain, and using cmd5016 has examples for specific applications of the PFIR
for DDC usage.
13.8 Power Meter
The PFIR output data is input to the power meter. The power meter integrates the I^2+Q^2 power over a number
of PFIR output samples. The power meter output is read as a 32bit result over the Microprocessor port.
The power meter squares the I or Q top 12 bits of the data, keeps the top 17 bits of the result, and integrates it for
up to 2¹⁶ words. The number of words is I or Q samples. Handshaking is provided to let the user know when data
is ready. Note that the integration is over a number of words so if the data is complex the number of samples integrated
is one half the number of words. If the filters are configured in a splitiq mode then the power meters of the real and
imaginary channels need to be combined by reading both the I and Q channel power meters and adding the results..
A sync is available to start the power measurement period. The power meter automatically starts a new measurement
at the conclusion of the last one. The contents of the power meter registers should be considered unstable from eight
clocks after input sync to eight clocks plus an output sample time. (The actual unstable time is around 0.5 ns, so even
reading during this window provides correct answers most of the time.) Reading during data transfer results in an
erroneous output (some bits being updated, while others are not) but does no other harm.
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