ISL5416 Datasheet, PDF (21/71 Pages) Intersil Corporation – Four-Channel Wideband Programmable DownConverter

ISL5416
additional 0 to 3 input samples as programmed by the user.
This additional depth provides for additional programmable
group delay. The additional FIFO depth can only be
programmed at reset. Because the NCOs are enabled after
a depth of 2 is reached, the data into the IHBF/Resampler is
zeroed until the programmed fill depth is reached. If both the
half-band and resampling filters are enabled, the
programmable FIFO depth, together with the NCO2 phase
offset, provides from 0 to 4 FIR2 output sample periods of
programmable group delay in 1/512 increments.
Because the IHBF and RS combination can only interpolate,
for resampling ratios <1, the signal must first be interpolated
to a multiple of the desired sample rate and then decimated
to the final rate. A decimation counter is provided after the
resampling filter to down sample to the desired rate.
The NCO1 and NCO2 frequencies are programmed in IWA =
*011h - *014h. These registers are double buffered. The uP
writes to a holding register. Data is then transferred to the
active registers by a write to IWA = *017h or by a SYNCInX if
enabled in IWA = *000h.
The gain data from the AGC is not interpolated. The output
of the AGC is sampled with each I/Q sample to the output
section.
PHASE OFFSET
0 TO 511/256 SAMPLES
FILL DEPTH BEFORE
ENABLING READS
0, 1, 2, or 3
Fihbf_in
WR
RD
LEAP
COUNTER
DIVIDE
BY
1 OR 2
Fihbf_out
Σ
REG ^{EN N x Fout}
Σ
REG
CO
NCO2
NCO1
0...-15
R
E FIFO
G
DEPTH =
2 + (0 to 3)
SAMPLES
R RR R R
IHBF E E E E ^E
G GG G G
R
E
G
R
E
G
FRACTIONAL
RESAMPLING
INTERPOLATION
R
E
G
FILTER
R
E
G
R
E
G
R
E
G
R
E
G
Fclk
DIVIDE
BY N
Fout
R
E
G
FIGURE 8. IHBF AND RESAMPLER BLOCK DIAGRAM
21