GC4116 Datasheet, PDF (16/57 Pages) List of Unclassifed Manufacturers – MULTI-STANDARD QUAD DUC CHIP

GC4116 MULTI-STANDARD QUAD DUC CHIP
If attenuation is necessary, for example when multiple
channel outputs are to be added together, then the
attenuation should be added as close to the output of the
chip as is possible - preferably only at the end of the sumtree
just prior to going to the D/A.
3.7 FOUR CHANNEL RESAMPLER
The GC4116 contains a resampler which can be used to
feed the up-converter channels in the chip, or can be used as
a general resampling resource for a signal processing
system. The resampler shares the clock to the chip, but its
input, output and control circuitry are independent from the
rest of the chip. The resampler in the GC4116 chip is very
similar to the one in the GC4016 chip.
The resampler requires the use of the Serial Controller
block described in Section 8.
Note that the resampler only works on complex data so
the up converter’s real or split IQ modes, which require two
real samples per complex word, can not use the resampler.
Also, the maximum output sample rate from the resampler is
CK/44 when it is connected to the GC4116’s upconvert
channels. This means the upconvert channels must
interpolate by at least a factor of 44 (N>=11) when using the
resampler.
3.7.1 Resampler Input Format
The resampler inputs are complex samples, 16 bits per
I or Q word. The samples are input to the resampler through
bit-serial input ports, or through memory mapped registers. A
resampler data request signal (RREQ) is output from the chip
to identify when the resampler is ready for another complex
input sample. The request (RREQ) signal may not be
periodic, depending upon the resampling ratio being used.
The bit serial interface to the resampler functions the
same as the serial interface to the channels (see Section 2)
except the resampler does not support real input mode and
the maximum input complex word rate is CK/34.
DATA SHEET REV 1.0
The Serial Controller is used to tell the resampler input
buffer when the next set of serial samples is ready. The
Serial Controller can also be used to generate the serial
clock and frame strobes for the resampler’s input ports (see
Section 3.8).
3.7.2 Functional Description
The resampler consists of an input buffer, an
interpolation filter, and an output buffer. A functional block
diagram of the resampler is shown in Figure 12.
The resampler’s sampling rate change is the ratio
NDELAY/NDEC where NDELAY and NDEC are the
interpolation and decimation factors shown in Figure 12. The
decimation amount NDEC is a mixed integer/fractional
number. When NDEC is an integer, then the exact sampling
instance is computed and there is no phase jitter. If NDEC is
fractional, then the desired sampling instance will not be one
of the possible NDELAY interpolated values. Instead the
nearest interpolated sample is used. This introduces a timing
error (jitter) of no more than 1/(2*NDELAY) times the input
sample period.
The input buffer accepts 16 bit data from the serial input
ports or the memory mapped input registers. The input buffer
serves both as a FIFO between the input and the resampler,
and as a data delay line for the interpolation filter. The 64
complex word input buffer can be configured as four
segments of 16 complex words each to support 4 resampler
channels, or as two segments of 32 complex words each to
support 2 resampler channels, or as a single segment of 64
complex words to support a single resampler channel. The
number of segments is set by NCHAN in address 16 of the
resampler control page.
The interpolation filter zero pads the input data by a
factor of NDELAY and then filters the zero padded data using
a QTAP length filter. The output of the QTAP filter is then
decimated by a factor of NDEC.
Interpolation Filter
Fractional
Decimation
INPUT
BUFFER
NDELAY
QTAP Filter Coefs
NDEC
OUTPUT
BUFFER
Resampling Filter
Figure 12. Resampler Channel Block Diagram
© 1999−2001 GRAYCHIP,INC.
- 11 -
APRIL 27, 2001
This document contains preliminary information which may be changed at any time without notice