GC4016 Datasheet, PDF (62/83 Pages) Texas Instruments – MULTI-STANDARD QUAD DDC CHIP

GC4016 MULTI-STANDARD QUAD DDC CHIP
DATA SHEET REV 1.0
7.5 EXAMPLE CFIR FILTER SETS
The CFIR filter must be flat over the output passband of interest, and have a stopband which rejects out of band signals
which will fall into the passband of interest. The spectral requirements of this filter are shown in Figure 10 in Section 3.3.5. The
CFIR filter must also compensate for the passband roll off of the CIC filter. The following filters compensate for the CIC roll off
and provide passband bandwidths which are between 17% and 150% of the down converter’s output sample rate (the PFIR
output rate before resampling).
The filter taps can be copied from this table, or requested by e-mail from [e-mail], or downloaded from
the web at www.graychip.com. The filter taps are available in two file formats. The first, <filter_name>.taps, is an ascii listing of
the taps. The second, <filter_name>.cmd, is a command file which could be used to write the filter taps into a GC4016 chip. The
commands are formatted as “write <address> <data_byte>,” where <address> and <data_byte> are unsigned hex integers.
The recommended default filter is cfir_80 which is flat out to 80% of the channel output’s usable bandwidth. The narrower
filters have less ripple and better out of band rejection. The wider filters (100% and 150%) are designed for the single wideband
output per chip mode where all four channels are used as one wideband channel. These modes have more ripple and less out
of band rejection than the narrowband filters.
Table 25: Example CFIR Filters
Name
Usable
Output
Bandwidth
Passband
Cutoff
Passband
Ripple
(pk to pk)
Stopband
Start
Stopband
Rejection
CFIR Gain
(CFIR_SUM)
Applications
Taps (first 11)
cfir_17 17%
cfir_34 34%
cfir_68 68%
cfir_80 80%
(default)
cfir_100 100%
cfir_150 150%
0.085
0.17
0.34
0.4
0.5
0.75
0.01dB 1.5
0.01dB 1.5
0.02dB 1.55
0.025dB 1.5
0.08dB 1.5
0.6dB 1.25
110dB
110dB
100dB
100dB
2.0413
(133781)
1.5429
(101113)
1.2665
(83001)
0.9899
(64877)
100dB
60dB
0.9109
(59695)
0.9154
(59993)
8x oversampled outputs. 5 39 -166 -1301 -3009 -2848
1280 9009 18952 28546 32767
4x oversampled outputs, -24 74 494 548 -977 -3416
2X GSM or EDGE outputs -3672 1525 13074 26547 32767
2x oversampled outputs, 12 -93 -62 804 1283 -1273
1X GSM or EDGE outputs -5197 -3512 8332 24823 32767
1.5x oversampled
outputs, Default filter for
most applications
5 -8 -172 -192 806 1493 -1889
-6182 1085 21109 32767
Single wideband DDC -3 40 -75 -437 291 1951 -489
mode (See Section 3.4.2) -6365 -1185 19736 32767
Single wideband DDC 47 -102 -1184 -1274 1487 3243
mode (See Section 3.4.2) -1798 -7760 15 20939 32767
Key:
The Usable Output Bandwidth is the passband bandwidth expressed as a percentage of the DDC channel output sample rate.
The Passband Cutoff frequency is relative to the DDC channel output sample rate.
The Stopband Start frequency is relative to the DDC channel output sample rate.
The Taps are the first 11 taps of the 21 tap filter. The final 10 taps are a mirror image of the first 10 taps. The center taps are scaled to the full
scale positive value of 32767.
The Gain is CFIR_SUM/65536, the value in parenthesis is the CFIR_SUM
© GRAYCHIP,INC.
- 57 -
August 27, 2001
This document contains information which may be changed at any time without notice