GC4016 Datasheet, PDF (63/83 Pages) Texas Instruments – MULTI-STANDARD QUAD DDC CHIP

GC4016 MULTI-STANDARD QUAD DDC CHIP
DATA SHEET REV 1.0
7.6 EXAMPLE PFIR FILTER SETS
The spectral requirements of the PFIR filter are shown in Figure 11 in Section 3.3.6. The filters in Table 26 provide passband
bandwidths which are between 17% and 150% of the down converter channel output sample 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.
Table 26: Default PFIR Filters
Name
Usable
Output
Bandwidth
Passband
Cutoff
Passband
Ripple
(pk to pk)
Stopband
Start
Stopband
Rejection
near/far
PFIR Gain Applications
Taps (first 32)
pfir_17
17%
pfir_34
34%
0.085
0.17
0.01dB 0.125
0.02dB 0.3
97dB/
120dB
83dB/
108dB
3.1262
(204881)
2.2370
(146605)
8x oversampled
outputs.
4x oversampled
outputs,
2X GSM or EDGE
outputs
6 17 33 49 54 33 -28 -132 -263 -380 -424
-329 -49 408 964 1461 1690 1445 597
-826 -2589 -4252 -5228 -4908 -2819 1222
7006 13910 20982 27118 31289 32767
14 30 41 27 -29 -118 -200 -212 -95 150
435 598 475 5 -680 -1256 -1330 -653 669
2112 2880 2269 101 -2996 -5632 -6103
-3091 3666 13042 22747 30053 32767
pfir_68
68%
pfir_80
80%
pfir_100 100%
0.34
0.015dB 0.5
0.4
0.15dB 0.5
0.5
0.2dB 0.6
90dB/
98dB
78dB/
93dB
75dB/
84dB
1.2140
(79563)
1.1494
(75329)
0.9189
(60221)
2x oversampled
outputs, 1X GSM
or EDGE outputs
1.5x oversampled
outputs, Default
filter for most
applications
Single wideband
DDC mode (See
Section 3.4.2)
2 1 -11 -23 -2 45 43 -48 -117 -8 191 155
-189 -375 26 579 358 -601 -918 248 1469
618 -1680 -1995 1104 3690 845 -5354
-5506 6574 24277 32767
31 136 208 107 -123 -181 69 277 46 -353
-235 358 483 -246 -750 -24 967 470 -1046
-1081 884 1817 -360 -2608 -689 3365
2594 -3992 -6527 4407 23277 32767
-30 -141 -180 2 151 -34 -186 87 232 -171
-273 293 292 -458 -270 668 181 -916 4
1192 -325 -1479 837 1758 -1647 -2005
3015 2201 -5914 -2326 19169 32767
pfir_150 150%
0.75
0.75dB 0.82
50dB/
0.6320 Single wideband -32 -234 98 -24 -74 165 -199 138 13 -198
65dB
(41417) DDC mode (See 329 -323 149 145 -437 577 -456 73 445
Section 3.4.2)
-867 955 -576 -213 1138 -1778 1706 -659
-1331 3909 -6474 8360 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 32 taps of the 63 tap filter. The final 31 taps are a mirror image of the first 31 taps. The center taps are scaled to the full
scale positive value of 32767.
The Gain is PFIR_SUM/65536, the value in parenthesis is the PFIR_SUM
The recommended default filter is PFIR_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.
The PFIR can also be used to apply receive filters for digital modulation formats such as QPSK, OQPSK or QAM. The most
common receive filter is the root-raised cosine (RRC) filter. A program (written in C) designed to generate RRC pfir filters is
available from graychip by e-mail or from the web. This program asks for the input sample rate, the baud rate and the desired
roll off (alpha) factor. The output is a 63 tap PFIR filter tap file and a GC4016 command file.
© GRAYCHIP,INC.
- 58 -
August 27, 2001
This document contains information which may be changed at any time without notice