參數(shù)資料
型號(hào)： GC4116
廠商： Electronic Theatre Controls, Inc.
英文描述： MULTI-STANDARD QUAD DUC CHIP
中文描述： 多標(biāo)準(zhǔn)四數(shù)字上芯片
文件頁數(shù)： 11/57頁
文件大?。?/td> 401K
代理商： GC4116
GC4116 MULTI-STANDARD QUAD DUC CHIP
DATA SHEET REV 1.0
19992001
GRAYCHIP,INC.
- 6 -
APRIL 27, 2001
This document contains preliminary information which may be changed at any time without notice
The interpolated signal is modulated by a sine/cosine
sequence generated by the NCO. In the real output mode the
real part (I-half) of the complex result is saved as the channel
output.
In the complex output mode the CIC interpolation is cut
in half and the NCO/mixer calculates both the I-half and
Q-half of the complex result. In this mode the complex output
sample rate is one-half the clock rate, with the I and Q halves
multiplexed together onto the same output bus.
3.3.1 The Programmable Interpolate By 2
Filter
(PFIR)
The input samples are filtered by two stages of
interpolate by 2 filtering before they are interpolated by the
CIC filter. The first stage interpolate by two filter is a 63 tap
filter with programmable 16 bit coefficients. The PFIR will
accept either complex or real input data. If the input samples
are complex, the filter doubles the input rate by inserting
zeroes between each sample, and then low pass filters the
result. If the input samples are real (REAL in address 1 is
set), the filter translates the real samples down by F
IN
/4,
where F
IN
is the input sample rate, by multiplying them by the
complex sequence +1, -j, -1, +j,
…
, and then lowpass filters
the result. This generates a single-sideband modulation of
the real input. Note that in the real input mode the data is
entered as pairs of samples packed into the complex input
word format (see Section 3.2). If double sideband real
upconversion is desired, then the chip should be operated in
the complex mode with the Q-half of each complex pair set
to zero.
The PFIR filter passband must be flat in the region of the
signal of interest, and have the desired out of band rejection
in the region that will contain the interpolation image. Figure
6 illustrates the passband and stopband requirements of the
filter. F
IN
is the input sample rate to the channel. 2F
IN
is the
output sample rate of the PFIR. A common use of the PFIR
is to pulse shape digital data. The PFIR will accept QPSK,
O-QPSK, PSK, PAM, OOK,
π
/4-QPSK, or QAM symbols
and then filter them by the desired pulse shaping filter, which
is commonlt a root-raised-cosine (RRC) filter. The symbols
can be entered directly into the chip at the desired symbol
(baud) rate. The application notes in Section 7 describes
sample filter coefficients sets for common standards
(DAMPS, GSM, IS95, UMTS).
Each channel has its own PFIR coefficient memory, so
the same filter, or a different filter, can be used in each
channel.
The user downloaded filter coefficients are 16 bit 2’s
complement numbers. Unity gain will be achieved through
the filter if the sum of the 63 coefficients is equal to 65536. If
the sum is not 65536, then PFIR will introduce a gain equal
to:
, where PFIR_SUM is the sum of
the 63 coefficients.
The 63 coefficients are identified as coefficients h
0
through h
62
, where h
31
is the center tap. The coefficients are
assumed to be symmetric, so only the first 32 coefficients (h
0
through h
31
) are loaded into the chip. A non-symmetric mode
(NO_SYM_PFIR in address 26) allows the user to download
a 32 tap non-symmetric filter as taps h
0
through h
31
. The
newest sample is multiplied by h31 and the oldest is
multiplied by h
01
.
3.3.2 The Compensating Interpolate by 2
Filter (CFIR)
The second stage filter is a fixed coefficient 31 tap
interpolate by 2 filter. The second stage filter always
interpolates by a factor of two. The second filter has a
passband which is flat (0.01 dB ripple) out to 0.6F
IN
and
provides over 90dB of image rejection beyond 1.4F
IN
. The
second filter also compensates for the droop associated with
the CIC interpolation filter described in the next section. The
16 unique coefficients of the symmetric filter are:
-34, -171, -166, 403, 837, -317, -1983, -790,
2820, 3328, -1667, -6589, -4024, 7232, 20602,
26577
The passband of this filter is wide enough to upconvert
digital symbol data with excess bandwidths up to 0.35.
The CFIR output is scaled to have unity gain.
The output rate of the CFIR filter is 4F
IN
in the complex
input mode and is 2F
IN
in the real input mode. The CFIR
output rate relative to the clock rate is F
CK
/N
F
IN
Frequency
0
-100 dB
0 dB
Signal of Interest Passband
(Typically 0.25 to 0.4 of F
IN
)
F
IN
/2
Image Reject Stopband
(Typically starts between
0.6 and 0.75 F
IN
)
Narrow transition band
Power
Figure 6. Typical PFIR Specifications
PFIR_GAIN
PF65536
=
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