參數(shù)資料
型號： GC4116
廠商： Electronic Theatre Controls, Inc.
英文描述： MULTI-STANDARD QUAD DUC CHIP
中文描述： 多標(biāo)準四數(shù)字上芯片
文件頁數(shù)： 13/57頁
文件大?。?/td> 401K
代理商： GC4116
GC4116 MULTI-STANDARD QUAD DUC CHIP
DATA SHEET REV 1.0
19992001
GRAYCHIP,INC.
- 8 -
APRIL 27, 2001
This document contains preliminary information which may be changed at any time without notice
32 BITS
20 BITS
32 BITS
FREQUENCY
WORD
SINE/COSINE
OUT
23 MSBs
5 BITS
18 MSBs
DITHER
GENERATOR
PHASE
OFFSET
16 BITS
SINE/COSINE
LOOKUP
TABLE
Figure 8. NCO Circuit
3.3.6 The Numerically Controlled Oscillator
(NCO)
The tuning frequency of each down converter is
specified as a 32 bit word and the phase offset is specified
as a 16 bit word. The NCOs can be synchronized with NCOs
on other chips. This allows multiple down converter outputs
to be coherently combined, each with a unique phase and
amplitude. A block diagram of the NCO circuit is shown in
Figure 8.
The tuning frequency is set to FREQ according to the
formula FREQ = 2
32
F/F
CK
, where F is the desired tuning
frequency and F
CK
is the chip’s clock rate. The 16 bit phase
offset setting is PHASE = 2
16
P/2
π
, where P is the desired
phase in radians ranging between 0 and 2
π
. Note that a
positive tuning frequency should be used to upconvert the
signal. A negative tuning frequency can be used to spectrally
flip the spectrum of the desired signal. FREQ and PHASE
are set in addresses 16 through 31 of the frequency and
phase pages.
The NCO’s frequency, phase and accumulator can be
initialized and synchronized with other channels using the
FREQ_SYNC, PHASE_SYNC, and NCO_SYNC controls in
addresses 8 through 11. The FREQ_SYNC and
PHASE_SYNC controls determine when new frequency and
phase settings become active. Normally these are set to
“always” so that they take effect immediately, but can be
used to synchronize frequency hopping or beam forming
systems. The NCO_SYNC control is usually set to never, but
can be used to synchronize the LOs of multiple channels.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-150
-100
-50
0
G
dlo.nodither.894784853.ppow
No dither
-105 dB
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-150
-100
-50
0
Frequency (Fs)
G
dlo.dither.894784853.ppow
Ftune = 5/24 Fs
-116.4 dB
-116 dB
a) Worst case spectrum without dither
b) Spectrum with dither (tuned to same frequency)
FREQ=5/24 F
S
FREQ=5/24 F
S
Figure 9. Example NCO Spurs
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-150
-100
-50
0
G
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-150
-100
-50
0
G
-121 dB
-107 dB
a) Plot without dither or phase initialization
b) Plot with dither and phase initialization
Figure 10. NCO Peak Spur Plot
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