GC1012B_07 Datasheet, PDF (17/30 Pages) Texas Instruments – 3.3V DIGITAL TUNER CHIP

GC1012B 3.3V DIGITAL TUNER
SLWS138B
3.3 FILTER MODE REGISTER
This register controls filtering, output formatting and the diagnostic input mode.
ADDRESS 5:
Filter Mode Register
BIT
TYPE
NAME
DESCRIPTION
0-2
R/W
DEC[0:2]
The decimation mode. The output sample rate is set using DEC according to the
following table:
F_O
F_O
DECCOMPLEX
REAL
(REAL = 0)
(REAL = 1)
0 or 1F_CK ?
2 F_CK/2 F_CK
3 F_CK/4 F_CK/2
4 F_CK/8 F_CK/4
5 F_CK/16 F_CK/8
6 F_CK/32 F_CK/16
7 F_CK/64 F_CK/32
Where F_CK is the input rate and F_O is the output rate.
3
R/W
-
Unused.
4
R/W
REAL
Output real samples instead of complex samples. The output spectrum is centered from
0 to F_O/2 where F_O is the output rate (see DEC above for the REAL mode). NOTE: The
FLIP bit described below is active low in the real mode.
5
R/W
OFFSET
Offset the complex output spectrum. Used in the complex output mode (REAL=0) to
force the output spectrum to be centered at F_O/2, where F_O is the output sample rate
(see DEC above for the COMPLEX mode). This mode is useful for single-sideband AM
signals because it moves the lower band edge up to zero frequency where it belongs.
The upper half of the spectrum will appear as negative frequencies.
6
R/W
FLIP
Flip the output spectrum. This bit inverts the output spectrum. In the complex mode the
spectrum is flipped about zero. In the real mode the spectrum is flipped about F_O/4,
where F_O is the real mode’s output sample rate. In the complex mode FLIP=1 flips the
spectrum. In the real mode FLIP=0 flips the spectrum.
7
R/W
DIAG
Use the diagnostic ramp for the input to the chip instead of the X input. The ramp counts
from -2048 to +2047 and then starts over again.
The effect on the output spectrum of the REAL, OFFSET and FLIP bits is illustrated in the following
diagram. (F_O is the output sample rate)
-F_O
NORMAL
(FLIP=0
0
OFFSET=0
REAL=0)
+F_O
-F_{O FLIPPED (FLIP=1)} 0
+F_O
-F_O
OFFSET
0
(OFFSET=1)
+F_O
-F_O
OFFSET
AND
0
FLIPPED
(FLIP=1
OFFSET=+1F)^O
-F_O/R2EAL
MODE
0
(REAL=1
FLIP=1)
+F_O/2
-F_O/R2EAL
AND
0
FLIPPED
(FLIP=0
REAL=1)
+F_O/2
Figure 4. Output Spectral Formats
Texas Instruments Incorporated
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