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PRODUCT SPECIFICATION
RC6564A
7
Typical Performance Characteristics
(Continued)
Figure 3. SFDR vs RC6564A
(Fairchild Semiconductor Demo Board
with 64 QAM demodulator)
S/N vs. IF Input Power RC6564
(Fairchild Semiconductor Demo Board
with 64 QAM demodulator)
SFDR Comparison for RC6564A & RC6508/1175A
10
15
20
25
30
35
40
45
50
55
60
20
25
30
35
40
IF Gain, dB
45
50
55
60
65
S
Comparison of 64 QAM Front End Solutions
10
15
20
25
30
35
40
-60
-50
-40
IF Input Power, dBm
-30
-20
-10
0
S
Applications
The RC6564A is specially suited for use in set-top boxes and
cable modems for decoding QAM modulated signals based
on IF sampling techniques. The RC6564A simplifies the
front-end design and makes it more cost effective by integrat-
ing in a single chip the IF-to-Digital functionality. The other
major components required for the front-end of the modem
are the tuner, a SAW filter and the appropriate DSP demodu-
lator/decoder.
Modem Applications
Figure 4 below shows the application of RC6564A in IF
bandpass sampling decoding for cable access. The on-chip
VCO provides low-phase noise characteristics. The VCO can
be pulled by the voltage control on VCO_CNTRL. The sam-
pling clock for the A/D conversion can be derived from the
master clock through external frequency synthesis. The full
scale reference signal for A/D is conveniently derived from
the VRT output. The baseband output is referenced such that
the filtered output is automatically in the mid-scale of the A/
D input. The filtered output can be a.c. coupled to the AD_In.
In the application below an external low-pass filter is used to
bandlimit the signals before conversion. The gain is adjusted
by the average voltage on the IF_AGC line to keep the signal
in the optimum range of the A/D input. The T_AGC output is
used to control the tuner gain when the input levels into the
RC6564A are too high.