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PRODUCT SPECIFICATION
RC6516
8
P
Applications Discussion
System Overview
The RC6516 is used in a Zenith Digital Cable Modem using
multi-level VSB formats. The RC6516 performs IF amplifi-
cation with gain control, synchronous demodulation of I and
Q channels and carrier recovery using a Frequency and
Phase Lock Loop. The I Channel analog output is digitized
in an A/D converter at a rate of 10.76 MHz. The digital data
is then used by the Digital Logic IC to perform segment sync
recovery, signal polarity correction, symbol clock recovery,
AGC and AFC control, channel equalization, phase error
tracking, data de-interleaving, Reed Solomon error control
and data slicing. (The block diagram of a typical receiver
system using RC6516 is shown in Figure 1.
The RC6516 is between a SAW filter and an A/D. The
RC6516 output is AC coupled to an 8 bit or 10 bit A/D. An
FPLL circuit is used for carrier recovery and synchronous
demodulation. A small pilot signal is present in the received
signal to aid in carrier recovery. A microprocessor is used to
tune the two local oscillators, initialize the system during
start up and monitor system performance.
Figure 2 shows the typical external components and connec-
tions required for the operation of the RC6516.
Figure 1. VSB Receiver Front End
Table 2. Signal Levels and Gain Distribution in Receiver Front-End
V
CC3
= 15V, V
CC1,2
= 12V, T
A
= 0 to 70
°
C unless otherwise specified.
Parameter
Tuner Input
Tuner Gain
SAW Filter Gain (-Loss)
IF Input (Diff-in)
LNA Gain
VGA Gain
Mixer Input (Diff-in)
Mixer Input rms
Mixer Gain
Max. Output (Diff-out)
Filter Amp (Diff-in Sng-out) GAIN
Iout+ Output (rms)
Iout (peak-to-peak)
Max.
Level
-28.9
34
-18
-12.9
25.8
19.6
32.5
42.2
10.9
148
3.6
224
1
High
Level
-21.3
34
-18
-5.3
25.8
12.0
32.5
42.2
10.9
148
3.6
224
1
Mean
Level
-1.3
33.5
-18
14.2
25.8
-7.5
32.5
42.2
10.9
148
3.6
224
1
Low
Level
18.7
21.4
-18
22.1
22.8
-12.4
32.5
42.2
10.9
148
3.6
224
1
Min
Level
23.7
19.1
-18
24.8
20.1
-12.4
32.5
42.2
10.9
148
3.6
224
1
Unit
dBmV
dB
dB
dBmV
dB
dB
dBmV
mVrms
dB
mVrms
dB
mVrms
Vpp
GAIN = 32 dB
SY1LO. 2LO.
TUNER
SAW
FILTER
LOSS = 20 dB
41-47 MHz
DIGITAL
LOGIC
A/D
8 BITS
1175A
8
DATA
RC6516
IF AMPLIFIER
DEMODULATOR
AGC CONTROL 2
START UP
MICRO PROCESSOR
RF
SIGNAL
DELAYED
AGC
BUS
AFC DFT
BUS
65-7564