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www.fairchildsemi.com
Features
Integrated IF Down Converter
IF bandwidth from 30 MHz to 80 MHz
Operating range between 8.5V to 13.2V
63dB peak conversion gain from IF to baseband
40dB minimum AGC range
Simple interface to SAW filter and A/D converter
Gain control minimizes noise figure and distortion
Tuner control feature interfaces with variety of tuners
Industry standard 24 Lead SSOP package
Applications
Digital Set-top Receivers
Cable Modems
Description
The RC6508 simplifies the front-end design of cable modem
and set-top receivers. It is a cost-effective solution, since it
integrates IF amplifier, AGC, mixer, amplifier, tuner AGC,
VCO, XTAL OSC, and bandgap reference on a single chip.
The RC6508 downconverts the IF signal to baseband signal
for cable modem and set top receivers. The baseband signal
can be digitized and decoded with an external A/D converter
and a custom DSP demodulator. The input can directly inter-
face to a SAW filter and maintain a low noise figure. The gain
can be controlled over a 40dB range through an external
analog input signal. The gain reduction is done in two stages
with minimum noise figure and signal distortion. The IF out-
put is then down converted and filtered using a double bal-
anced mixer. The output can be further filtered with an
external filter prior to A/D conversion. The RC6508 has an
added feature that it provides an optimum tuner AGC control
voltage which is used to control the front end tuner gain.
The IF and Mixer section works at 9V and the oscillator
works on 5V supply. The RC6508 is available in a 24 Lead
SSOP package.
Block Diagram
65-6508-01
VCC_HF
BB_GND
VCC_RF (5V)
R
V
V
V
X
O
X
S
V
V
VCC_BB
BB_Out
HFGND
IF_IN+
17dB
45dB
VCO
x 2
–
+
RF
BB
LO
IF_IN–
IF_AGC
T_Strt
T_AGC
XTAL Osc
BANDGAP
REF
G
RC6508
QAM IF Downc onverter
Rev. 1.1.1