Service Manual
9.2.1 Front-end Circuit
87
via TV level, to
. In the mixer, the wanted signal and the first LO signal are mixed to
sor U501 for further processing.
The HF signal from the low-pass filter passes through the electrically tunable band-pass filter controlled
via TV level, to remove out-of-band interference signal and to send wanted band-pass signal to the
low-noise amplifier (U402). The amplified signal goes to a band-pass filter controlled
remove out-of-band interference signal generated during amplification, and to send wanted HF signal to
the mixer.
The wanted signal passes through the RF band-pass filter and low-noise amplifier and goes to the mixer
(U403). Meanwhile, the first local oscillator (LO) signal generated by VCO passes through the low-pass
filter and also goes to the mixer
generate the first IF signal (73.35MHz). Then the signal passes through the LC to suppress carrier other
than the first IF signal, and to increase the isolation between the mixer and the IF filter. After that, the first
IF signal goes to crystal filter (Z401) for filtering, and is sent to the two-stage IF amplifier circuit for
amplification. Then the amplified signal goes to the IF proces
9.2.2 Rear-end Circuit
16.8MHZ
Reference
frequency
IF input
SSI TO OMAP
Figure 9-3 Diagram of IF Processor
The first IF signal (73.35MHz) output by the IF amplifier goes into U501 via Pin 47, where the signal is
d to the second IF signal (2.25MHz). Then the signal is converted to digital signal via ADC
d output via the SSI interface. Finally, the digital signal is sent to DSP (OMAP5912) for
ation.
ys reference frequency of 19.2MHz and shares the crystal with OMAP. The second LO VCO
comprises an oscillator, a varactor and some other components, to provide the 71.1/75.6MHz LO signal.
converte
sampling, an
demodul
U501 emplo
To Next Page
Loading...
