Service Manual
electrically tunable band-pass filter to get useful signals. After passing through the RF band-pass filter
and LNA (Q6102), the RF signals together with the first LO signal feed to the mixer for the first frequency
conversion, to generate the first IF signal (73.35MHz). The mixer that employs the passive diode can
ensure good dynamic range and port isolation. The LO signal (3-5dBm) from the VCO feeds to Q6103
to get a gain (17dB). The first LO signals (73.35MHz) pass through the crystal filter (Z6100) to remove
out-of-band spurious signals, and then feed to the two-stage IF amplifier circuit (composed of Q6133 and
Q6134) for amplification. Finally the amplified signals go to the IF IC for processing
11.2.2 Receiver Back-end
Figure 11-3 Diagram of IF Processor
The first IF signal (73.35MHz) output by the IF amplifier goes into IF IC via Pin 47, where the signal is
converted to the second IF signal (2.25MHz). Then the un-demodulated digital I/Q signal output from the
SSI interface is sent to U302 for demodulation. IF IC employs a reference frequency of 19.2MHz and
shares the crystal with U302. The second LO VCO consists of the external transistor, varactor and some
other components, to provide the second LO signal. The 18MHz clock frequency is generated by the LC
resonance loop (D702, L715 and C745).
DSP (U302) gets the audio signal from IF IC (U701). Then this signal goes through U302 to output data
signal, which is sent to U231 and PIN44 (SSI_DI) for digital-to-analog conversion. Finally, the output
analog audio signal will be subjected to gain control, and then fed to the speaker.
11.3 Frequency Generation Unit (FGU)
11.3.1 PLL Synthesizer
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