Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support GroupPage 34
Figure 33 : Spectrum of the Base Band Signal
Each signal path from IC201, pin 6 will now explained in more detail below.
Audio IF processing
C304, being of a very small capacitance, will only pass relatively high frequencies which will effectively
remove any signals below about 5MHz. This coupled with the filtering network of C334, L302, C355 and
R309 ( effectively a high pass filter ) will ensure that only the audio FM carrier at 6MHz and the NICAM
carrier at 6.522MHz pass into the base of Q301. Q301 amplifies the resultant audio IF and this signal is
then coupled via C310 into the audio processor, IC305, at pin 58 ( ANA INI+ ). C336 ensures that no IF
signal passes onto the supply.
IC305 contains further IF amplification and the decoder stages to recover both the mono FM and stereo
NICAM signals. Switching is carried out automatically within the IC. The receiver will automatically default
to the stereo ( NICAM ) signal, but this can be over ridden by the end user by the use of a menu option.
Note that when in the stereo mode, SRS and Dolby can be used, but in the mono mode only stereo wide
is available.
For details on the audio switching circuits, please refer to the Audio Processing section of these notes.
Video IF and signal processing
All the video IF circuitry is contained within IC201, the output on pin 6 ( VIDEO OUT ) is a base band
signal as shown in the above diagram.
From the emitter of Q202, the base band signal is passed through CF202 and L203. These components
effectively comprise a 6MHz trap and will remove any signals in the audio IF range ( FM and NICAM
sound carriers ), thus the signal entering the base of Q203 will be the video signal. R220/R217 and R221
ensure that correct impedance matching is provided to CF202.
Q202 is an emitter follower which gives the correct impedance match and drive signal back to the video
processing circuits contained within IC201. C281 ensures that no video signal appears on the supply line.
From pin 13 ( CVB IN ) of IC201, the video signal is decoded and passes out of the IC as an RGB signal
to drive the CRT via IC901.