Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support Group Page 31
Tuning and IF control is provided by the system microprocessor, IC 101 via the I C bus line. The tuner
2
itself is a digitally controlled device, which eliminates the need for a separate VT line generator circuit.
As the tuner is controlled directly from the microprocessor, it is easier to provide direct channel entry and
as an added feature the set is also equipped with auto channel sorting. This is across the normal UK
channel band and cable channels.
Most of the IF circuitry is contained within IC201 ( Video IF ) and IC305 ( Audio IF ), the minimal amount
of external components provide for IF signal filtering - see IF signals section for more details.
Tuner and IF processing
All IF processing is carried out within either IC201 for video or IC305 for audio. Initially the IF from the
tuner enters IC201 and is decoded to produce the base band signal - see the spectrum diagram shown
later in these notes. As this is a composite of the video and audio IF ( FM and NICAM ) signals it is
necessary to process it further to ensure that no corruption occurs in the later stages. The circuit shown
below serves this function.
Figure 31 : Tuner and IF Signal Path
When the user selects an off air signal, data is taken from the NVM and used by the microprocessor to
generates the data signal fed into the tuner. This data will control the digital to analogue converter
contained within the tuner module so that the correct voltage is applied to the varicap diodes. Like most
tuners it is necessary to provide a 32 volt supply line to allow for total band coverage of the tuning voltage,