Frequency synthesizer tv tuner2
A frequency synthesizer TV tuner is a closed loop system, self-compensating for varactor tolerances and component drifts. The following section explains the Frequency synthesizer TV tuner in details.
Overview of the Frequency Synthesizer:
- Frequency synthesizer TV tuner provides easy interface with digital displays and simplifies remote control design.
- It is highly reliable and has no alignment problems.
- The block diagram of Fig. 1.1 illustrates the frequency synthesizer system for electronic channel selection.
- The dotted chain block represents a standard VHF or UHF varactor tuner.
- The output of the local voltage controlled oscillator (VCO) is amplified to an acceptable level for driving a digital emitter coupled logic (ECL) prescaler (divider).
- The purpose of the prescaler is to divide down the local oscillator high frequencies to a range that can be processed and counted by standard TTL logic.
- The output of the prescaler is fed to the programmable divider which is the heart of the system.
- Its output is passed on to a frequency and phase comparator where it is compared with a crystal controlled reference frequency.
- Then the comparator output is fed to an integrator-amplifier, which in turn provides voltage control to the varactor tuner input.
Figure 1.1 Block diagram of a frequency synthesizer TV tuner.
- The divide ratio of the programmable counter determines the desired channel.
- At the comparator, there are two significant signals–the counted output and the reference signal.
- When these two signals differ in frequency or phase, a dc error voltage is applied to the tuner VCO with a suitable polarity in order to reduce the frequency and phase error to zero.
- At this time the VCO is at the selected channel frequency.
- A touch tuning type entry system is used for channel selection and a modern seven segment display is employed for channel indication.