Receiver control for adjusting tuned circuits in HF filter - uses individual computer controlled tuning circuits to produce required adjustment voltage for channel selection

摘要

A receiver oscillator tuning voltage (VTo) produced by a PLL circuit (10) is fed via a series resistor (R1) to a filter capacitor (C) which provides the necessary adjustment voltage (VT) for a tuned circuit. A control micro-processor (16) provides a pulse train, whose mark to space ratio is dependent on channel selection, to the base of an input transistor (T1). The inverted output of the input transistor (T1) is applied to the base of current source transistor (T2) and current sink transistor (T3). Dependent on pulse level (low or high) the collector of either the current source or current sink transistor (T1, T2) will be switched through to increase or decrease the charge potential on the filter capacitor (C) effecting fine control on the tuned circuit adjusting voltage (VT). USE/ADVANTAGE - Accurate tuning process for TV and radio receivers. Uses cheap and cost effective circuitry. Easy to adapt existing TV micro-processor for required tuning pulse outputs.