“增你智”(Zenith)电视机的特点是具有键盘接触指令电调谐系统。它是一个微处理机控制的频率合成器,而这个频率合成器用一个锁相环路精确地控制调谐器的本机振荡部分。与开环线路相比,闭环系统不需要由电视观众人工调谐,且不存在振荡频率的漂移问题。下图所示为该系统的方框图。微处理机从键盘或遥控装置接受输入指令,这个输入 The “Zenith” TV features a keyboard-command electrical tuning system. It is a microprocessor-controlled frequency synthesizer, which uses a phase-locked loop to precisely control the tuner’s local oscillator. Closed-loop systems do not need to be manually tuned by the television viewer compared to open-loop circuits, and there is no drift in the oscillation frequency. The figure below shows the system block diagram. The microprocessor accepts input commands from the keyboard or remote control, this input