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在相位锁定环路中,若要求环路输出频率随预置信道的变化在较大范围内变化时,仅仅依赖环路中的鉴相器输出电压的变化,来控制环路达到锁定,显然是不可能的。因在更换信道时,若电压控制振荡器频率变化比较小,则相应于电压控制振荡器频率变化,鉴相器有一输出电压反馈到电压控制振荡器的电调元件上,促使环路处于新的锁定状态,此仍是一般所谓的细调。但当更换信道时,电压控制振荡器的频率变化范围很大,超出细调所能控制地范
In the phase locked loop, if the loop output frequency is required to vary within a wide range with the change of the preset channel, the loop is controlled to achieve the lock by relying solely on the change of the output voltage of the phase detector in the loop. Apparently, impossible. When the channel is changed, if the frequency of the voltage-controlled oscillator changes relatively small, the phase detector has an output voltage which is fed back to the voltage-controlled oscillator's ESC according to the change of the frequency of the voltage-controlled oscillator, forcing the loop to be in a new Locked state, this is still the general so-called fine-tuning. But when changing the channel, the frequency of the voltage controlled oscillator varies a great range, beyond the fine ground that can be controlled