PLL circuit and TV receiver using it, and improvement in beat of TV receiver

Abstract

A PLL circuit is used for a super-heterodyne television receiver. In the PLL circuit, a reference signal oscillator circuit generates a reference signal, and the reference signal is compared to a LO signal in a phase comparator. The phase comparator includes an oscillating circuit, a series circuit of a correcting capacitor and an oscillator corresponding to a predetermined IF signal frequency, another correcting capacitor, and a switch. The switch is turned ON or OFF only when receiving a particular channel in which interference occurs, so as to shift the frequency of the reference signal by several ten kHz. This reduces beats in a particular channel, and prevents deterioration of picture quality in other channels. That is, interference in a particular channel can be reduced without causing any adverse effects in other channels having a relatively high frequency.

Description

technical field

[0001] The present invention relates to a PLL circuit suitable for superheterodyne receivers such as television receivers, a television receiver equipped with the circuit, and a beat improvement method of the television receiver. Background technique

[0002] Figure 5 It is a block diagram showing the electrical configuration of a television receiver 1 corresponding to the NTSC or PAL broadcasting system using the superheterodyne system. Receive RF (high frequency) signal from antenna 2 input, first only take out required signal component at the input tuning circuit 3 that band-pass filter is formed, then after high-frequency amplifying circuit 4 amplifies, in the stage that band-pass filter forms In the inter-tuning circuit 5, unnecessary signal components are removed. The RF signal is sent to the mixing circuit 6, mixed with the LO (Local Oscillator) signal generated by the Local Oscillator circuit 7, subjected to frequency conversion, and converted into ...

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