| 摘要 |
PURPOSE:To eliminate enough a pulsative noise generated in a phase comparator, and a noise generated in a loop, and also to obtain a PLL circuit whose modulation characteristic is flat and excellent, by inserting and connecting a phase equalizer for correcting a phase characteristic of a low-pass filter, between the low-pass filter and a voltage controlled type oscillator. CONSTITUTION:Between a low-pass filter 5 and a voltage controlled type oscillator 6, a phase equalizer 10 for correcting a phase characteristic of the low-pass filter 5 is inserted and connected. In a transfer characteristic Es of this phase equalizer 10, an amplitude characteristic is denoted as I (the gain is I against a frequency of a signal), and a phase characteristic is set to a characteristic reverse to the phase characteristic of the low-pass filter 5. In other words, the product Fs.Es of the transfer characteristics of the low-pass filter 5 and the phase equalizer 10 is determined by a transfer characteristic F2, therefore, the phase characteristic becomes flat, and also becomes only a prescribed delay quantity. Accordingly, even in case is a cut-off frequency of the low-pass filter 5 is lowered, and it is brought close to a natural frequency (fn) of a PLL circuit, a modulation characteristic M's becomes flat by an effect of the phase equalizer 10, and an excellent characteristic can be obtained.
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