AFC circuit for producing a ripple-free oscillator control voltage
AssigneeKabushiki Kaisha Toshiba
InventorsMitsumo Kawano, Tadashi Terada
Life of this patent
Estimating the term…
Abstract
An AFC circuit using counters, flip-flops and logic gates produces a first pulse signal only when the phase of a VCO output signal lags the phase of a reference signal, and produces a second pulse signal only when the phase of the VCO output signal leads the phase of the reference signal. The first and second pulse signals control a switch to connect a first or a second constant current source to charge or discharge a filter circuit, to thereby produce a control voltage for the VCO. When the VCO output signal is in phase with the reference signal, the switch remains in a neutral position to hold a constant control voltage on the filter.
Claims20
An automatic frequency control (AFC) circuit comprising:
- input terminal means for receiving a reference pulse signal recurring at predetermined cycles;
- voltage controlled oscillating means for outputting an oscillating output pulse signal;
- frequency demultiplying means for demultiplying a frequency of the oscillating output pulse signal, output from said voltage controlled oscillating means, to produce a first pulse signal of the same period as that of said reference pulse signal received at said input terminal means;
- pulse generating means for counting said oscillating output pulse signal from said voltage controlled oscillating means in synchronism with said reference pulse signal, to output thereby a second pulse signal of substantially the same pulse width as that of said first pulse signal, output from said frequency demultiplying means;
- first multiplying means for multiplying said first and second pulse signals during a predetermined period in synchronism with said reference pulse signal, to produce thereby a third pulse signal of a pulse width based on a phase difference between said first and second pulse signals, only when said first pulse signal advance in phase with respect to said second pulse signal;
- second multiplying means for multiplying said first and second pulse signals during said predetermined period in synchronism with said reference pulse signal, to produce thereby a fourth pulse signal of a pulse width based on a phase difference between said first and second pulse signals, only when said first pulse signal lags in phase with respect to said second pulse signal;
- and
- frequency control means for generating a control voltage based on the pulse width of either of said third and fourth pulses, and supplying said control voltage to said voltage controlled oscillating means, to control thereby an oscillating frequency of said voltage controlled oscillating means so as to phase lock said oscillating output pulse signal with said reference pulse signal.
Dependencies are inferred from the claim text.