Automatic frequency control for FM-receiver

• US 4,092,602 A
• Filed: 06/01/1976
• Issued: 05/30/1978
• Est. Priority Date: 06/02/1975
• Status: Expired due to Term

• Current Assignee: ONKYO KABUSHIKI KAISHA
• Original Assignee: ONKYO KABUSHIKI KAISHA
• Inventors: Nishioka, Yuji, Takei, Toshiyuki, Tokyama, Tetsuya
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Ng, Jin F.
• Application Number:
  US05/691,868
• Time in Patent Office: 728 Days
• Field of Search: 325/419-423, 325/346, 325/349, 331/14, 179/15 BT
• US Class Current: 381/3
• CPC Class Codes: H03J 7/02 Automatic frequency control H03J7/18 takes precedence
• CPC Class Codes: H03J 7/08 using varactors, i.e. voltage variable reactive diodes H03J7/06 takes precedence
• CPC Class Codes: H04H 40/45 for FM stereophonic broadcast systems receiving

Abstract

An apparatus for comparing frequency of an object signal with a given reference frequency, with a reference signal generator for developing a reference signal having the reference frequency. If the object signal is frequency-modulated, then its center frequency is compared with the reference frequency. A switching signal generator, switching circuitry actuated by the switching signal, a frequency discriminator, low-pass filters and a voltage comparator are also provided. Actuated by the switching signal, the discriminator alternately discriminates the frequencies of the object and reference signals, and the averaged discrimination output voltages are compared by the comparator to give the indication of comparison of the frequencies of the object and reference signals.

Claims

1. An automatic frequency control device for an FM-receiver of the type having a frequency convertor, an intermediate frequency amplifier and a frequency demodulator, and in which the frequency convertor is provided with a local oscillator to convert an incoming carrier into an intermediate frequency signal, said automatic frequency control device comprising:

means for developing a reference signal having a predetermined intermediate frequency (f_o);

means for developing a switching signal of 50% duty cycle;

a frequency discriminator;

means for connecting said discriminator alternately to said reference signal and to said intermediate frequency signal obtained from said intermediate frequency amplifier synchronously with said switching signal;

means for switching the output of said discriminator synchronously with said switching signal to obtain separate discrimination outputs of the reference signal and the intermediate frequency signal respectively;

means for deriving, from the discrimination outputs, average discrimination output voltages (E_D, E_R) of the reference signal and the intermediate frequency signal, respectively;

subtractor means connected to said discriminator outputs for obtaining the voltage difference (E_D - E_R) therebetween;

automatic frequency control means connected to be controlled by said difference voltage for regulating the frequency of said local oscillator;

a phase-lock-loop type stereo multiplex reproduction circuit which includes;

an amplifier connected to the output of said frequency demodulator;

an oscillator to transmit a frequency or phase change signal according to regulation voltage;

frequency divider means to divide an output signal from said oscillator;

a phase comparator to compare the phase of an output signal from said frequency divider means and the phase of the stereo pilot signal in the composite signal transmitted from said amplifier, an output from said phase comparator being connected to said oscillator to regulate the frequency or phase thereof; and

a synchronous detector to reproduce two audio signals separated from the composite signal by the output signal from said frequency divider means, the output signal from said frequency divider means being further used as said switching signal.