AUTOMATIC FREQUENCY CONTROL CIRCUIT

• US 3,764,917 A
• Filed: 06/29/1972
• Issued: 10/09/1973
• Est. Priority Date: 09/15/1969
• Status: Expired due to Term

• Current Assignee: North American Philips Consumer Electronics Corp (Koninklijke Philips N.V.)
• Original Assignee: Dong Woo Rhee
• Inventors: Rhee, Dong Woo
• Primary Examiner(s): Mayer, Albert J.
• Application Number:
  US05/267,625
• Time in Patent Office: 467 Days
• Field of Search: 325/416-423,346-348 329/136,178,179,122 331/176,182,183 307/237 178/DIG.26
• US Class Current: 455/208
• CPC Class Codes: H03J 7/10 Modification of automatic frequency control sensitivity or linearising automatic frequency control operation

Abstract

Automatic frequency control (AFC) circuitry includes a signal mixing means for deriving a difference signal from intercepted and locally developed signals, detecting means responsive to said difference signal to provide an output error signal, and a limiting means restricting the output error signal feed back to a locally developed signal means whereby the pull-in and hold-in ranges of the AFC system are controlled by the limiting means and manual switching to enhance station selection is rendered unnecessary.

Claims

1. Automatic frequency control (AFC) circuitry comprising:

signal receiving means;

local signal generating source in the form of an oscillator;

signal mixing means coupled to said signal receiving means and said local signal generating source for deriving a frequency difference signal;

amplifier means coupled to said signal mixing means and tuned to a given frequency;

detector means coupled to said amplifier means and providing an output signal in response to deviations of the frequency of an applied signal from the tuned frequency of said amplifier means;

filtering means coupled to said detector means and responsive to said deviation in signal frequency for providing an error signal in the form of a DC potential; and

limiting means including a pair of complimentary transistors parallel coupled to a potential reference level and to said filtering means and said local signal generating source, said limiting means DC coupling said filtering means to said local signal generating source said limiting means automatically responding to a given maximum magnitude of said error signal to render a substantial reduction in said AFC potential below said given maximum magnitude when the input to said limiting means exceeds said maximum magnitude whereby error correction to a nearby channel is prevented.

2. The AFC circuitry of claim 1 wherein said signal receiving means is responsive to frequency modulated (FM) signals.

3. The AFC circuitry of claim 1 wherein said limiting means includes an impedance DC coupling said filtering means to said local signal generating source.

4. The AFC circuitry of claim 1 wherein said limiting means includes a pair of complimentary transistors having emitter electrodes parallel coupled to a potential reference level, base electrodes parallel coupled to said filtering means, and collector electrodes parallel coupled to said local signal generating source and said filtering means.

5. The AFC circuitry of claim 3 wherein said impedance is in the form of a resistor.