Time constant automatic adjustment circuit for a filter circuit

• US 4,818,903 A
• Filed: 07/17/1987
• Issued: 04/04/1989
• Est. Priority Date: 07/18/1986
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Kawano, Mitsumo
• Primary Examiner(s): Laroche, Eugene R.
• Assistant Examiner(s): Mottola, Steven J.
• Application Number:
  US07/074,723
• Time in Patent Office: 627 Days
• Field of Search: 307/355, 307/521, 307/526, 328/133, 328/134, 328/167
• US Class Current: 327/553
• CPC Class Codes: H03J 7/02 Automatic frequency control H03J7/18 takes precedence
• CPC Class Codes: H03L 7/0805 the loop being adapted to provide an additional control signal for use outside the loop
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop

Abstract

An automatic adjustment circuit for adjusting the time constant of a filter circuit. The adjustment circuit includes a source of reference frequency signal, an oscillator for generating an oscillation signal, and a detector for detecting the difference in one of phase and frequency between the reference frequency signal and the oscillation signal and generating a control signal for automatically adjusting the time constant of the filter circuit.

Claims

1. An automatic adjustment circuit for adjusting a filter circuit, the filter circuit having a time constant, the adjustment circuit adjusting the time constant and receiving a reference frequency signal, said adjustment circuit comprising:

oscillation means for generating an oscillation signal, said oscillation means including a time constant variable filter and a feedback amplifier connected to said variable filter for positive feedback; and

means for detecting a difference in phase between said reference frequency signal and said oscillation signal and generating a control signal for automatically adjusting the time constant of the filter circuit.

2. The adjustment circuit of claim 1 wherein the detecting means includes a phase detector and a frequency detector and means for supplying the control signal both to the filter circuit and the time constant variable filter.

3. The adjustment circuit of claim 1 wherein the filter circuit includes a main filter and the time constant variable filter has the same configuration as the main filter.

4. The adjustment circuit of claim 2 wherein the detecting means includes a frequency divider.

5. A method for adjusting a time constant of a filter circuit comprising the steps of:

generating an oscillation signal using a combination of a variable filter and an amplifier connected to provide positive feedback to said filter;

comparing the phase of said oscillation signal with the phase of a reference frequency signal;

generating a control signal in response to a difference in phase between said oscillation signal and said reference frequency signal; and

adjusting said time constant of said filter circuit with said control signal.

6. The method of claim 5 also including the step of adjusting the time constant of the variable filter with the control signal.

7. An automatic adjustment circuit for adjusting a filter circuit, the filter circuit having a time constant, the adjustment circuit adjusting the time constant and receiving a reference frequency signal, said adjustment circuit comprising:

oscillation means for generating an oscillation signal, said oscillation means including a time constant and variable filter, a feedback amplifier connected to said variable filter for positive feedback; and

means for detecting a difference in frequency between said reference frequency signal and said oscillation signal and generating a control signal for automatically adjusting the time constant of said filter circuit.

8. A method for adjusting a time constant of the filter circuit comprising the steps of:

generating an oscillation signal using a combination of a variable filter and an amplifier connected to provide positive feedback to said filter;

comparing the frequency of said oscillation signal with the frequency of a reference frequency signal;

generating a control signal in response to a difference in frequency between said oscillation signal and said reference frequency signal; and

adjusting said time constant of said filter circuit with said control signal.

9. The method of claim 8 also including the step of adjusting the time constant of the variable filter with the control signal.