Oscillating circuit for producing an output signal synchronous with an input signal

• US 6,498,536 B1
• Filed: 05/11/2000
• Issued: 12/24/2002
• Est. Priority Date: 05/13/1999
• Status: Expired due to Fees

• Current Assignee: NEC Electronics Corporation (Renesas Electronics Corporation)
• Original Assignee: NEC Corporation
• Inventors: Mori, Kenji
• Primary Examiner(s): Mis, David C.
• Application Number:
  US09/568,677
• Time in Patent Office: 957 Days
• Field of Search: 331/1.A, 331/10, 331/11, 331/14, 331/17, 331/18, 331/25, 331/DIG.2, 327/156-159, 455/260, 375/376
• US Class Current: 331/11
• CPC Class Codes: H03L 2207/06 Phase locked loops with a controlled oscillator having at least two frequency control terminals
• CPC Class Codes: H03L 7/087 using at least two phase detectors or a frequency and phase detector in the loop
• CPC Class Codes: H03L 7/095 using a lock detector H03L7/087 takes precedence
• CPC Class Codes: H03L 7/113 using frequency discriminator
• CPC Class Codes: Y10S 331/02 Phase locked loop having lock indicating or detecting means

Abstract

An oscillating circuit removes a phase difference from between an input signal variable in frequency and a free-running oscillation signal through a two-step voltage-to-frequency control, wherein a frequency comparator, a detector, a flip flop circuit cooperates with a counter so as to vary a control range of the voltage-controlled oscillator in the vicinity of the input frequency, and, thereafter, a phase comparator makes the free-running oscillation signal synchronous with the input signal through the phase comparison therebetween, even if the voltage-to-frequency characteristics of the voltage-controlled oscillator is deviated from a design range, the deviation is taken up through the first-step control so that the manufacturer can delete an external regulator from the oscillating circuit.

Claims

1. An oscillating circuit for producing an output signal synchronous with an input signal, comprising:

a signal input node effective to receive said input signal;

a voltage-controlled oscillator including a feedback loop having voltage-to-frequency characteristics achieved in a certain control range, and responsive to a control voltage signal effective to change a frequency of said output signal;

a control loop connected to said signal input node and said voltage-controlled oscillator so as to compare said frequency of said output signal with a frequency of said input signal to see whether the difference between said input and output signals falls within said certain control range, and changing a first sub-signal of said control voltage signal so as to make said frequency of said output signal substantially coincident with said frequency of said input signal when said difference is out of said certain control range; and

said feedback loop is connected to said signal input node and said voltage-controlled oscillator, and controls said voltage-controlled oscillator with a second sub-signal of said control voltage signal so as to make said output signal and said input signal in-phase when said difference is within said certain control range.

2. The oscillating circuit as set forth in claim 1, wherein said control loop includes:

a frequency comparator comparing said frequency of said output signal with said frequency of said input signal to see whether said difference between said input signal and said output signal falls within said certain control range so as to produce a first control signal representative of the result of comparison, and

a first control signal generator connected between said frequency comparator and said voltage-controlled oscillator and responsive to said first control signal so as to vary said first sub-signal.

3. The oscillating circuit as set forth in claim 1, wherein said feedback loop includes a phase comparator connected to said voltage-controlled oscillator so as to produce said second sub-signal.

4. The oscillating circuit as set forth in claim 2, wherein said control signal generator includes:

a counter changing a count stored therein on the basis of a pulse train produced from said input signal while said first control signal is representing that said input signal is out of said certain control range, and

a converter connected between said counter and said voltage-controlled oscillator and changing said first sub-signal to a magnitude corresponding to said count.

5. The oscillating circuit as set forth in claim 4, wherein said control loop further includes a frequency divider connected to said counter for producing said pulse train from said input signal.

6. The oscillating circuit as set forth in claim 5, wherein said first control signal generator further includes:

a second control signal generator connected between said frequency comparator and said counter and responsive to said first control signal so as to produce a second control signal of a first level representative of a count-down operation when said frequency comparator finds that said output signal and said input signal are out of phase,

said second control signal generator changing said second control signal to a second level representative of a count-up operation when said count reaches a threshold value through said count-down operation.

7. The oscillator as set forth in claim 6, wherein said second control signal generator includes:

a detector connected to said frequency comparator and responsive to said first control signal for producing a third control signal representative of one of locked state and unlocked state, and

a flip-flop circuit connected between said detector, a source of said second level and said counter and responsive to said third control signal so as to change said second control signal between said first level and said second level.

8. The oscillating circuit as set forth in claim 7, wherein said detector is activated after a delay time from the production of said first control signal representative of said difference being out of said certain control range.

9. The oscillating circuit as set forth in claim 6, wherein said frequency comparator is deactivated while said second control signal is representing said count-down operation.

10. The oscillating circuit as set forth in claim 6, wherein said control loop further includes:

a first switching circuit connected between said frequency divider and said counter and transferring said pulse train to said counter while said first control signal is representing said input signal out of said certain control range, and

a second switching circuit connected between said signal input node and said feedback loop and transferring said input signal to said second switching circuit while said first control signal is representing said input signal falls within said certain control range.

11. The oscillating circuit as set forth in claim 10, wherein said control loop further includes a third switching circuit having input nodes respectively connected to said signal input node and said voltage-controlled oscillator and an output node connected to said frequency divider and responsive to said second control signal representative of said count-up operation so as to transfer said input signal to said frequency divider, said third switching circuit being further responsive to said second control signal representative of said count-down operation so as to transfer said output signal to said frequency divider.

12. An oscillating circuit for producing an output signal substantially synchronous with an input signal, said oscillating circuit comprising:

a signal input node effective to receive said input signal;

a voltage-controlled oscillator including a feedback loop having a voltage-to-frequency characteristic effective within a control range, said voltage-controlled oscillator being effective to receive a control voltage signal and output said output signal in response to said control voltage signal;

a control loop connected to said signal input node and said voltage-controlled oscillator, said first control loop including a comparator which compares said frequency of said output signal with a frequency of said input signal and determines a difference therebetween, said first control loop alters said control voltage signal so as to alter said output signal and thereby make said difference fall within said certain control range when said difference is out of said certain control range; and

said feedback loop is connected to said signal input node and said voltage-controlled oscillator, said feedback loop controls said voltage-controlled oscillator with a second sub-signal of said control voltage signal so as to make said output signal and said input signal in-phase.