Phase-locked loop oscillator, and moving-average circuit, and division-ratio equalization circuit suitable for use in the same

• US 5,867,544 A
• Filed: 03/03/1995
• Issued: 02/02/1999
• Est. Priority Date: 03/04/1994
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Taniguchi, Atsuki
• Primary Examiner(s): Ghebretinsae, Temesghen
• Application Number:
  US08/398,570
• Time in Patent Office: 1,432 Days
• Field of Search: 375/376, 375/373, 375/229, 331/2, 331/DIG. 2, 331/1 A, 331/11, 327/147, 327/151
• US Class Current: 375/376
• CPC Class Codes: H03L 7/0992 comprising a counter or a frequency divider

Abstract

In a first phase-locked loop, a digital value corresponding to the mean frequency of an input clock signal is obtained. In a second phase-locked loop, the mean value of the phase difference of an output clock relative to the input clock is measured and is added to the digital value corresponding to the mean frequency, to obtain a control value. From this control value, a control signal for uniformly controlling a dual-modulus frequency divider is generated and supplied to the dual-modulus frequency divider. In a moving-average circuit, a selector selects input data when updating the contents of a serial latch circuit array, and selects an output of the serial latch circuit array when accumulating values. Values serially output from the latch circuit array for accumulation are successively added up using an adder and a latch circuit. In a division-ratio equalization circuit, a calculating circuit calculates quotients a₀, a₁, a₂ . . . a_m when the control value is expressed as 1/(a₀ +1/(a₁ +1/(a₂ + . . . +1/a_m)) . . . ), and the quotients are set as division ratios in programmable frequency dividers connected in cascade, through which a reference clock signal is frequency-divided to obtain the control signal.

Claims

1. A phase-locked loop oscillator comprising:

means for obtaining a first digital value indicating a mean frequency of an input signal;

means for obtaining a second digital value indicating a mean phase difference of an output signal relative to said input signal;

means for calculating a control value on the basis of said first and said second digital values;

means for selecting a division ratio from two division ratios in accordance with a control signal;

a dual-modulus frequency divider for generating said output signal by frequency-dividing a reference signal, said frequency divider being capable of operating with the division ratio selected;

by said selecting means and

frequency divider control signal generating means for generating said control signal for controlling said dual-modulus frequency divider in accordance with said control value.

2. A phase-locked loop oscillator according to claim 1, further comprising synchronization condition judging means for judging whether said output signal is in a synchronized condition or in an out-of-synchronization condition with respect to said input signal, wherein

said control value calculating means calculates said control value based only on said first digital value as long as said synchronization condition judging means judges the condition to be an out-of-synchronization condition.

3. A phase-locked loop oscillator according to claim 2, wherein said control value calculating means determines said control value by using said second digital value rather than said first digital value as long as said synchronization condition judging means judges the condition to be a synchronized condition.

4. A phase-locked loop oscillator according to claim 3, wherein said control value calculating means includes;

a center control value determining means for determining a center control value in such a manner that said center control value progressively approaches said first digital value; and

an adding means for adding a value based on said second digital value to the center control value determined by said center control value determining means.

5. A phase-locked loop oscillator according to claim 4, wherein said means for obtaining said second digital value includes;

a phase comparator for outputting a signal indicating a phase difference between said input signal and said output signal;

a phase difference measuring circuit for measuring the phase difference between said input signal and said output signal on the basis of the signal output from said phase comparator; and

a moving-average circuit for obtaining said second digital value by taking the moving average of phase difference values measured by said phase difference measuring circuit.

6. A phase-locked loop oscillator according to claim 5, wherein said moving-average circuit includes;

a storage circuit for storing a predetermined number of successive numeric values, and for outputting in sequence all the numeric values stored therein each time the stored contents thereof are updated with entry of a new numeric value; and

an accumulator circuit for successively adding up the numeric values serially output from said storage circuit, said accumulator circuit being cleared when the stored contents of said storage circuit are updated.

7. A phase-locked loop oscillator according to claim 5, wherein said synchronization condition judging means judges the condition to be a synchronized condition when the difference between said first digital value and said center control value is within a predetermined range, and to be an out-of-synchronization condition when said measured phase difference value is greater than a predetermined value or when said second digital value is greater than a predetermined value.

8. A phase-locked loop oscillator according to claim 5, wherein a number of moving-average samples in said moving-average circuit is changed in accordance with the phase difference value measured by said phase difference measuring circuit.

9. A phase-locked loop oscillator according to claim 1, wherein said frequency divider control signal generating means includes;

multiple control signal generating means for generating multiple control signals from said control value; and

a selector for selecting one of said multiple control signals on the basis of said second digital value and for supplying said selected control signal to said dual-modulus frequency divider.

10. A phase-locked loop oscillator according to claim 9, wherein said multiple control signal generating means comprises;

a calculating circuit that, from the input control value, successively calculates quotients a₀, a₁, a₂ . . . a_m for output, when said control value is expressed as 1/(a₀ +1/(a₁ +1/(a₂ + . . . +1/a_m)) . . . ); and

a control signal generating circuit that includes a cascaded chain of a plurality of programmable frequency dividers in which said plurality of quotients a₀, a₁, a₂ . . . a_m are set as respective division ratios, and that frequency-divides a reference signal through the cascaded chain of said plurality of programmable frequency dividers and outputs the result as said control signal.

11. A phase-locked loop oscillator according to claim 10, wherein said calculating circuit first calculates the quotient a₀ by dividing the denominator of a fraction, corresponding to said control value, by the numerator thereof, and then successively calculates the quotients a₁, a₂ . . . a_m by repeating the process of dividing the previous divisor by the previous remainder until the remainder becomes zero.

12. A phase-locked loop oscillator according to claim 10, wherein said control signal generating circuit includes a plurality of programmable frequency dividers D₀, D₁ . . . D_m in which the quotients a₀, a₁ . . . a_m output from said calculating circuit are set as respective division ratios, the operation of said control signal generating circuit being such that the frequency divider D₀ frequency-divides the reference signal and outputs the resulting frequency-divided output d₀ as said control signal, that a frequency divider D_i, where i is an integer larger than 1 and smaller than m-1, frequency-divides a frequency-divided output d_i-1 of a frequency divider D_i-1 and supplies the resulting frequency-divided output d_i to a frequency divider D_i+1 while periodically changing the division ratio of the frequency divider D_i-1 to a_i-1 +1 with said frequency-divided output d_i, and that the frequency divider D_m frequency-divides a frequency-divided output d_m-1 of a frequency divider D_m-1 and periodically changes the division ratio of the frequency divider D_m-1 with the resulting frequency-divided output d_m.

13. A phase-locked loop oscillator according to claim 11, wherein said calculating circuit includes;

a divider circuit for dividing a dividend by a divisor and outputting a quotient and a remainder;

a first latch circuit for latching an input numeric value and outputting the same as a dividend to said divider circuit;

a second latch circuit for latching an input numeric value and outputting the same as a divisor to said divider circuit,

a first selector circuit for selecting one or the other of two inputs, the value of said denominator or the output of said second latch circuit, for supply to said first latch circuit; and

a second selector circuit for selecting one or the other of two inputs, the value of said numerator or the remainder output of said divider circuit, for supply to said second latch circuit.

14. A moving-average circuit comprising;

a storage circuit for storing a predetermined number of successive numeric values, and for individually and serially outputting all the numeric values stored therein each time the stored contents thereof are updated with entry of a new numeric value; and

a single accumulator circuit for successively adding up the numeric values serially output from said storage circuit, said accumulator circuit being cleared when the stored contents of said storage circuit is updated,

wherein said storage circuit has;

a data holding circuit including a plurality of data latch circuits connected in series, each for latching and outputting an input numeric value, a number of said data latch circuits being equal to said predetermined number of numeric values; and

a selector circuit for selecting a new numeric value for input to said data holding circuit when updating the stored contents of said storage circuit, and selecting an output of said data holding circuit for input to said data holding circuit when sequentially outputting the numeric values stored in said storage circuit.

15. A moving-average circuit according to claim 14, wherein said accumulator circuit includes;

a data latch circuit for latching and outputting an input numeric value, said data latch circuit being cleared when the stored contents of said storage circuit is updated; and

an adder circuit for adding together the numeric values output from said storage circuit and said data latch circuit and for applying the result of the addition to an input of said data latch circuit.

16. A division-ratio equalization circuit for generating a control signal by which a dual-modulus frequency divider, capable of operating with a division ratio selected from two division ratios in accordance with a control signal and controlled so that the division ratio is equally distributed along the time axis in accordance with an input control value, comprising;

a calculating circuit that, from the input control value, successively calculates quotients a₀, a₁, a₂ . . . a_m for output, when said control value is expressed as 1/(a₀ +1/(a₁ +1/(a₂ + . . . +1/a_m)) . . . ); and

a control signal generating circuit that includes a cascaded chain of a plurality of programmable frequency dividers in which said plurality of quotients a₀, a₁, a₂ . . . a_m are set as respective division ratios, and that frequency-divides a reference signal through the cascaded chain of said plurality of programmable frequency dividers and outputs the result as said control signal.

17. A division-ratio equalization circuit according to claim 16, wherein said calculating circuit first calculates the quotient a₀ by dividing the denominator of a fraction, corresponding to said control value, by the numerator thereof, and then successively calculates the quotients a₁, a₂ . . . a_m by repeating the process of dividing the previous divisor by the previous remainder until the remainder becomes zero.

18. A division-ratio equalization circuit according to claim 16, wherein said control signal generating circuit includes a plurality of programmable frequency dividers D₀, D₁ . . . D_m in which the quotients a₀, a₁ . . . a_m output from said calculating circuit are set as respective division ratios, the operation of said control signal generating circuit being such that the frequency divider D₀ frequency-divides the reference signal and outputs the resulting frequency-divided output d₀ as said control signal, that a frequency divider D_i, where i is an integer larger than 1 and smaller than m-1, frequency-divides a frequency-divided output d_i-1 of a frequency divider D_i-1 and supplies the resulting frequency-divided output d_i to a frequency divider D_i+1 while periodically changing the division ratio of the frequency divider D_i-1 to a_i-1 +1 with said frequency-divided output d_i, and that the frequency divider D_m frequency-divides a frequency-divided output d_m-1 of a frequency divider D_m-1 and periodically changes the division ratio of the frequency divider D_m-1 with the resulting frequency-divided output d_m.

19. A division-ratio equalization circuit according to claim 18, wherein said calculating circuit includes;

a divider circuit for dividing a dividend by a divisor and outputting a quotient and a remainder;

a first latch circuit for latching an input numeric value and outputting the same as a dividend to said divider circuit,

a second latch circuit for latching an input numeric value and outputting the same as a divisor to said divider circuit,

a first selector circuit for selecting one or the other of two inputs, the value of said denominator or the output of said second latch circuit, for supply to said first latch circuit; and

a second selector circuit for selecting one or the other of two inputs, the value of said numerator or the remainder output of said divider circuit, for supply to said second latch circuit.