Method and a device for phase and frequency comparison

1. A method for controlling, as a function of frequency (F ref ) and phase of a reference signal (S ref ), the frequency (F vco ) and phase of an output signal of an oscillator having a frequency control input, said method comprising the steps of:

detecting continuously in the reference signal (S ref ) and in the signal from the oscillator events representative of the frequency and the phase of that signal,

generating a first control signal at a first level (I n ) after detecting one of said events in a first signal of said reference signal and said signal from the oscillator,

generating a second control signal at the first level and of opposite polarity to the first control signal after detecting one of said events in a second signal of said reference signal and said signal from the oscillator,

applying the control signal (I o ; V o ) thus generated to the control input of the oscillator, and

halting generation of the first and second control signals if they are generated simultaneously, which method is characterized in that it further comprises the steps of:

triggering the generation of a third control signal at a second level (In+ε) after detecting one of said events in said first signal of said reference signal (S ref ) and said signal from the oscillator, if the first control signal is generated,

triggering the generation of a fourth control signal at the second level and of the opposite polarity to the third control signal after detecting one of said events in said second signal of the reference signal and the signal from the oscillator, if the second control signal is generated,

determining the control signal (I o ; V o ) to be applied to the control input of the oscillator by adding all of the control signals thus generated, and

halting generation of all the control signals if the third and fourth control signals are generated simultaneously.

2. The method according to claim 1 , characterized in that the frequency (F vco ) of the output signal of the oscillator is divided by a division ratio (N) and events in the signal from the oscillator are detected in the signal whose frequency (F vco ) has been divided by the division ratio (N).

3. The method according to claim 1 , characterized in that the second control signal level (I n +ε) is identical to the first control signal level (I n ).

4. The method according to either claim 1 or claim 2 , characterized in that the second control signal level (I n +ε) is slightly higher than the first control signal level (I n ).

5. The method according to claim 1 , characterized in that it further comprises the steps of:

generating a (2i-1) th control signal at an i th level after detecting one of said events in the first signal of said reference signal and said signal from the oscillator while the (2i-3) th control signal is generated, where i is an integer greater than 2, generating a (2i) th control signal at the i th level and of the opposite polarity to the (2i-1) th control signal after detecting one of said events in the first signal of said reference signal and said signal from the oscillator while the (2i-2) th control signal is generated, and

halting the generation of the (2i) th , (2i-1) th , (2i-2) th and (2i-3) th control signals if the (2i) th , (2i-1) th control signals are generated simultaneously.

6. The method according to claim 5 , characterized in that the i th control signal level is identical to the (I-1) th control signal level.

7. A phase and frequency comparator adapted to control the frequency of the output signal of an oscillator having a frequency control input, the comparator receiving at its input a signal (S ref ) having a reference frequency (F ref ) and a signal from the oscillator and comprising:

first detection means for detecting continuously in the reference signal (S ref ) and in the signal from the oscillator events representative of the frequency and the phase of the signal,

a first source (S 1 + ) of control signals at a first level (I n ),

a second source (S 1 − ) of control signals at the first level (I n ) and of the opposite polarity to the signal from the first source,

first switching means which when closed apply to the output of the comparator the control signal from the first source (S 1 + ) after detection of one of said events in a first signal of said reference signal and said signal from the oscillator,

second switching means which when closed apply to the output of the comparator the signal from the second source (S 1 − ) after detection of one of said events in a second signal of said reference signal and said signal from the oscillator, and

first control means for controlling the first and second switching means to place them in the open state when they are simultaneously in the closed state, which phase comparator is characterized in that it further comprises:

a third source (S 2 + ) of control signals at a second level (I n +ε),

a fourth source (S 2 − ) of control signals at the second level (I n +ε) and of the opposite polarity to the signal from the third source,

third switching means which, in the closed state when the first switching means are in the closed state, apply to the output of the comparator the control signal from the third source (S 2 + ) after detection of one of said events in the first signal of said reference signal and said signal from the oscillator,

fourth switching means which, in the closed state when the second switching means are in the closed state, apply to the output of the comparator the signal from the fourth source (S 2 − ) after detection of one of said events in the second signal said reference signal and said signal from the oscillator, the output signal (I o ) of the comparator having a level corresponding to the sum of the control signals applied by the switching means at the output of the comparator, and

second control means adapted to place the first and second switching means the open state when the third and fourth switching means are simultaneously in the closed state.

8. The phase and frequency comparator according to claim 7 , characterized in that the first and second control signal levels (I n , (I n +ε)) are constant.

9. The phase and frequency comparator according to claim 7 , characterized in that the second control signal level is slightly higher than the first control signal level.

10. The phase and frequency comparator according to claim 7 , characterized in that the signal from the oscillator applied at the input of the comparator is obtained by dividing the frequency (F vco ) of the output signal of the oscillator by a division ratio (N).

11. The phase and frequency comparator according to claim 7 , characterized in that it further comprises second detector means for continuously detecting in the reference signal (S ref ) and in the signal from the oscillator events representative of the frequency and the phase of that signal and means for activating the second detection means only if the first or the second switching means are in the closed state and for maintaining the second detection means in the closed state independently of the state of the first detection means.

12. The phase and frequency comparator according to claim 11 , characterized in that it further comprises means for maintaining the second detection means active during the change to the open state of the first and second switching means.

13. The phase and frequency comparator according to claim 7 , characterized in that it further comprises means for maintaining the first control means and the second control means in the active state until the first switching means and the second switching means and/or the third switching means and the fourth switching means have changed to the open state after triggering of the control means.

14. The phase and frequency comparator according to claim 7 , characterized in that it further comprises:

a (2i-1) th source of control signals at an i th level,

a (2i) th source of control signals at the i th level and of the opposite polarity signal from the (2i-1) th source,

(2i-1) th switching means which, in the closed state when the (2i-3) th switching means are in the closed state, apply to the output of the comparator the control signal from the (2i-1) th source after detection of one of said events in the first signal of said reference signal and said signal from the oscillator,

(2i) th switching means which, in the closed state when the (2i-2) th switching means are in the closed state, apply to the output of the comparator the signal from the (2i) th source, after detection of one of said events in the second signal of said reference signal and said signal from the oscillator, the output signal (I o ) of the comparator having a level corresponding to the sum of the control signals applied by the switching means at the output of the comparator, and

means for controlling the (2i-3) th to (2i) th switching means to place them in the open state when the (2i-1) th and (2i) th switching means are simultaneously in the closed state.