PHASE-LOCKED LOOP, PHASE COMPARATOR FOR USE IN THE PHASE-LOCKED LOOP, AND REPRODUCING DEVICE INCLUDING THE PHASE-LOCKED LOOP

Abstract: A phase-locked loop comprises an input terminal (1) for receiving a binary signal, a phase comparator (3) having a first input (2) coupled to the input terminal (1), having a second input (4), and having an output (5) coupled to an input (9) of a control-signal-controlled oscillator (10) via a control-signal generator unit (7). An output (11) of the oscillator is coupled to the second input of the phase comparator. The phase comparator is adapted to derive a first pulse (P1) and a second pulse (P2) in response to a signal transition from a first value to a second value in the binary signal applied to the first input and an oscillation signal applied to the second input, which first pulse has a pulse width which is a measure of the phase difference between the binary signal and the oscillation signal and which second pulse has a pulse width proportional to 1/2.fo, where fo is said frequency of the oscillation signal. The control-signal generator unit (7) is adapted to derive a control signal from the first and the second pulse and to apply the control signal to the oscillator, and the control-signal generator unit is adapted to derive such a control signal from the first and the second pulse that the phase difference is controlled substantially toward zero.

Description: Phase-locked loop, phase comparator for use in the phase-locked loop, and reproducing device including the phase-locked loop. The invention relates to a phase-locked loop comprising - an input terminal for receiving a binary signal, - a phase comparator having a first input coupled to the input terminal, having a second input, and having an output, - a control-signal-controlled oscillator having an input for receiving a control signal, which input is coupled to the output of the phase comparator, and an output for supplying an oscillation signal of a given frequency in response to the control signal, which output is coupled to the second input of the phase comparator, and the invention also relates to a phase comparator for use in the phase-locked loop and to a reproducing device including the phase- locked loop. A phase-locked loop of the type defined in the opening paragraph is generally known and is used to derive a clock signal from the binary signal. The binary signal may be an originally digital signal recorded on a record carrier. Upon reproduction an analog reproduction signal is obtained which is converted into a binary signal in a comparator circuit, which binary signal is then applied to the phase-locked loop. The clock signal can subsequently be used to recover the original digital signal during reproduction. The known phase-locked loop has the drawback that variations in the nominal oscillator frequency of the oscillator give rise to timing errors in the clock signal. It is an object of the invention to provide a phase-locked loop which is less susceptible to timing errors. To this end the phase-locked loop in accordance with the invention is characterised in that the phase comparator is adapted to derive a first pulse and a second pulse in response to a signal transition from a first value to a second value in the binary signal applied to the first input and the oscillation signal applied to the second input, which first pulse has a pulse width which is a measure of the phase difference between the binary signal and the oscillation signal and which second pulse has a pulse width proportional to 1/2. f 0 , where f 0 is said frequency of the oscillation signal, in that the phase-locked loop has a control-signal generator unit coupled to a phase comparator, for deriving a control signal from the first and the second pulse and for applying the control signal to an output, which output is coupled to the input of the oscillator, and in that the control-signal generator unit is adapted to derive such a control signal from the first and the second pulse that the phase difference is controlled substantially toward zero. The invention is based on the recognition of the fact that a first pulse is obtained which is a measure of the phase difference, whereas the second pulse may a be regarded as a reference pulse. However, this reference pulse is not constant but varies with the variations in the clock frequency of the oscillator. Embodiments of the invention will now be described in more detail, by way of example, with reference to the drawings. In the drawings Figure 1 shows a first embodiment of the phase-locked loop, Figure 2 shows the phase comparator in the loop of Figure 1 in greater detail, Figures 3, 4 and 5 show signal patterns which occur in the arrangement of Figure 2 for zero phase difference, a positive phase difference and a negative phase difference, respectively, between the binary signal and the clock signal, Figure 6 shows a second, Figure 7 shows a third, Figure 8 shows a fourth, Figure 9 shows a fifth embodiment of the phase comparator, Figure 10 shows an example of the control-signal generator unit, Figure 11 shows an example of a data detector including the phase comparator shown in Fig. 2, and Figure 12 shows some signal waveforms appearing in the data detector shown in Fig. 11. Figure 1 shows a phase-locked loop to which a binary signal can be applied via an input terminal 1. The terminal 1 is coupled to a first input 2 of a phase comparator 3, which has an output 5 coupled to an input 6 of a control-signal generator unit 7. The output 8 of the unit 7 is coupled to an input 9 of a control-signal-controlled oscillator 10, for example, a voltage-controlled oscillator. The output 11 of the oscillator 10 is coupled to a second input 4 of the phase comparator. Figure 2 shows the phase comparator of Figure 1 in greater detail. The phase comparator 3a in Figure 2 comprises a first flip-flop 15 and a second flip-flop 16. In the present example the flip-flops are D flip-flops. The first input 2 of the phase comparator 3a is coupled to a first input 17 of the flip-flop 15, which is the D input of the flip-flop. An output 21 of the flip-flop 15 is coupled to a first input 22 of the second flip-flop 16, i.e. the D input of this flip-flop. The second input 4 of the phase comparator 3a is coupled to a second input 18 of the first flip-flop and, via an inverting element 20, to a second input 19 of the second flip-flop. These second inputs of the flip-flops are the clock inputs of the two flip- flops. The output 21 of the flip-flop 15 and an output 23 of the flip-flop 16 are coupled to inputs of a first gate circuit 24, in the present example an exclusive-or circuit. The first input 17 and the output 21 of the flip-flop 15 are coupled to inputs of a second gate circuit 25, in the present example an exclusive-or circuit. The output of the gate 25 is coupled to a first output 5.1 of the phase comparator 3a. The output of the gate 24 is coupled to a second output 5.2 of the phase comparator 3a. The output 5 in Figure 1 thus comprises two sub- outputs 5, land 5.2 coupled to corresponding sub-inputs 6.1 and 6.2 (not shown) of the generator unit 7. Figure 3 illustrates the operation of the phase comparator shown in Figure 2. The signal (a) in Figure 3 shows the binary input signal, which is applied to the input terminal 1, as a function of time. The signal has a rising edge followed by a falling edge. The signal (b) in Figure 3 is the clock signal applied to the input 4 of the phase comparator 3a. The period of the clock signal is T and the duty cycle of the clock signal is 50 %. The period T complies with the relationship T = l/f 0 , where f c is the clock frequency of the clock signal supplied by the oscillator 10. The signal (c) is the output signal Q, at the output 21 of the flip-flop 15. As a result of these signals the signal UP appears, see (d) in Figure 3, at the output 5.1. The signal (e) is the output signal Q 2 at the output 23 of the flip- flop 16. As a result, the signal DOWN, see (0 in Figure 3, appears at the output 5.2. The rising edge in the signal (a) in Figure 3 results in a first pulse, the pulse P,, in the UP signal and a second pulse, the pulse P 2 , in the DOWN signal. The falling edge in the signal (a) in Figure 3 results in a third pulse, the pulse P 3 , in the UP signal and a fourth pulse, the pulse P 4 , in the DOWN signal. In the present example the spacing between the edges in the binary signal (a) in Figure 3 is equal to T. The situation in Figure 3 is the situation in which the phase difference is 0. In the present example this means that the rising edge E„ in (b) in Figure (3) appears a time interval equal to T/2 after the rising edge in the binary signal (a) in Figure 3. This rising edge E„ can be used for recovering the digital signal. In the example of Figure 3 it appears that the four pulses P, to P 4 all have the same width, i.e. T/2. What has been said in the preceding paragraph about the rising edge in the signal (a) in Figure 3 also applies to the falling edge in this signal. Moreover, it is to be noted that the width of the pulses P 2 and P 4 is T/2 in the present example but that this is not strictly necessary. The width of the pulses may deviate from the value T/2, provided that the pulse width is proportional to 1 divided by the oscillation frequency f 0 . Thus, the width could be, for example, T/3 or 2T/3. In that case the rising edge E„ will appear a time interval equal to T/3 (or 2T/3) after the rising edge in the binary signal (a) in Figure 3. Pulse widths of T/4, 5T/16, 3T/8, 7T/16, 9T/16, 5T/8, 11T/16 or 3T/4 could also be considered. However, the width of the pulses P 2 and P 4 should not be too small or too large, i.e. not too close to T, since the this would result in asymmetric control. The control-signal generator unit 7 is adapted to derive from the pulses P, to P 4 a control signal which is applied to the voltage-controlled oscillator. In an example of the generator unit 7 the pulses PI to P4 are integrated, the pulses P 2 and P 4 first being given a negative sign. In the case of Figure 3 the results in a control signal change equal to 0, so that the frequency of the oscillation signal does not change. It is to be noted here that the generator unit 7 can already derive a control signal and apply this to the oscillator 10 on the basis of the integrated values of the pulses P j and P 2 , after a rising edge has appeared in the binary signal. Likewise, the control- signal generator unit can derive a control signal and apply this to the oscillator 10 on the basis of the integrated values of the pulses P 3 and P 4 , after a falling edge has appeared in the binary signal. Figure 4 represents a situation in which there is a positive phase difference άφ between the binary signal and the oscillation signal. This is visible in (b) in Figure 4 in that the rising edge E,, in the oscillation signal appears later than the instant , which occurs a time interval T/2 after the rising edge in the binary signal (a) in Figure 4. It is now essential that the pulses P 2 and P 4 still have a width equal to T/2, whereas the pulses P, and P 3 are wider by an amount equal to the phase difference άφ. The integration of the pulses P, and P 2 as stated above (and likewise the integration of the pulses P, and P 3 and the integration of the pulses P 2 and P 4 ) yields a positive change in value at the output 8 of the generator unit 7. The oscillation frequency will increase in response to this, as a result of which the rising edge E u will move to the left in (b) in Figure 4 until the phase difference άφ is substantially zero. Figure 5 illustrates a situation in which there is a negative phase difference άφ between the binary signal and the oscillation signal. This is visible in (b) in Figure 5 in that the rising edge E,, in the oscillation signal appears earlier than the instant t b , which occurs a time interval T/2 after the rising edge in the binary signal (a) in Figure 5. It is again essential that the pulses P 2 and P 4 still have a width equal to T/2, whereas the pulses P, and P 3 are narrower by an amount equal to the phase difference άφ. The integration of the pulses P, and P 2 as stated above (and likewise the integration of the pulses P, and P 3 and the integration of the pulses P 2 and P 4 ) now yields a negative change in value at the output 8 of the generator unit 7. The oscillation frequency will decrease in response to this, as a result of which the rising edge E„ will move to the right in (b) in Figure 5 until the phase difference άφ is substantially zero. It is obvious that the width of the pulses P 2 and P 4 also varies in the case of a varying oscillator frequency f 0 . Timing errors in the circuit arrangement shown in Figure 2 can be precluded by matching the inherent delay of the inverter 20 to that of the flip-flops 15 and 16. Another possibility is to provide an additional delay in the connection from the terminal 2 to the input of the gate circuit 25, which delay should then be substantially equal to the propagation delay from the CK input 18 to the Q output 21 of the flip-flop 15. Figure 6 shows a second embodiment of the phase comparator. The phase comparator 3b in Figure 6 bears much resemblance to the phase comparator 3a in Figure 2. The inverting element 20 in Figure 2 is absent in Figure 6. Moreover, there is provided a third gate circuit 30, in the form of an and gate. The and gate 30 has one input coupled to the input 4 of the phase comparator and its other input to the output of the gate 24. The output of the and gate 30 is now coupled to the second output 5.2. Figure 7 shows a third embodiment of the phase comparator. The phase comparator 3c again comprises a first flip-flop 15 and a second flip-flop 16. The first input 2 of the phase comparator 3c is now coupled to the reset input 43 of the flip-flop 15 via a series arrangement of two inverting elements 40 and 41 and an exclusive-or gate 42. The inverting elements 40 and 41 operate as a delay unit and in conjunction with the exclusive-or gate 42 they are intended to serve as edge detector for the VCO signal. The output 21 of the flip-flop 15 is again coupled to the first input 22 of the second flip-flop 16, which is the D input of this flip-flop. The second input 4 of the phase comparator 3c is again coupled to the clock input 18 of the first flip-flop and to the clock input 19 of the second flip-flop. The output 21 of the flip-flop 15 is coupled to the first output 5.1 of the phase comparator 3c via an inverting element 45. The output 23 of the flip- flop 16 and the input 4 are coupled to inputs of a gate circuit 46, in the present example a nand circuit. The output of the gate 46 is coupled to the second output 5.2 of the phase comparator 3c. A logic "1" is applied to the input 17 of the flip-flop 15. Figure 8 shows yet another embodiment of the phase comparator. The phase comparator 3d in Figure 8 again comprises a first flip-flop 15 and a second flip-flop 16. The first input 2 of the phase comparator 3d is now coupled to the clock input 18 of the flip-flop 15 via an edge detection circuit 50. The output 21 of the flip-flop 15 is again coupled to the first input 22 of the second flip-flop 16, which is the D input of this flip-flop. The second input 4 of the phase comparator 3d is now coupled to the reset input 43 of the first flip-flop via the series arrangement of two inverting elements 40 and 41 and an exclusive-or gate 42 and to the clock input 19 of the second flip-flop 16. The output 21 of the flip-flop 15 is coupled to the first output 5.1 of the phase comparator 3c to supply the UP signal. The output 23 of the flip-flop 16 and the input 4 are coupled to inputs of a gate circuit 52, in the present example an and circuit. The output of the gate 52 is coupled to the second output 5.2 of the phase comparator 3d. Again, a logic "1" is applied to the input 17 of the flip-flop 15. Figure 9 shows still another embodiment of the phase comparator. The phase comparator 3e in Figure 9 again comprises a first flip-flop 15 and a second flip-flop 16. The first input 2 of the phase comparator 3e is again coupled to the clock input 18 of the flip-flop 15 via an edge detection circuit 50. The edge detection circuit supplies a pulse of a given width upon detection of a rising or a falling edge in the binary input signal. The output 21 of the flip-flop 15 is again coupled to the D input 22 of the second flip-flop 16. The second input 4 of the phase comparator 3e is now coupled to the reset input 43 of the first flip-flop via a series arrangement of an inverting element 40 and an and gate 5, and to the clock input 19 of the second flip-flop 16. The output 21 of the flip-flop 15 is again coupled to the first output 5.1 of the phase comparator 3e to supply the UP signal. The output 23 of the flip-flop 16 and the input 4 are coupled to inputs of a gate circuit 52, in the present example again an and circuit. The output of the gate 52 is coupled to the second output 5.2 of the phase comparator 3e. Again, a logic "1 " is applied to the input 17 of the flip-flop 15. The elements 40 and 55 again operate as an edge detector, in the present case for the rising edges in the VCO signal. Figure 10 shows an example of the signal generator unit 7. The generator unit, referenced 7a in the present example, comprises a signal combining unit 62, in the form of a subtracter circuit, having a first and a second input coupled to the first input 6.a and the second input 6.b, respectively, and an integrating element 60, coupled between the output of the combining unit 62 and the output 8. It is obvious that the signal combining unit 62 may form part of the phase comparator. In that case the phase comparator has only one output 5 instead of two sub-outputs 5.1 and 5.2. Figure 11 shows an example of a data detector for the detection of bits in a signal which has been read from a record carrier 70. The data detector is a detector of the PR IV type, i.e. partial response class 4, or of the Nyquist 1 type. The detector has two branches 72 and 74. The branch 72 is intended for the detection of positive pulses and the branch 74 is intended for the detection of negative pulses in the signal V^ read from the record carrier 70. The signal V to is applied to threshold comparators 76 and 78 in the two branches. The output of the threshold comparator 76 is coupled to an input of a phase comparator 80 as shown in Figure 2. The output of the threshold comparator 78 is coupled to an input of a phase comparator 82 as shown in Figure 2. The Q outputs of the flip-flops 15 and 15' in the phase comparators 80 and 82, respectively, are coupled to inputs of an OR gate 86, which has an output coupled to an output terminal 88. The outputs 5.1 and 5.2 of the gate circuits 24 and 25 of the phase comparator 80 and the outputs 85.1 and 85.2 of the gate circuits 24' and 25' of the phase comparator 82 are coupled to inputs of a signal combination unit 90, which has an output coupled to an input of a loop filter 92, which forms part of the unit 7 in Figure 1. The signal V^ is shown in (a) in Figure 12. Comparison of the signal V^ with the thresholds V,., and V ra results in signals as shown in (b) and (c), respectively, in Figure 12 appearing at the outputs of the threshold comparators 76 and 78, respectively. At the Q outputs of the flip-flops 15 and 15' signals D p and D n appear, which are shown in (d) and (e) in Figure 12. The actual data signal D o ,,, as shown in (f) in Figure 12 appears at the output of the OR gate 86. The output signal of the oscillator (10) is shown in (g) in Figure 12. The rising edges in this signal are the clock instants at which the signal V^ in (a) of Figure 12 is sampled. The detection is such that if at a clock instant V m has a value larger than V,., or larger than V m (in the negative direction) it is determined that the transmitted bit is an " 1 " bit or otherwise a "0". This results in the signal D ^ , in (f) in Figure 12.

Claims: Claims: 1. A phase-locked loop comprising - an input terminal for receiving a binary signal, - a phase comparator having a first input coupled to the input terminal, having a second input, and having an output, - a control-signal-controlled oscillator having an input for receiving a control signal, which input is coupled to the output of the phase comparator, and an output for supplying an oscillation signal of a given frequency in response to the control signal, which output is coupled to the second input of the phase comparator, characterised in that the phase comparator is adapted to derive a first pulse and a second pulse in response to a signal transition from a first value to a second value in the binary signal applied to the first input and the oscillation signal applied to the second input, which first pulse has a pulse width which is a measure of the phase difference between the binary signal and the oscillation signal and which second pulse has a pulse width proportional to 1/2. f 0 , where f 0 is said frequency of the oscillation signal, in that the phase-locked loop has a control-signal generator unit coupled to a phase comparator, for deriving a control signal from the first and the second pulse and for applying the control signal to an output, which output is coupled to the input of the oscillator, and in that the control-signal generator unit is adapted to derive such a control signal from the first and the second pulse that the phase difference is controlled substantially toward zero. 2. A phase-locked loop as claimed in Claim 1, characterised in that the phase comparator has a first and a second output for supplying the first pulse and the second pulse, respectively, and the control-signal generator unit has a first and a second input coupled to the first output and the second output, respectively, of the phase comparator. 3. A phase-locked loop as claimed in Claim 1, characterised in that the phase comparator is further adapted to derive a third pulse and a fourth pulse in response to a subsequent signal transition from the second value to the first value in the binary signal applied to the first input and the oscillation signal applied to the second input, which third pulse has a pulse width which is a measure of the phase difference between the binary signal and the oscillation signal, and which fourth pulse has a pulse width proportional to 1/2. , in that the control-signal generator unit is further adapted to derive from the first, the second, the third and the fourth pulse a control signal and to supply the control signal to the output, and in that the control-signal generator unit is adapted to derive such a control signal from the first, the second, the third and the fourth pulse that the phase difference is controlled substantially toward zero. 4. A phase-locked loop as claimed in Claim 3, characterised in that the phase comparator has a first output for supplying the first and the third pulse and a second output for supplying the second and the fourth pulse, and the control-signal generator unit has a first and a second input coupled to the first output and the second output, respectively, of the phase comparator. 5. A phase-locked loop as claimed in any one of the preceding Claims, characterised in that the phase comparator comprises a first and a second flip-flop, each flip- flop having a first and a second input and an output, in that the first and the second input of the phase comparator are coupled to the first and the second input, respectively, of the first flip-flop, the output of the first flip-flop is coupled to both the first input of the second flip- flop and the first output of the phase comparator, the second input of the phase comparator is coupled to the second input of the second flip-flop, and the output of the second flip-flop is coupled to the second output of the phase comparator. 6. A phase-locked loop as claimed in Claim 5, characterised in that the phase comparator comprises a first gate circuit having a first and a second input coupled to the output of the first and the second flip-flop, respectively, and having an output coupled to the second output of the phase comparator. 7. A phase-locked loop as claimed in Claim 6, characterised in that the phase comparator comprises a second gate circuit having a first and a second input coupled to the first input and the output, respectively, of the first flip-flop, and having an output coupled to the first output of the phase comparator. 8. A phase-locked loop as claimed in Claim 7, characterised in that the phase comparator comprises a third gate circuit having a first and a second input coupled to the second input of the phase comparator and the output of the first gate circuit, respectively, and having an output coupled to the second output of the phase comparator. 9. A phase-locked loop as claimed in Claim 5, characterised in that the second input of the phase comparator is coupled to the second input of the second flip-flop via an inverting element. 10 10. A phase-locked loop as claimed in Claim 5, characterised in that the phase comparator comprises a first gate circuit having a first and a second input coupled to the second input of the phase comparator and the output of the second flip-flop, respectively, and having an output coupled to the second output of the phase comparator. 11. A phase-locked loop as claimed in Claim 10, characterised in that the second input of the phase comparator is coupled to the second inputs of the first and the second flip-flop via a second gate circuit. 12. A phase-locked loop as claimed in Claim 10, characterised in that the first input of the phase comparator is coupled to the first input of the first flip-flop via a second gate circuit. 13. A phase-locked loop as claimed in any one of the Claims 5 to 12, characterised in that the flip-flops are D flip-flops. 14. A phase-locked loop as claimed in any one of the Claims 5 to 9, characterised in that the flip-flops are D flip-flops and in that the first inputs of the flip-flops are the D inputs and the second inputs of the flip-flops are the clock inputs. 15. A phase-locked loop as claimed in Claim 14, characterised in that the first and the second gate circuit are exclusive-or gates. 16. A phase-locked loop as claimed in Claim 10 or 11, characterised in that the flip-flops are D flip-flops, and in that the first input of the first flip-flop and the second input of the second flip-flop are clock inputs, the second input of the first flip-flop is the reset input and the first input of the second flip-flop is the D input. 17. A phase-locked loop as claimed in Claim 16, characterised in that the first gate circuit is an and gate. 18. A phase-locked loop as claimed in Claim 12, characterised in that the flip-flops are D flip-flops, and in that the first input of the first flip-flop is a reset input, the second inputs of the first and the second flip-flop are clock inputs, and the first input of the second flip-flop is the D input. 19. A phase-locked loop as claimed in Claim 18, characterised in that the first gate circuit is a nor gate and the second gate circuit is an exclusive-or gate. 20. A phase-locked loop as claimed in Claim 15, characterised in that the third gate circuit is an and gate. 21. A phase-locked loop as claimed in Claim 1, characterised in that the pulse width of the second pulse is substantially equal to 1/2. f 0 . 22. A phase comparator for use in a phase-locked loop as claimed in any one of the preceding Claims, characterised by those features which in the preceding Claims characterise the phase comparator. 23. A reproducing device including a phase-locked loop as claimed in any one of the Claims 1 to 21.

Inventors: RIJCKAERT ALBERT MARIA ARNOLD, VAN VLERKEN JOHANNES JOSEPHUS, RIJCKAERT, ALBERT, MARIA, ARNOLD, VAN VLERKEN, JOHANNES, JOSEPHUS, LEONARDUS, MARIA
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1995
Main classification: H03L7
IPC codes: H03L7, H04L7