Charge pump circuit with symmetrical current output for phase-controlled loop system

• US 5,508,660 A
• Filed: 04/25/1995
• Issued: 04/16/1996
• Est. Priority Date: 10/05/1993
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gersbach, John E., Novof, Ilya I.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US08/428,391
• Time in Patent Office: 357 Days
• Field of Search: 331/17, 331/25, 331/8, 331/1 A, 307/514, 328/135, 327/157, 327/536, 327/537, 327/538
• US Class Current: 331/17
• CPC Class Codes: H03L 7/0895 Details of the current generators H03L7/0893 takes precedence
• CPC Class Codes: H03L 7/0896 the current generators being controlled by differential up-down pulses

Abstract

A phase-controlled loop system having a charge pump circuit including a current mismatch measurement circuit and a current compensation circuit for equalizing the amplitude of positive current pulses and the amplitude of negative current pulses output when the phase-controlled loop system is in phase-locked condition. The current mismatch measurement circuit includes duplicate complementary current sources with characteristics and biasing substantially identical to that of the primary current sources providing the positive current and the negative current to the output node of the charge pump circuit. At the common connected node between the duplicate complementary current sources an error current is produced having an amplitude equal to the difference between the amplitude of the positive current pulses and the amplitude of the negative current pulses to the output node. Current mirrors then reflect this error current back to either the positive current source or the negative current source for combining with the positive current or negative current, respectively, such that the currents'"'"' amplitudes at the output node substantially cancel. Various current mismatch measurement circuit and current compensation circuit embodiments are described, including a time multiplexed sensing and compensation approach.

Claims

1. A current source circuit for use in a phase-controlled loop system having a filter, said current source circuit comprising:

an output node coupled to the filter so as to provide a control voltage thereto;

a primary pair of complementary current sources connected to the output node, each current source of said primary pair of complementary current sources supplying a different one of a positive current and a negative current to said output node, said positive current and said negative current each having an amplitude dependent upon the control voltage at the output node when in a phase-locked condition; and

feedback means for continuously sensing an amplitude difference between the amplitude of the positive current and the amplitude of the negative current when the phase-controlled loop system is in phase-locked condition and for compensating at the output node for said amplitude difference such that the amplitude difference between the positive current and the negative current supplied by said primary pair of complementary current sources is canceled when the phase-controlled loop system is in said phase-locked condition.

2. The current source circuit of claim 1, wherein said feedback means includes means for producing an error current having an amplitude equal to the difference between the amplitude of the positive current and the amplitude of the negative current when the phase-controlled loop system is in said phase-locked condition, and means for providing the error current to the output node such that the amplitude difference is canceled.

3. The current source circuit of claim 2, wherein said feedback means includes a secondary pair of complementary current sources connected to produce identical positive and negative currents to the positive and negative currents, respectively, produced by said primary pair of complementary current sources when the phase-controlled loop system is in said phase-locked condition, said feedback means including a current mismatch measurement circuit for determining the current mismatch between the positive current and the negative current of the secondary pair of complementary current sources.

4. The current source circuit of claim 3, wherein the current sources of said secondary pair of complementary current sources are connected in series with a common node therebetween, and wherein said feedback means further includes a voltage follower circuit connected between the output node and the common node of said secondary pair of complementary current sources for translating the control voltage at the output node to the common node.

5. The current source circuit of claim 4, wherein said voltage follower circuit comprises an operational amplifier having a first input connected to the output node and a second input connected to the common node of said secondary pair of complementary current sources, an output of said operational amplifier being connected to a source follower circuit, said source follower circuit also being connected to said common node of said secondary pair of complementary current sources.

6. The current source circuit of claim 2, wherein said means for providing the error current to the output node includes a first current mirror feedback circuit and a second current mirror feedback circuit, said first current mirror feedback circuit being connected to reflect said error signal to the output node when said error signal comprises a positive feedback current and said second current mirror feedback circuit being connected to reflect said error signal to the output node when said error signal comprises a negative feedback current.

7. The current source circuit of claim 1, further comprising a first switch means and a second switch means, said first switch means being connected to control the positive current output to the output node produced by a current source of the primary pair of complementary current sources and said second switch means being connected to control the negative current output to the output node produced by the other current source of said primary pair of complementary current sources, said feedback means being coupled to said primary pair of complementary current sources such that said first switch means controls transfer of positive feedback current to the output node and said second switch means controls transfer of negative feedback current to the output node.

8. The current source circuit of claim 1, wherein said feedback means includes means for time multiplexing the positive current and the negative current produced by the primary pair of complementary current sources between the output node and the means for sensing the amplitude difference between the amplitude of the positive current and the amplitude of the negative current when the phase-controlled loop system is in phase-locked condition.

9. The current source circuit of claim 8, wherein said means for compensating for the amplitude difference includes means for producing a correction value, and wherein said time multiplexing means includes a capacitor to hold the correction value when the positive current and the negative current are time multiplexed to the output node.

10. The current source circuit of claim 1, wherein said phase-controlled loop system comprises a phase-locked loop (PLL) system wherein the control voltage provided by the output node drives a voltage controlled oscillator which provides an output clock signal.

11. A current source circuit for use in a phase-controlled loop system having a filter, said current source circuit comprising:

an output node coupled to the filter so as to provide a control voltage thereto;

a charge pump having means for sourcing a positive current to the output node and means for sourcing a negative current from the output node, said positive current and said negative current each having an amplitude dependent upon the control voltage at the output node; and

feedback means for continuously sensing an amplitude difference between the amplitude of the positive current and the amplitude of the negative current when the phase-controlled system is in a phase-locked condition and for compensating at the output node for said amplitude difference so that the amplitude difference between the positive current and the negative current supplied by the charge pump is canceled at the output node when the phase-controlled loop system is in phase-locked condition.

12. The current source circuit of claim 11, wherein said feedback means for compensating at the output node for said difference includes means for producing an error current having an amplitude equal to said amplitude difference and means for providing the error current to the output node such that the amplitude difference is canceled at the output node when the phase-controlled loop system is in phase-locked condition.

13. The current source circuit of claim 12, wherein said feedback means for sensing the amplitude difference includes a current mismatch measurement circuit, said current mismatch measurement circuit having a voltage follower circuit connected to the output node.

14. The current source circuit of claim 11, wherein said feedback means for sensing the amplitude difference includes a current mismatch measurement circuit and means for time multiplexing the positive current and the negative current sourced by said charge pump between the output node and said current mismatch measurement circuit.

15. A phase-locked loop (PLL) system for providing an output signal in phase with a received reference signal, said PLL system comprising:

a phase comparator having a first input and a second input, said first input being coupled to receive the reference signal and said second input being coupled to receive as feedback the output signal, said phase comparator including means for comparing the phases of the reference signal and the output signal and for selectively providing one of a charge increase command and a charge decrease command;

a filter having a filter node;

a voltage controlled oscillator coupled to said filter for providing the output signal in response to a control voltage applied to the filter node; and

a charge pump coupled between said phase comparator and said filter for applying the control voltage to the filter and having an output node connected to the filter node, and means for sourcing a positive current to the output node in response to a charge increase command and means for sourcing a negative current from the output node in response to a charge decrease command, said charge pump further including feedback means for continuously sensing an amplitude difference between the amplitude of the positive current and the amplitude of the negative current when the PLL system is in a phase-locked condition and for compensating at the output node for said amplitude difference such that positive and negative currents of equal amplitude appear at the output node of said charge pump when the PLL system is in said phase-locked condition.

16. The PLL system of claim 15, wherein said feedback means includes means for producing an error signal having an amplitude equal to the difference between the amplitude of the positive current and the amplitude of the negative current and means for providing the error signal to the output node such that the amplitude difference between the positive current and the negative current is canceled when the PLL system is in said phase-locked condition.

17. The PLL system of claim 16, wherein said means for providing the error signal to the output node includes a first current mirror feedback circuit and a second current mirror feedback circuit, said first current mirror feedback circuit being connected to reflect said error signal to the output node when said error signal comprises a positive feedback current and said second current mirror feedback circuit being connected to reflect said error signal to the output node when said error signal comprises a negative feedback current.

18. The PLL system of claim 15, wherein said charge pump'"'"'s means for sourcing a positive current to the output node in response to a charge increase command and means for sourcing a negative current to the output node in response to a charge decrease command includes a primary pair of complementary current sources connected to the output node, each current source of said primary pair of complementary current sources supplying a different one of said positive current and said negative current to said output node.

19. The PLL system of claim 18, wherein said charge pump'"'"'s feedback means also includes a secondary pair of complementary current sources connected to produce identical positive and negative currents to the positive and negative currents, respectively, produced by said primary pair of complementary current sources when the PLL system is in said phase-locked condition, said feedback means including a current mismatch measurement circuit for determining the current mismatch between the positive current and the negative current of the secondary pair of complementary current sources.

20. The PLL system of claim 19, wherein the current sources of said secondary pair of complementary current sources are connected in series with a common node therebetween, and wherein said feedback means further includes a voltage follower circuit connected between the output node and the common node of said secondary pair of complementary current sources for translating the control voltage at the output node to the common node.