Method and apparatus for gain compensation and control in low voltage differential signaling applications

• US 6,617,925 B2
• Filed: 06/13/2002
• Issued: 09/09/2003
• Est. Priority Date: 06/14/2001
• Status: Active Grant

• Current Assignee: Arm Incorporated (SoftBank Group Corp.)
• Original Assignee: NurLogic Design, Inc. (SoftBank Group Corp.)
• Inventors: Hoang, Chinh L.
• Primary Examiner(s): NGUYEN, PATRICIA T
• Application Number:
  US10/172,206
• Publication Number:
  US 20020190795A1
• Time in Patent Office: 453 Days
• Field of Search: 330/253, 330/258
• US Class Current: 330/258
• CPC Class Codes: H03K 19/018528 with at least one differential stage
• CPC Class Codes: H04L 25/0276 Arrangements for coupling common mode signals
• CPC Class Codes: H04L 25/0292 Arrangements specific to the receiver end

Abstract

A low voltage differential signaling receiver includes a gain compensation and control circuit having a low common mode compensation circuit and a high common mode compensation circuit. A control circuit is coupled to both compensation circuits and senses the operation of one to control the operation of the other. The operation of the compensation circuits ensures that differential signals having a wide range of common mode input voltages are accurately detected by the receiver. The control circuit serves to keep the combined operation of the compensation circuits stable over the wide range of common mode input voltages.

Claims

1. A differential signaling apparatus, comprising:

a pair of input nodes that receive a differential signal having an input common mode voltage;

a pair of output nodes;

a first compensation circuit coupled to the input nodes and the output nodes, the first compensation circuit being operative to establish a first component of a differential voltage across the pair of output nodes in response to the received differential signal;

a second compensation circuit coupled to the input nodes and the output nodes, the second compensation circuit being operative to establish a second component of the differential voltage across the pair of output nodes in response to the received differential signal; and

a control circuit that senses an operational characteristic of the first compensation circuit and controls operation of the second compensation circuit in accordance with the sensed operational characteristic,

wherein the first compensation circuit is more operative at a first level of the input common mode voltage than at a second level of the input common mode voltage,

and wherein the second compensation circuit is more operative at the second level of the input common mode voltage than at the first level of the input common mode voltage.

2. A differential signaling apparatus according to claim 1, wherein the control circuit includes a replica circuit that provides an output corresponding to the sensed operational characteristic by replicating operation of the first compensation circuit.

3. A differential signaling apparatus according to claim 2, wherein the sensed operational characteristic is a bias current, the control circuit further including:

a reference current supply that produces a reference current;

a current subtractor that provides a difference current between the reference current and a current corresponding to the bias current; and

a current mirror that controls an operating current of the second compensation circuit in accordance with the difference current.

4. A differential signaling apparatus according to claim 3, wherein the control circuit and the first compensation circuit are operative such that the difference current is greater at the second level of the input common mode voltage than at the first level of the input common mode voltage.

5. A differential signaling apparatus according to claim 1, wherein the first compensation circuit includes a first pair of transistors each having a gate and a pair of source/drain terminals, the gates of the first transistors being respectively coupled to the pair of input nodes, one of the source/drain terminals of each transistor being commonly coupled to a first current supply, the other of the source/drain terminals of the first transistors being respectively coupled to the pair of output nodes.

6. A differential signaling apparatus according to claim 5, wherein the second compensation circuit includes a second pair of transistors each having a gate and a pair of source/drain terminals, the gates of the second transistors being respectively coupled to the pair of input nodes, one of the source/drain terminals of each transistor being commonly coupled to a second current supply, the other of the source/drain terminals of the second transistors being respectively coupled to the pair of output nodes.

7. A differential signaling apparatus according to claim 6, wherein the second pair of transistors has a second polarity type opposite from a first polarity type of the first pair of transistors.

8. A differential signaling apparatus according to claim 5, wherein the control circuit senses an amount of current drawn from the first current supply by the first compensation circuit and controls operation of the second compensation circuit in accordance with the sensed amount of current.

9. A differential signaling apparatus according to claim 8, wherein the control circuit includes a replica circuit of the first compensation circuit that provides an output corresponding to the sensed current by replicating operation of the first compensation circuit.

10. A differential signaling apparatus according to claim 8, wherein the control circuit includes a replica circuit of the first compensation circuit including a third pair of transistors each having a gate and a pair of source/drain terminals, the gates of the third transistors being respectively coupled to the pair of input nodes, one of the source/drain terminals of each transistor being commonly coupled to a third current supply, the other of the source/drain terminals of the third transistors being commonly coupled to a current sensing node.

11. A differential signaling apparatus according to claim 10, wherein the third pair of transistors are substantially similar to the first pair of transistors.

12. A differential signaling apparatus according to claim 10, wherein the third pair of transistors are scaled in proportion to the first pair of transistors.

13. A differential signaling apparatus according to claim 10, wherein the control circuit further includes:

a reference current supply that produces a reference current;

a current subtractor that provides a difference current between the reference current and a current corresponding to the sensed current in the replica circuit; and

a current mirror that controls an operating current of the second compensation circuit in accordance with the difference current.

14. A differential signaling apparatus according to claim 13, wherein the control circuit and the first compensation circuit are operative such that the difference current is greater at the second level of the input common mode voltage than at the first level of the input common mode voltage.

15. A differential signaling apparatus, comprising:

a pair of input nodes that receive a differential signal having an input common mode voltage;

a pair of output nodes;

a first compensation circuit coupled to the input nodes and the output nodes, the first compensation circuit being operative to establish a first component of a differential voltage across the pair of output nodes in response to the received differential signal;

a second compensation circuit coupled to the input nodes and the output nodes, the second compensation circuit being operative to establish a second component of the differential voltage across the pair of output nodes in response to the received differential signal; and

a control circuit coupled to the first and second compensation circuits;

wherein the first compensation circuit is more operative at a first level of the input common mode voltage than at a second level of the input common mode voltage,

and wherein the second compensation circuit is more operative at the second level of the input common mode voltage than at the first level of the input common mode voltage,

and wherein the control circuits adjusts the operation of the second compensation circuit at the first and second levels of the input common mode voltage in correspondence with the operation of the first compensation circuit so that a combined operation of the first and second compensation circuits is substantially the same at the first and second levels of the input common mode voltage.

16. A differential signaling apparatus, comprising:

means for receiving a differential signal having an input common mode voltage;

output means;

first means for compensating for a low level of the input common mode voltage, the first means establishing a first component of a differential voltage at the output means in response to the received differential signal;

second means for compensating for a high level of the input common mode voltage, the second means for establishing a second component of the differential voltage at the output means in response to the received differential signal;

means for sensing an operational characteristic of the first means; and

means for controlling operation of the second means in accordance with the sensed operational characteristic,

wherein the first means is more operative at the low level of the input common mode voltage than at the high level of the input common mode voltage,

and wherein the second means is more operative at the high level of the input common mode voltage than at the low level of the input common mode voltage.

17. A differential signaling apparatus according to claim 16, wherein the controlling means is operative such that a combined operation of the first and second means is substantially the same at an entire range including the low and high levels of the input common mode voltage.

18. A differential signaling method, comprising:

receiving a differential signal having an input common mode voltage;

firstly compensating for a low level of the input common mode voltage, the firstly compensating step including establishing a first component of a differential voltage in response to the received differential signal in accordance with a first operational characteristic;

secondly compensating for a high level of the input common mode voltage, the secondly compensating step including establishing a second component of the differential voltage in response to the received differential signal in accordance with a second operational characteristic;

sensing the first operational characteristic; and

controlling the second operational characteristic in accordance with the sensed first operational characteristic,

wherein the first operational characteristic is stronger at the low level of the input common mode voltage than at the high level of the input common mode voltage,

and wherein the second operational characteristic is stronger at the high level of the input common mode voltage than at the low level of the input common mode voltage.

19. A differential signaling method according to claim 18, wherein the controlling step is operative such that a combination of the first and second operational characteristics is substantially the same across an entire range including the low and high levels of the input common mode voltage.