Digital transmission circuit and method providing selectable power consumption via single-ended or differential operation

• US 20060171477A1
• Filed: 02/03/2005
• Published: 08/03/2006
• Est. Priority Date: 02/03/2005
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Carballo, Juan-Antonio, Nowka, Kevin John, Vo, Ivan, Yoo, Seung-moon
• Granted Patent: US 7,522,670 B2
• Time in Patent Office: Days
• US Class Current: 375/257
• CPC Class Codes: H04L 25/0272 Arrangements for coupling to multiple lines, e.g. for differential transmission
• CPC Class Codes: H04L 25/028 Arrangements specific to the transmitter end
• CPC Class Codes: H04L 25/0292 Arrangements specific to the receiver end

Abstract

A digital transmission circuit and method providing selectable power consumption via single-ended or differential operation improves the flexibility of an interface while reducing power consumption when possible. A differential path is provided through the transmitter output driver stages and portions are selectively disabled when the transmission circuit is in a lower-power operating mode. A single-ended to differential converter circuit can be used to construct a differential signal for output to the final driver stage. The selection of power mode can be made via feedback from a channel quality measurement unit or may be hardwired or selected under programmatic control. The longer delay or skew of the lower-power single-ended mode is compensated for by the relaxed requirements of the channel when conditions permit the use of the lower-power single-ended mode.

Claims

1. A transmission circuit for transmitting a digital signal to one or more interface conductors, comprising:

an output driver having a differential input for receiving a differential input signal pair and one or more outputs coupled to said one or more interface conductors;

a pair of pre-driver circuits each having an output coupled to an associated signal of said differential input signal pair; and

a control circuit for selectively disabling power supplied to at least one of said pre-driver circuits in response to a low-power selection state of a control signal, whereby power consumption of said transmission circuit is reduced while transmitting data through said output driver.

2. The transmission circuit of claim 1, wherein said control circuit disables at least a portion of both of said pair of pre-driver circuits in response to said low-power selection state of said control signal, and further comprising a single-ended to differential signal converter having an output coupled to an input of said output driver, and wherein said control circuit disables power supplied to said single-ended to differential signal converter when said control circuit enables said pair of pre-driver circuits in response to a high-power selection state of said control signal.

3. The transmission circuit of claim 2, further comprising a multiplexer having outputs coupled to said inputs of said output driver and inputs coupled to and for selecting between outputs of said single-ended to differential signal converter and said outputs of said pair of pre-driver circuits, and having a select input coupled to said control circuit for performing said selection, whereby said outputs of said single-ended to differential converter are selected for input to said output driver when said control signal is in said low-power selection state and said outputs of said pre-driver circuits are selected for input to said output driver when said control signal is in said high-power selection state.

4. The transmission circuit of claim 3, wherein said control circuit further disables said single-ended to differential converter when said control signal is in said high-power selection state.

5. The transmission circuit of claim 1, further comprising:

a second pair of pre-driver circuits each having an output coupled to an associated signal of said differential input signal pair; and

a control circuit for selectively disabling power supplied to at least one of said second pair of pre-driver circuits in response to said low-power selection state of said control signal.

6. The transmission circuit of claim 1, further comprising:

a first multiplexer for selecting between a pair of input signals and alternatively selecting an input signal from said pair of input signals in conformity with a data clock input, and wherein said first multiplexer has an output coupled to an input of a first one of said pre-driver circuit pair; and

a second multiplexer for selecting between an inverted pair of signals corresponding to said pair of input signals and alternatively selecting an inverted input signal from said inverted pair of signals in conformity with said data clock input, and wherein said second multiplexer has an output coupled to an input of a second one of said pre-driver circuit pair, and wherein said control circuit selectively disables said second multiplexer when said control signal is in said low-power selection state.

7. The transmission circuit of claim 6, further comprising:

at least one buffer circuit having outputs coupled to said first multiplexer for providing said first pair of input signals; and

at least one second buffer circuit having outputs coupled to said first multiplexer for providing said inverted pair of signals, and wherein said control circuit selectively disables said second buffer circuit when said control signal is in said low-power selection state.

8. The transmission circuit of claim 1, further comprising:

a first buffer circuit having an output coupled to an input of a first one of said pre-driver circuit pair; and

a second buffer circuit having an output coupled to an input of a second one of said pre-driver circuit pair, and wherein said control circuit selectively disables said second buffer circuit when said control signal is in said low-power selection state.

9. The transmission circuit of claim 1, wherein said control signal is provided from a programmable register within said transmission circuit.

10. The transmission circuit of claim 1, wherein said control signal is provided from a hard-wired terminal of said transmission circuit.

11. The transmission circuit of claim 1, wherein said output driver has a pair of differential outputs coupled to said one or more interface conductors.

12. The transmission circuit of claim 1, wherein said output driver has a single-ended output coupled to said one of said interface conductors.

13. An interface including:

a transmission circuit for transmitting a digital signal to one or more interface conductors, comprising an output driver having a differential input for receiving a differential input signal pair and one or more outputs coupled to said one or more interface conductors, a pair of pre-driver circuits each having an output coupled to an associated signal of said differential input signal pair, and a control circuit for selectively disabling power supplied to at least one of said pre-driver circuits in response to a low-power selection state of a control signal, whereby power consumption of said transmission circuit is reduced while transmitting data through said output driver; and

an interface quality measurement circuit for providing said control signal in response to a determination of quality of signals on said interface conductors.

14. The interface of claim 13, wherein said interface quality measurement circuit is located on a remote side of said interface conductors opposite said output driver, and further comprising:

a second transmission circuit located on said remote side of said interface and coupled to said interface conductors and said interface quality measurement circuit for transmitting indications of said signal quality determination;

a receiver on a local side of said interface and coupled to said one or more interface conductors for receiving said indications from said remote side of said interface and for providing said control signal in response to said received indications.

15. The interface of claim 13, wherein said interface quality measurement circuit is located on a local side of said interface conductors along with said output driver, and wherein said interface quality measurement circuit is coupled to said control circuit for providing said control signal.

16. A method of controlling power consumption in an digital interface transmitter, comprising:

receiving an indication of that power consumption of said interface transmitter may be reduced; and

disabling one or more internal pre-buffer circuits within said digital interface transmitter and along a first signal of a differential signal path that provides differential input signals to an output driver coupled to interface signal lines in response to said indication.

17. The method of claim 16, further comprising:

measuring a quality of an interface signal on said interface signal lines;

determining whether or not said quality is above a threshold level; and

in response to determining that said quality is above a threshold level, generating said indication.

19. The method of claim 16, wherein said disabling further comprises disabling at least a portion of another set of internal pre-buffer circuits that provides a second signal of said differential signal path, and wherein said method further comprises:

generating an alternative differential signal pair representing said signals of said differential signal path; and

selectively applying said alternative differential signal pair to said output driver in response to said disabling.

20. The method of claim 16, further comprising:

multiplexing two or more information signals onto said differential signal path; and

ceasing multiplexing of at least one of said two or more information signals in response to said disabling.

18. The method of claim 18, wherein said measuring and determining are performed at a remote side of said interface signal lines opposite said interface transmitter and wherein said method further comprises communicating a state of said indication to a receiver at a local side of said interface signal lines whereby said state of said indication is used to perform said disabling at said loal side of said interface.