Methods and systems for providing load-adaptive output current drive

• US 6,859,069 B2
• Filed: 11/12/2003
• Issued: 02/22/2005
• Est. Priority Date: 02/21/2002
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Ajit, Janardhanan S.
• Primary Examiner(s): Chang, Daniel D.
• Application Number:
  US10/704,901
• Publication Number:
  US 20040155683A1
• Time in Patent Office: 468 Days
• Field of Search: 326/87, 326/27, 326/83, 326/26, 326/34, 327/332, 327/381
• US Class Current: 326/87
• CPC Class Codes: H03K 17/167 using parallel switching arrangements
• CPC Class Codes: H03K 19/00361 in field effect transistor circuits
• CPC Class Codes: H03K 19/018521 of complementary type, e.g. CMOS

Abstract

Methods and systems for sensing load conditions and for adjusting output current drive according to the sensed load conditions to maintain one or more signal characteristics within a desired range. Load conditions are sensed by monitoring one or more signal characteristics that are affected by load conditions, such as voltage changes with respect to time. Output current drive is then adjusted, as needed, to maintain the one or more desired signal characteristics. In an embodiment, rising and/or falling edge slopes are monitored. For example, a dV/dt may be monitored. The dV/dt can be monitored by coupling a capacitance to the output signal, generating a current with the capacitance, and generating a voltage from the current. The voltage is generally proportional to the dV/dt. Depending upon the load conditions, a supplemental current is generated and/or adjusted and added to the output signal to maintain the desired signal characteristics within a desired range. For example, where dV/dt is monitored, the supplemental current is generated and/or adjusted to maintain the dV/dt within a desired range. In this way, the desired signal characteristic(s) are substantially maintained within the desired range for a range of load values. One or more signal characteristics may be maintained over a load range of 50 pF to 600 pF. Signal characteristics may be sensed and maintained only during rising and falling edges. Signal characteristics may be separately sensed and maintained for rising and falling edges of data signals.

Claims

1. A method for providing load-adaptive output current drive, comprising:

sensing load conditions by generating a sensor signal having a voltage substantially proportional to one or more signal characteristics of a signal at an output node coupled to a load, said one or more signal characteristics being affected by said load conditions;

generating a supplemental drive current according to said voltage to maintain said one or more signal characteristics within a desired range; and

combining said supplemental drive current with a primary output current to provide a compensated output signal to said output node;

whereby said one or more signal characteristics of said compensated output signal are substantially maintained within said desired range over a range of said load conditions.

2. The method according to claim 1, wherein said load conditions include variations in load impedance from about 50 pF to about 600 pF.

3. The method according to claim 1, wherein said sensing load conditions and said generating a supplemental drive current are performed during rising edges and falling edges of said signal at said output node.

4. A method for providing a load-adaptive output current drive, comprising:

sensing a change in voltage with respect to time (“

dV/dt”

) of an output signal provided to a load at an output node by generating a sensor signal having a voltage substantially proportional to said dV/dt;

generating a supplemental drive current;

reducing said supplemental drive current when said voltage increases until said sensed dV/dt is within a desired range for a range of load values;

increasing said supplemental drive current when said voltage decreases until said sensed dV/dt is within said desired range for said range of load values; and

combining said supplemental drive current with a primary output current.

5. The method according to claim 4, wherein said range of load values is from about 50 pF to about 600 pF.

6. The method according to claim 4, wherein said sensing a dV/dt of an output signal and said generating a supplemental drive current are performed during rising edges and falling edges of said output signal.

7. The method according to claim 4, wherein said step of sensing a dV/dt further comprises:

coupling a capacitance to said output node;

generating a current with said capacitance; and

generating said voltage from said current that is substantially proportional to said dV/dt.

8. The method according to claim 7, wherein said capacitance comprises one or more discrete capacitors.

9. The method according to claim 7, wherein said capacitance comprises one or more PMOS transistors configured as capacitors.

10. A load-adaptive output current driver, comprising:

a primary output current driver that generates a primary output current in response to a received signal;

a load sensor coupled to an output node, said load sensor generating a sensor signal having a voltage substantially proportional to one or more signal characteristics at said output node, said one or more signal characteristics being affected by load conditions at said output node;

a supplemental output driver coupled to receive said sensor signal, said supplemental output driver controller generating a supplemental drive current in response to said voltage to maintain said one or more signal characteristics within a desired range for a range of said load conditions; and

a summing node coupled to receive said primary output current and said supplemental drive current, said summing node combines said primary output current and said supplemental drive current to provide a compensated output signal to said output node.

11. The load-adaptive current driver according to claim 10, wherein said load conditions include variations in load impedance from about 50 pF to about 600 pF.

12. The load-adaptive current driver according to claim 10, wherein said primary output driver, said load sensor, and said supplemental output driver include rising edge portions and falling edge portions to separately maintain said one or more signal characteristics for rising and falling edges of said received signal.

13. The load-adaptive current driver according to claim 10, comprising:

a plurality of load sensors; and

a plurality of supplemental output drivers configured to generate additional supplemental drive current in order to maintain said one or more signal characteristics within said desired range for said range of said load conditions.