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 Title: |
US6184730:
CMOS output buffer with negative feedback dynamic-drive control and dual P,N active-termination transmission gates
[ Derwent Title ]
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| Country: |
US United States of America
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| Inventor: |
Kwong, David; Fremont, CA
Chen, Baohua; Mountain View, CA
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| Assignee: |
Pericom Semiconductor Corp., San Jose, CA
other patents from PERICOM SEMICONDUCTOR CORP. (713978) (approx. 58)
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| Published / Filed: |
2001-02-06
/ 1999-11-03
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| Application Number: |
US1999000432368
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| IPC Code: |
Advanced:
H03K 17/16;
H03K 19/003;
Core:
more...
IPC-7:
H03B 1/00;
H03K 3/00;
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| U.S. Class: |
Current:
327/112;
327/389;
Original:
327/112;
327/389;
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| Field of Search: |
327/108,109,111,112,379,389,427,434,437
326/082,83,85,87,27
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| Priority Number: |
| 1999-11-03 |
US1999000432368 |
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| Abstract: |
An output buffer for a line driver uses transmission gates for active termination. A large p-channel driver is pulsed on during a low-to-high output transition, but this driver is turned off once the output voltage reaches a threshold. A feedback circuit includes a sensing inverter that has its input connected to the output node. The sensing inverter causes the gate of the p-channel driver to be driven high once the output swings past the threshold. A similar n-channel driver transistor is pulsed on during a low-going output transition but is disabled by a feedback circuit that senses the output voltage falling below a threshold. A pullup transmission gate is also connected between the output and the power supply, while a pulldown transmission gate is connected between the output and ground. Each transmission gate contains a p-channel and a n-channel transistor in parallel. The sizes of the p-channel and n-channel transistors in the transmission gate is sufficiently small to provide a resistance of 25 to 30 ohms. Both transistors in the pullup transmission gate are turned on when the output is driven high, while both transistors of the pulldown transmission gate are turned on when the output is driven low. Having both n and p transistors of the transmission gate on provides a more linear resistance across the voltage swing of the output. Since termination of about 25-30 ohms is provided by the transmission gate, an external series resistor is not needed for dampening. When driving large capacitive loads, several nanoseconds of R-C delay can be saved.
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| Attorney, Agent or Firm: |
Auvinen, Stuart T. ;
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| Primary / Asst. Examiners: |
Ton, My-Trang Nu;
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| INPADOC Legal Status: |
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| Family: |
None
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First Claim:
Show all 20 claims |
We claim:
1. A high-drive output buffer with active termination comprising:
- an output pad for connecting to an external output load;
- a pullup driver transistor, coupled to strongly drive the output pad to a higher voltage during a rising transition of the output pad, the pullup driver transistor being controlled by a pullup gate;
- a pulldown driver transistor, coupled to strongly drive the output pad to a lower voltage during a falling transition of the output pad, the pulldown driver transistor being controlled by a pulldown gate;
- a sensor, coupled to the output pad, for detecting when the output pad has been driven to a threshold voltage, the sensor disabling the pullup driver transistor near an end of the rising transition, the sensor disabling the pulldown driver transistor near an end of the falling transition;
- a pullup transmission gate, coupled to the output pad, for providing a terminating impedance to the output pad after the end of the rising transition after sensor has disabled the pullup driver transistor, the pullup transmission gate also for weakly driving the output pad to a higher voltage during the rising transition; and
- a pulldown transmission gate, coupled to the output pad, for providing a terminating impedance to the output pad after the end of the falling transition after sensor has disabled the pulldown driver transistor, the pulldown transmission gate also for weakly driving the output pad to a lower voltage during the falling transition,
- whereby the output pad is terminated by the pullup transmission gate after the rising transition, but terminated by the pulldown transmission gate after the falling transition.
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| Background / Summary: |
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| Drawing Descriptions: |
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| Description: |
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| Forward References: |
Show 18 U.S. patent(s) that reference this one
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