High speed IO buffer

• US 20080079457A1
• Filed: 09/29/2006
• Published: 04/03/2008
• Est. Priority Date: 09/29/2006
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Yuan, Jao Che
• Granted Patent: US 7,446,558 B2
• Time in Patent Office: Days
• US Class Current: 326/30
• CPC Class Codes: H03K 19/0005 Modifications of input or output impedance
• CPC Class Codes: H03K 19/018592 with a bidirectional operation
• CPC Class Codes: H04L 25/0278 Arrangements for impedance matching
• CPC Class Codes: H04L 5/1461 Suppression of signals in the return path, i.e. bidirectional control circuits

Abstract

A bi-directional buffer is provided. The buffer includes a driver, a receiver, and a circuitry configured to select a driving mode in response to detecting a first condition and to select a receiving mode in response to detecting a second condition. The driving mode has a first impedance and the receiving mode has a second impedance. The second impedance is partially contributed from the driver.

Claims

1. An IO buffer for driving and receiving operations, the buffer comprising:

a driver, comprising;

a first switch;

a first resistive element serially coupled to the first switch;

a second resistive element coupled to the first resistive element via an output node; and

a second switch serially coupled to the second resistive element; and

a receiver, comprising;

a third switch;

a third resistive element serially coupled to the third switch;

a fourth resistive element coupled to the third resistive element via the output node; and

a fourth switch serially coupled to the fourth resistive element;

wherein in a receiving mode, at least one of the first and the second switches is turned on.

2. The buffer of claim 1, wherein the first switch, the second switch, the third switch, and the fourth switch respectively comprise at least one transistor.

3. The buffer of claim 2, wherein the transistor is selectively a NMOS or a PMOS.

4. The buffer of claim 1, wherein in a driving mode, if a data with a high logic value is to be outputted at said output node, the first switch and the third switch are turned on, and the second switch and the fourth switch are turned off.

5. The buffer of claim 1, wherein in a driving mode, if a data with a low logic value is to be outputted at said output node, the first switch and the third switch are turned off, and the second switch and the fourth switch are turned on.

6. The buffer of claim 1, wherein in the receiving mode, the first, second, third, and fourth switches are all turned on.

7. The buffer of claim 1, wherein the driver further comprises:

a programmable driving array, comprising;

N fifth switches, wherein N is a positive integer;

N fifth resistive elements, each of the fifth resistive elements being serially coupled to one of the N fifth switches, respectively;

N sixth resistive elements, each of the sixth resistive elements being coupled to one of the N fifth resistive elements via said output node, respectively; and

N sixth switches, each of the sixth switches being serially coupled to one of the N sixth resistive elements;

wherein in a driving mode, the N fifth switches and the N sixth switches are programmed to be selectively turned on.

8. The buffer of claim 1, wherein the receiver further comprises:

a programmable receiving array, comprising;

M seventh switches, wherein M is a positive integer;

M seventh resistive elements, each of the seventh resistive elements being serially coupled to one of the M seventh switches, respectively;

M eighth resistive elements, each of the eighth resistive elements being coupled to one of the M seventh resistive elements via said output node, respectively; and

M eighth switches, each of the eighth switches being serially coupled to one of the M eighth resistive elements;

wherein in the receiving mode, the M seventh switches and the M eighth switches are programmed to be selectively turned on.

9. A bi-directional buffer comprising:

a driver;

a receiver; and

a circuitry configured to;

select a driving mode in response to detecting a first condition, wherein the driving mode has a first impedance; and

select a receiving mode in response to detecting a second condition, wherein the receiving mode has a second impedance and the second impedance is partially contributed from the driver.

10. The buffer of claim 9, wherein the driver comprises:

a programmable driving array, comprising;

N first switches, wherein N is a positive integer;

N first resistive elements, each of the first resistive elements being serially coupled to one of the N first switches, respectively;

N second resistive elements, each of the second resistive elements being coupled to one of the N first resistive elements via an output node, respectively; and

N second switches, each of the second switches being serially coupled to one of the N second resistive elements;

wherein in the receiving mode, the N first switches and the N second switches are programmed to be selectively turned on to form a first part of the second impedance.

11. The buffer of claim 9, wherein the receiver comprises:

a programmable receiving array, comprising;

M third switches, wherein M is a positive integer;

M third resistive elements, each of the third resistive elements being serially coupled to one of the M third switches, respectively;

M fourth resistive elements, each of the fourth resistive elements being coupled to one of the M third resistive elements via an output node, respectively; and

M fourth switches, each of the fourth switches being serially coupled to one of the M fourth resistive elements;

wherein in the receiving mode, the M third switches and the M fourth switches are programmed to be selectively turned on to form a second part of the second impedance.