Programmable differential signaling system

• US 7,265,586 B1
• Filed: 02/25/2005
• Issued: 09/04/2007
• Est. Priority Date: 02/25/2005
• Status: Active Grant

• Current Assignee: Xilinx, Inc. (Advanced Micro Devices, Inc.)
• Original Assignee: Xilinx, Inc. (Advanced Micro Devices, Inc.)
• Inventors: Cline, Ronald L., Huang, Gubo, Zhou, Shi-dong, Nguyen, Andy T.
• Primary Examiner(s): LE, DON P
• Application Number:
  US11/067,422
• Time in Patent Office: 921 Days
• Field of Search: 326 37- 41, 326 83- 86
• US Class Current: 326/83
• CPC Class Codes: H04L 25/0264 Arrangements for coupling to transmission lines duplexing arrangements H04L5/14; line equalisers, line build-out devices H04L25/03878
• 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 25/0288 the shape being matched to the transmission line pre-equalisation per se H04L25/03343

Abstract

A programmable differential signaling system includes a programmable bias generator and a plurality of input/output modules. The programmable bias generator is operably coupled to generate a first global bias signal and a second global signal based on desired signal properties of one of a plurality of differential signaling conventions. The a plurality of input/output modules is operably coupled to convert between differential signaling and single ended signaling, wherein actual signal properties of the differential signaling are regulated based on the first and second global bias signals to substantially equal the desired signal properties.

Claims

1. A programmable differential signaling system comprises:

programmable bias generator operably coupled to generate a first global bias signal and a second global signal based on desired signal properties of one of a plurality of differential signaling conventions;

a plurality of input/output modules operably coupled to convert between differential signaling and single ended signaling, wherein actual signal properties of the differential signaling are regulated based on the first and second global bias signals to substantially equal the desired signal properties; and

wherein an input/output module of the plurality of input/output modules comprises;

a low voltage shifter operably coupled to shift a voltage level of a single-ended signal;

a pre-driver circuit operably coupled to convert between the signal-ended signal and low voltage differential signal (LVDS) drive signals; and

a low voltage differential signal (LVDS) driver operably coupled to convert between the LVDS drive signals and a differential signal, wherein signal properties of the differential signal is in accordance with the desired signal properties.

2. The programmable differential signaling system of claim 1, wherein the LVDS driver comprises:

a first LVDS node;

a second LVDS node;

a load impedance circuit operably coupled between the first and second LVDS nodes; and

a switching circuit operably coupled to provide the differential signal at the first and second LVDS nodes in accordance with LVDS drive signals, wherein the switching circuit includes a plurality of current controlled switching transistor circuits.

3. The programmable differential signaling system of claim 2, wherein each of the plurality of controlled switching transistor circuits comprises:

a cascode transistor having an input operably coupled to receive a bias control signal; and

a switching transistor coupled in series with the cascode transistor, wherein an input of the switching transistor is operably coupled to receive a switching signal in accordance with the input signal.

4. The programmable differential signaling system of claim 3, wherein the LVDS driver further comprises:

a first operational amplifier having a first input, a second input, and an output, wherein the first input of the first operational amplifier is operably coupled to receive the first global biasing signal, the second input of the first operational amplifier is operably coupled to receive a coupling node of the cascode transistor to the switching transistor, and the output of the first operational amplifier provides the bias control signal to a first pairing of the cascode transistor and the switching transistor; and

a second operational amplifier having a first input, a second input, and an output, wherein the first input of the second operational amplifier is operably coupled to receive the second global biasing signal, the second input of the second operational amplifier is operably coupled to receive a coupling node of the cascode transistor to the switching transistor, and the output of the second operational amplifier provides the bias control signal to a second pairing of the cascode transistor and the switching transistor.

5. The programmable differential signaling system of claim 4, wherein the LVDS driver further comprises:

a first multiplexer operably coupled to provide the output of the first operational amplifier as the bias control signal to the first pairing of the cascode transistor and the switching transistor when a differential enable signal is active and to provide power supply rail voltage as the bias control signal to the first pairing of the cascode transistor and the switching transistor when the differential enable signal is inactive; and

a second multiplexer operably coupled to provide the output of the second operational amplifier as the bias control signal to the second pairing of the cascode transistor and the switching transistor when the differential enable signal is active and to provide a ground rail voltage as the bias control signal to the second pairing of the cascode transistor and the switching transistor when the differential enable signal is inactive.

6. The programmable differential signaling system of claim 2, wherein the plurality of current controlled switching transistor circuits comprises:

a first switching transistor, wherein an input of the first switching transistor is operably coupled to receive a first switching signal in accordance with the input signal and wherein a second node of the first switching transistor is operably coupled to the first node of the LVDS driver;

a second switching transistor, wherein an input of the second switching transistor is operably coupled to receive a second switching signal in accordance with the input signal, wherein a second node of the second switching transistor is operably coupled to the second node of the LVDS driver;

a third switching transistor, wherein an input of the third switching transistor is operably coupled to receive a first switching signal in accordance with the input signal, wherein a first node of the third switching transistor is operably coupled to the first node of the LVDS driver;

a fourth switching transistor, wherein an input of the fourth switching transistor is operably coupled to receive a second switching signal in accordance with the input signal, wherein a first node of the fourth switching transistor is operably coupled to the second node of the LVDS driver;

a first cascode transistor, wherein an input of the first cascode transistor is operably coupled to receive a first biasing signal, wherein a first node of the first cascode transistor is coupled to a power supply rail and a second node of the first cascode transistor is coupled to a first node of each of the first and second switching transistors; and

a second cascode transistor, wherein an input of the second cascode transistor is operably coupled to receive a second biasing signal, wherein a second node of the first cascode transistor is coupled to a ground rail and a first node of the second cascode transistor is coupled to a second node of each of the third and fourth switching transistors.

7. The programmable differential signaling system of claim 2, wherein the programmable bias generator comprises:

a first programmable biasing module operably coupled to produce the first global bias signal such that, respectively, differential voltage and common-mode voltage of the differential signaling substantially equal desired differential voltage and desired common-mode voltage of the desired signal properties; and

a second programmable biasing module operably coupled to provide the second global bias signal such that the common-mode voltage of the differential signaling substantially equals the desired common-mode voltage.

8. The programmable differential signaling system of claim 7, wherein the first programmable biasing module comprises:

a current mirroring circuit operably coupled to mirror current within at least a representative one of the current controlled switching transistor circuits of the LVDS driver; and

an operational amplifier to establish a bias voltage for the current mirroring circuit based on the desired differential voltage, the desired common-mode voltage, and the common mode voltage.

9. The programmable differential signaling system of claim 8, wherein the current mirroring circuit comprises:

a current mirror transistor, wherein an input of the current mirror transistor is operably coupled to an output of the operational amplifier;

an adjustable resistive network operably coupled to the current mirror transistor, wherein the adjustable resistive network provides an impedance based on a control signal wherein; and

control module operably coupled to produce the control signal such that the impedance and current of the current mirror transistor correspond to the desired differential voltage and the desired common-mode voltage.

10. The programmable differential signaling system of claim 7, wherein the second programmable biasing module comprises:

an operational amplifier to establish the second global bias signal based on the desired common-mode voltage and the common mode voltage.