Low voltage differential signaling driver with programmable on-chip resistor termination

• US 8,008,944 B2
• Filed: 11/25/2008
• Issued: 08/30/2011
• Est. Priority Date: 11/25/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Dixit, Abhay S., Srinivas, Vaishnav
• Primary Examiner(s): Ismail; Shawki S
• Assistant Examiner(s): Tran; Thienvu V
• Application Number:
  US12/323,248
• Publication Number:
  US 20100127736A1
• Time in Patent Office: 1,008 Days
• Field of Search: 326/30
• US Class Current: 326/30
• CPC Class Codes: H03F 2200/78 A comparator being used in a controlling circuit of an amplifier
• CPC Class Codes: H03F 2203/45424 the CMCL comprising a comparator circuit
• CPC Class Codes: H03F 2203/45434 the CMCL output control signal being a voltage signal
• CPC Class Codes: H03F 2203/45641 the LC being controlled, e.g. by a signal derived from a non specified place in the dif amp circuit
• CPC Class Codes: H03F 2203/45642 the LC, and possibly also cascaded stages following it, being (are) controlled by the common mode signal derived to control a dif amp
• CPC Class Codes: H03F 2203/45646 the LC comprising an extra current source
• CPC Class Codes: H03F 2203/45681 the LC comprising offset compensating means
• CPC Class Codes: H03F 2203/45682 the LC comprising one or more op-amps
• CPC Class Codes: H03F 2203/45686 the LC comprising one or more potentiometers, which are not shunting potentiometers
• CPC Class Codes: H03F 2203/45696 the LC comprising more than two resistors
• CPC Class Codes: H03F 2203/45702 the LC comprising two resistors
• CPC Class Codes: H03F 2203/45726 the LC comprising more than one switch, which are not cross coupled
• CPC Class Codes: H03F 3/45179 using MOSFET transistors as the active amplifying circuit H03F3/45278 takes precedence
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/45946 Controlling the loading circuit of the differential amplifier
• CPC Class Codes: H04L 25/0272 Arrangements for coupling to multiple lines, e.g. for differential transmission

Abstract

A low voltage differential signaling driver is disclosed and may include a current steering output circuit having a first driver output and a second driver output. The low voltage differential signaling driver may also include a programmable on-chip resistor.

Claims

1. A low voltage differential signaling driver, comprising:

a current steering output circuit having a first driver output and a second driver output;

a programmable on-chip resistor, wherein the programmable on-chip resistor is selectively operable to act as a termination resistor and control an output swing of the driver by countering a variation in a drive current;

an on-chip reference resistor, substantially similar to the programmable on-chip resistor, driven by a band gap or reference voltage operable to generate a reference bias current; and

a common mode feedback circuit connected to the first driver output and the second driver output, wherein the common mode feedback circuit is operable to selectively control the drive current.

2. The low voltage differential signaling driver of claim 1, wherein the current steering output circuit comprises:

a first positive switch;

a second positive switch;

a first negative switch connected in series with the second positive switch;

a second negative switch connected in series with the first positive switch, wherein the first positive switch and second negative switch are in parallel to the first negative switch and the second positive switch;

a first current source connected to the first positive switch and the second positive switch; and

a second current source connected to the first negative switch and the second negative switch, wherein the first current source and the second current source are derived from the reference bias current and provide the drive current to the low voltage differential signaling driver.

3. The low voltage differential signaling driver of claim 2, wherein the current steering output circuit is operable to switch between a first circuit configuration, wherein the drive current flows through at least the first positive switch, the second driver output, an off-chip termination resistor, the first driver output, and the first negative switch, and a second circuit configuration, wherein the drive current flows through at least the second positive switch, the first driver output, the off-chip termination resistor, the second driver output, and the second negative switch.

4. The low voltage differential signaling driver of claim 2, wherein the first positive switch and the second positive switch comprise p-MOSFET switches and wherein the first negative switch and the second negative switch comprise n-MOSFET switches.

5. The low voltage differential signaling driver of claim 3, further comprising a differential buffer connected to the first positive switch, the second positive switch, the first negative switch, and the second negative switch, wherein the differential buffer is operable to switch the current steering output circuit between the first circuit configuration and the second circuit configuration.

6. The low voltage differential signal driver of claim 1, wherein the common mode feedback circuit is configured to sense a common mode output voltage and compare the common mode output voltage to a reference voltage and the common mode feedback circuit is configured to adjust the drive current of the low voltage differential signal driver at least partially based on the comparison.

7. A device, comprising:

a low voltage differential signaling driver, wherein the low voltage differential signaling driver comprises;

a current steering output circuit having a first driver output and a second driver output;

a programmable on-chip resistor, wherein the programmable on-chip resistor is selectively operable to act as a termination resistor and control an output swing of the driver by countering a variation in a drive current;

an on-chip reference resistor, substantially similar to the programmable on-chip resistor, driven by a band gap or reference voltage operable to generate reference bias current; and

a common mode feedback circuit connected to the first driver output and the second driver output, wherein the common mode feedback circuit is operable to selectively control the drive current.

8. The device of claim 7, wherein the current steering output circuit comprises:

a first positive switch;

a second positive switch;

a first negative switch connected in series with the second positive switch;

a second negative switch connected in series with the first positive switch wherein the first positive switch and second negative switch are in parallel to the first negative switch and the second positive switch;

a first current source connected to the first positive switch and the second positive switch; and

a second current source connected to the first negative switch and the second negative switch, wherein the first current source and the second current source are derived from reference the bias current and provide the drive current to the low voltage differential signaling driver.

9. The device of claim 8, wherein the current steering output circuit is operable to switch between a first circuit configuration, wherein the drive current flows through at least the first positive switch, the second driver output, an on-chip termination resistor, an off-chip termination resistor, the first driver output, and the first negative switch, and a second circuit configuration, wherein the drive current flows through at least the second positive switch, the first driver output, an on-chip termination resistor, the off-chip termination resistor, the second driver output, and the second negative switch.

10. The device of claim 8, wherein the first positive switch and the second positive switch comprise p-MOSFET switches and wherein the first negative switch and the second negative switch comprise n-MOSFET switches.

11. The device of claim 9, further comprising a differential buffer connected to the first positive switch, the second positive switch, the first negative switch, and the second negative switch, wherein the differential buffer is operable to switch the current steering output circuit between the first circuit configuration and the second circuit configuration.

12. The device of claim 7, wherein the common mode feedback circuit is configured to sense a common mode output voltage and compare the common mode output voltage to a reference voltage and the common mode feedback circuit is configured to adjust the drive current of the low voltage differential signal driver at least partially based on the comparison.

13. A device, comprising:

a low voltage differential signaling driver, wherein the low voltage differential signaling driver comprises;

a current steering output means having a first driver output and a second driver output;

a programmable on-chip resistor means, wherein the programmable on-chip resistor means is selectively operable to act as a termination resistor and control an output swing of the driver by countering a variation in a drive current;

an on-chip reference resistor, substantially similar to the programmable on-chip resistor, driven by a band gap or reference voltage operable to generate reference bias current; and

a common mode feedback means connected to the first driver output and the second driver output, wherein the common mode feedback means is operable to selectively control the drive current.

14. The device of claim 13, wherein the current steering output means comprises:

a first positive switch means;

a second positive switch means;

a first negative switch means connected in series with the second positive switch;

a second negative switch means connected in series with the first positive switch means, wherein the first positive switch means and second negative switch means are and in parallel to the first negative switch means and the second positive switch means;

a first current source means connected to the first positive switch means and the second positive switch means; and

a second current source means connected to the first negative switch means and the second negative switch means, wherein the first current source means and the second current source means are derived from the reference bias current and provide the drive current to the low voltage differential signaling driver.

15. The device of claim 14, wherein the current steering output means is operable to switch between a first configuration, wherein a drive current flows through at least the first positive switch means, the second driver output, an off-chip termination resistor, the first driver output, and the first negative switch means, and a second configuration, wherein the drive current flows through at least the second positive switch means, the first driver output, the off-chip termination resistor, the second driver output, and the second negative switch means.

16. The device of claim 14, wherein the first positive switch means and the second positive switch means comprise p-MOSFET switches and wherein the first negative switch means and the second negative switch means comprise n-MOSFET switches.

17. The device of claim 15, further comprising a control means connected to the first positive switch means, the second positive switch means, the first negative switch means, and the second negative switch means, wherein the control means is operable to switch the current steering output means between the first configuration and the second configuration.

18. The device of claim 13, wherein the common mode feedback means is configured to sense a common mode output voltage and compare the common mode output voltage to a reference voltage and the common mode feedback means is configured to adjust the drive current of the low voltage differential signal driver at least partially based on the comparison.

19. A method of converting a complementary metal oxide semiconductor input voltage signal to a differential low voltage signal for off-chip transmission, comprising:

receiving a complementary metal oxide semiconductor input voltage signal at a low voltage differential signaling driver;

converting the complementary metal-oxide semiconductor input voltage signal to a differential output voltage;

switching the low voltage differential signaling driver to a first circuit configuration or a second circuit configuration;

selectively controlling a programmable on-chip resistor on the low voltage differential signaling driver in order to control a driver output swing by countering a variation in a drive current and to provide an on-chip termination resistor;

generating a reference bias current by an on-chip reference resistor, substantially similar to the programmable on-chip resistor, driven by a band gap or reference voltage; and

sensing a common mode output voltage;

comparing the common mode output voltage to the reference voltage; and

adjusting the drive current when the common mode output voltage is not equal to the reference voltage.

20. The method of claim 19, wherein the drive current is adjusted using a common mode feedback circuit.

21. A device, comprising:

means for receiving a complementary metal oxide semiconductor input voltage signal at a low voltage differential signaling driver;

means for converting the complementary metal-oxide semiconductor input voltage signal to a differential output voltage;

means for switching the low voltage differential signaling driver to a first circuit configuration or a second circuit configuration;

means for selectively controlling a programmable on-chip resistor on the low voltage differential signaling driver in order to control a driver output swing by countering a variation in a drive current and to provide an on-chip termination resistor;

means for generating a reference bias current by an on-chip reference resistor, substantially similar to the programmable on-chip resistor, driven by a band gap or reference voltage; and

means for sensing a common mode output voltage;

means for comparing the common mode output voltage to the reference voltage; and

means for adjusting the drive current when the common mode output voltage is not equal to the reference voltage.

22. A device, the device comprising:

logic for receiving a complementary metal oxide semiconductor input voltage signal at a low voltage differential signaling driver;

logic for converting the complementary metal-oxide semiconductor input voltage signal to a differential output voltage,

logic for switching the low voltage differential signaling driver to a first circuit configuration or a second circuit configuration;

logic for selectively controlling a programmable on-chip resistor on the low voltage differential signaling driver in order to control a driver output swing by countering a variation in a drive current and selectively provide an on-chip termination resistor;

logic for generating a reference bias current by an on-chip reference resistor, substantially similar to the programmable on-chip resistor, driven by a band gap or reference voltage; and

logic for sensing a common mode output voltage;

logic for comparing the common mode output voltage to the reference voltage; and

logic for adjusting the drive current when the common mode output voltage is not equal to the reference voltage.