LEVEL SHIFTER AND METHOD OF CALIBRATION

• US 20170288672A1
• Filed: 03/20/2017
• Published: 10/05/2017
• Est. Priority Date: 03/30/2016
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Schemm, Nathan Richard
• Granted Patent: US 10,097,183 B2
• Time in Patent Office: Days
• CPC Class Codes: H03K 19/018507 Interface arrangements

Abstract

A level shifter includes a signal generator that generates differential signals on a first output and a second output. A first capacitor is coupled between the first output and a first node and a second capacitor is coupled between the second output and a second node. A third capacitor is coupled between the first node and a first voltage potential, wherein the capacitance of the third capacitor is variable. A fourth capacitor is coupled between the second node and the first voltage potential, wherein the capacitance of the fourth capacitor is variable.

Claims

1. A level shifter comprising:

a signal generator generating differential signals on a first output and a second output;

a first capacitor coupled between the first output and a first node;

a second capacitor coupled between the second output and a second node;

a third capacitor coupled between the first node and a first voltage potential, wherein the capacitance of the third capacitor is variable; and

a fourth capacitor coupled between the second node and the first voltage potential, wherein the capacitance of the fourth capacitor is variable.

2. The level shifter of claim 1, further comprising a voltage potential selectively coupled to the first node and selectively coupled to the second node.

3. The level shifter of claim 2, further comprising a first differential amplifier having inputs coupled to the first node and the second node, the output of the first differential amplifier being coupled to the output of the level shifter, wherein the voltage potential is the common mode voltage of the first differential amplifier.

4. The level shifter of claim 1, further comprising a second differential amplifier having a first input coupled to the first node and a second input coupled to the second node, wherein the capacitance values of at least one of the third capacitor and the fourth capacitor are set in response to the output of the second differential amplifier.

5. The level shifter of claim 4, further comprising a processor coupled to the output of the second differential amplifier, the processor providing instructions to set the capacitance values of the third and fourth capacitor in response to a signal output by the second differential amplifier.

6. The level shifter of claim 5, wherein the processor couples and decouples a voltage potential to the first node and the second node.

7. The level shifter of claim 6, wherein the processor measures the common mode transient immunity between the first node and the second node after a cycle of coupling the second voltage potential to the first node and the second node followed by decoupling the second voltage potential from the first node and the second node.

8. The level shifter of claim 1, further comprising at least one comparator coupled to the output of the level shifter.

9. The level shifter of claim 8, wherein amplitudes of signals generated by the signal generator are variable and wherein threshold levels of the at least one comparator are set in response to the amplitudes of signals generated by the signal generator.

10. A method of calibrating a level shifter, the method comprising:

coupling a first node to a first voltage potential, the first node being coupled to a first capacitor coupled to a signal generator, a second capacitor coupled to a second voltage potential, and a first input to a first differential amplifier;

coupling a second node to the first voltage potential, the second node being coupled to a third capacitor coupled to the signal generator, a fourth capacitor coupled to the second voltage potential, and a second input to the first differential amplifier;

decoupling the first voltage from the first node and the second node;

sweeping a voltage across the level shifter to generate a differential voltage between the first node and the second node;

measuring the voltage difference between the first node and the second node; and

adjusting the capacitance value of at least one of the second capacitor and the fourth capacitor in response to the measuring.

11. The method of claim 10, wherein inputs of a second differential amplifier are coupled to the first node and the second node, and wherein the measuring comprises measuring the output voltage of the second differential amplifier.

12. The method of claim 10, wherein the adjusting comprises adjusting the capacitance value of at least one of the second capacitor and the fourth capacitor to equalize the voltages between the first node and the second node.

13. The method of claim 12, wherein equalizing the voltages on the first node and the second node comprises making the voltage on the first node within a predetermined value of the voltage on the second node.

14. The method of claim 10, wherein the first voltage potential is a function of the common-mode rejection ratio of the first differential amplifier.

15. The method of claim 10, further wherein adjusting the capacitance value of at least one of the second capacitor and the fourth capacitor in response to the measuring indicating that the voltage difference between the first node and the second node exceeds a predetermined value.

16. A method of calibrating a level shifter, the method comprising:

generating a signal, the signal being a control signal for the level shifter, the signal having an amplitude less that the control signal used during operation of the level shifter;

transmitting the signal through a capacitive voltage divider;

transmitting the signal into a comparator; and

adjusting the threshold of the comparator to where the signal is detected above a noise margin.

17. The method of claim 16, wherein generating a signal comprises generating a signal having half the amplitude of the control signal used during operation of the level shifter.

18. The method of claim 16, wherein generating a signal comprises generating a differential signal.

19. The method of claim 16 further comprising transmitting the signal through at least one differential amplifier coupled between the voltage divider and the comparator.