Voltage comparator

Patent metadata

Field	Value
Publication number	US-9685940-B2
Application number	US-201514818114-A
Country	US
Kind code	B2
Filing date	Aug 4, 2015
Priority date	Feb 25, 2015
Publication date	Jun 20, 2017
Grant date	Jun 20, 2017

Abstract

Systems and methods for powering up circuits are described herein. In one embodiment, a method for power up comprises comparing a voltage of a first supply rail with a voltage of a second supply rail, and determining whether the voltage of the first supply rail is within a predetermined amount of the voltage of the second supply rail for at least a predetermined period of time based on the comparison. The method also comprises initiating switching of a plurality of switches coupled between the first and second supply rails upon a determination that the voltage of the first supply rail is within the predetermined amount of the voltage of the second supply rail for at least the predetermined period of time.

First claim

What is claimed is:

1. A power-up system, comprising:
a voltage comparator configured to compare a voltage of a first supply rail with a voltage of a second supply rail, and to output an output signal based on the comparison, wherein the voltage comparator comprises:
a first voltage-controlled oscillator, wherein a frequency of an output signal of the first voltage-controlled oscillator is controlled by the voltage of the first supply rail;
a second voltage-controlled oscillator, wherein a frequency of an output signal of the second voltage-controlled oscillator is controlled by the voltage of the second supply rail;
a first counter configured to count a number of periods of the output signal of the first voltage-controlled oscillator to obtain a first count value;
a second counter configured to count a number of periods of the output signal of the second voltage-controlled oscillator to obtain a second count value; and
a compare circuit configured to generate the output signal of the voltage comparator based on a difference between the first and second count values; and

a controller configured to determine whether the voltage of the first supply rail is within a predetermined amount of the voltage of the second supply rail for at least a predetermined period of time based on the output signal of the voltage comparator, and, upon a determination that the voltage of the first supply rail is within the predetermined amount of the voltage of the second supply rail for at least the predetermined period of time, to initiate switching of a plurality of switches coupled between the first and second supply rails.

2. The system of claim 1 , wherein the first supply rail is an internal supply rail, and the second supply rail is an external supply rail.

3. The system of claim 1 , wherein the output signal of the voltage comparator has a first logic state when the voltage of the first supply rail is within the predetermined amount of the voltage of the second supply rail, and the controller is configured to initiate switching of the plurality of switches when the output signal of the voltage comparator stays at the first logic state for at least the predetermined period of time.

4. The system of claim 1 , wherein the compare circuit is configured to compare the difference with a threshold value, and to generate the output signal of the voltage comparator based on the comparison of the difference with the threshold value.

5. The system of claim 1 , further comprising:
a first synchronous register coupled between the first counter and the compare circuit; and
a second synchronous register coupled between the second counter and the compare circuit, wherein the first and second synchronous registers are configured to synchronously output the first and second count values, respectively, to the compare circuit.

6. The system of claim 5 , further comprising a counter control circuit configured to enable the first counter for a first period of time, and to disable the first counter for a second period of time following the first period of time, wherein the first counter counts the number of periods of the output signal of the first voltage-controller oscillator during the first period of time, and the first synchronous register is configured to read the first count value from the first counter during the second period of time.

7. The system of claim 1 , wherein the voltage comparator comprises:
a voltage divider configured to scale down the voltage of the first supply rail to obtain a first scaled-down voltage, and to scale down the voltage of the second supply rail to obtain a second scaled-down voltage; and
a comparing amplifier configured to compare the first scaled-down voltage with the second scaled-down voltage, and to generate the output signal based on the comparison of the first scaled-down voltage with the second scaled-down voltage.

8. The system of claim 7 , wherein the voltage divider is configured to scale down the voltage of the second supply rail by a larger amount than the voltage of the first supply rail.

9. The system of claim 1 , wherein the controller is configured to initiate switching of the plurality of switches by outputting an acknowledgement signal to a power sequencer, the acknowledgement signal causing the power sequencer to switch on the plurality of switches.

10. The system of claim 9 , wherein the controller is configured to detect a signal from the power sequencer indicating a start of power up, and to enable the voltage comparator in response to the signal from the power sequencer.

11. A power-up system, comprising:
a voltage comparator configured to compare a voltage of a first supply rail with a voltage of a second supply rail, and to output an output signal based on the comparison, wherein the output signal of the voltage comparator has a first logic state when the voltage of the first supply rail is within a predetermined amount of the voltage of the second supply rail;
a controller configured to initiate switching of a plurality of switches coupled between the first and second supply rails when the output signal of the voltage comparator stays at the first logic state for at least a predetermined period of time; and
a counter, wherein the controller is configured to start the counter in response to the output signal of the voltage comparator changing from a second logic state to the first logic state, to reset the counter in response to the output signal of the voltage comparator changing from the first logic state to the second logic state, and to initiate switching of the plurality of switches when a count value of the counter reaches a predetermined count value corresponding to the predetermined period of time.

12. A method for power up, comprising:
converting a voltage of a first supply rail into a first frequency using a first voltage-controlled oscillator controlled by the voltage of the first supply rail;
converting a voltage of a second supply rail into a second frequency using a second voltage-controlled oscillator controlled by the voltage of the second supply rail;
converting the first frequency into a first count value using a first counter;
converting the second frequency into a second count value using a second counter;
determining a count difference between the first and second count values;
determining whether the voltage of the first supply rail is within a predetermined amount of the voltage of the second supply rail for at least a predetermined period of time based on the count difference; and
initiating switching of a plurality of switches coupled between the first and second supply rails upon a determination that the voltage of the first supply rail is within the predetermined amount of the voltage of the second supply rail for at least the predetermined period of time.

13. The method of claim 12 , wherein the first supply rail is an internal supply rail, and the second supply rail is an external supply rail.

14. The method of claim 12 , wherein determining whether the voltage of the first supply rail is within the predetermined amount of the voltage of the second supply rail for at least the predetermined period of time comprises determining that the voltage of the first supply rail is within the predetermined amount of the voltage of the second supply rail for at least the predetermined period of time when the count difference is below a threshold for at least the predetermined period of time.

15. A method for power up, comprising:
comparing a voltage of a first supply rail with a voltage of a second supply rail;
determining whether the voltage of the first

Assignees

• Qualcomm Inc

Inventors

• Vilangudipitchai Ramaprasath
• Kumar Dorav
• Dillen Steven James
• Kwon Ohsang
• Jaffari Javid

Classifications

• H03K5/26

  the characteristic being duration, interval, position, frequency, or sequence · CPC title

• H03K19/0016

  by using a control or a clock signal, e.g. in order to apply power supply · CPC title

• H03K5/24 Primary

  the characteristic being amplitude · CPC title

• H03K17/04206 Primary

  in field-effect transistor switches · CPC title