Low power small area oscillator-based ADC

Patent metadata

Field	Value
Publication number	US-9903892-B2
Application number	US-201414480321-A
Country	US
Kind code	B2
Filing date	Sep 8, 2014
Priority date	Sep 8, 2014
Publication date	Feb 27, 2018
Grant date	Feb 27, 2018

Abstract

In one embodiment, a method for measuring current comprises generating a sensor current based on a current being measured. The method also comprises converting a combined current into a first frequency, wherein the combined current is a sum of the sensor current and a common-mode current, and converting the first frequency into a first count value. The method further comprises converting the common-mode current into a second frequency, converting the second frequency into a second count value, and subtracting the second count value from the first count value to obtain a current reading.

First claim

What is claimed is:

1. A method for measuring current, comprising:
generating a sensor current based on a current being measured;
converting a combined current into a first frequency using a first current-controlled oscillator, wherein the combined current is a sum of the sensor current and a common-mode current;
converting the first frequency into a first count value;
converting the common-mode current into a second frequency using the first current-controller oscillator or a second current-controlled oscillator;
converting the second frequency into a second count value; and
subtracting the second count value from the first count value to obtain a current reading.

2. The method of claim 1 , wherein the sensor current is approximately proportional to the current being measured.

3. The method of claim 2 , wherein the current being measured flows through a first transistor, and wherein generating the sensor current comprises mirroring the current flowing through the first transistor using a second transistor having a gate coupled to a gate of the first transistor.

4. The method of claim 3 , wherein the first transistor has a channel width that is at least ten times greater than a channel width of the second transistor.

5. The method of claim 1 , wherein converting the first frequency into the first count value comprises counting a number of cycles of the first current-controlled oscillator over a first period of time, and converting the second frequency into the second count value comprises counting a number of cycles of the second current-controlled oscillator over a second period of time.

6. The method of claim 5 , wherein the first period of time and the second period of time are approximately the same.

7. The method of claim 1 , wherein the first current-controlled oscillator comprises a first plurality of inverters coupled into a loop, and the second current-controlled oscillator comprises a second plurality of inverters coupled into a loop.

8. The method of claim 1 , wherein converting the combined current into the first frequency comprises converting the combined current into the first frequency using the first current-controlled oscillator during a first period of time, converting the common-mode current into the second frequency comprises converting the common-mode current into the second frequency using the first current-controlled oscillator during a second period of time, and the first period of time and the second period of time are non-overlapping.

9. The method of claim 8 , wherein converting the first frequency into the first count value comprises counting a number of cycles of the first current-controlled oscillator over the first period of time, and converting the second frequency into the second count value comprises counting a number of cycles of the first current-controlled oscillator over the second period of time.

10. The method of claim 1 , wherein the common-mode current is approximately constant.

11. The method of claim 1 , wherein a dynamic range of the sensor current is at least ten times greater than a dynamic range of the combined current, the dynamic range of the sensor current is defined by a ratio of a first sensor current value over a second sensor current value, and the dynamic range of the combined current is defined by a ratio of a sum of a common-mode current value and the first sensor current value over a sum of the common-mode current value and the second sensor current value.

12. The method of claim 1 , wherein the sensor current is generated by mirroring a current supplied from a power-supply rail to a circuit through a power switch.

13. The method of claim 12 , wherein the circuit comprises a processor core.

14. Apparatus for measuring current, comprising:
means for generating a sensor current based on a current being measured;
means for converting a combined current into a first frequency, wherein the combined current is a sum of the sensor current and a common-mode current;
means for converting the first frequency into a first count value;
means for converting the common-mode current into a second frequency;
means for converting the second frequency into a second count value; and
means for subtracting the second count value from the first count value to obtain a current reading.

15. The apparatus of claim 14 , wherein the sensor current is approximately proportional to the current being measured.

16. The method of claim 14 , wherein the common-mode current is approximately constant.

17. The apparatus of claim 14 , wherein a dynamic range of the sensor current is at least ten times greater than a dynamic range of the combined current, the dynamic range of the sensor current is defined by a ratio of a first sensor current value over a second sensor current value, and the dynamic range of the combined current is defined by a ratio of a sum of a common-mode current value and the first sensor current value over a sum of the common-mode current value and the second sensor current value.

18. A current sensor, comprising:
a sensor circuit configured to generate a sensor current based on a current being measured;
a first current-controlled oscillator configured to convert a combined current into a first frequency, wherein the combined current is a sum of the sensor current and a common-mode current;
a first counter configured to convert the first frequency into a first count value;
a second current-controlled oscillator configured to convert the common-mode current into a second frequency;
a second counter configured to convert the second frequency into a second count value; and
a subtractor configured to subtract the second count value from the first count value to obtain a current reading.

19. The current sensor of claim 18 , wherein the sensor current is approximately proportional to the current being measured.

20. The current sensor of claim 19 , wherein the current being measured flows through a first transistor, the sensor circuit comprises a second transistor having a gate coupled to a gate of the first transistor, and the second transistor is configured to mirror the current flowing through the first transistor.

21. The current sensor of claim 18 , wherein the first current-controlled oscillator comprises a first plurality of inverters coupled into a loop, and the second current-controlled oscillator comprises a second plurality of inverters coupled into a loop.

22. The method of claim 18 , wherein the common-mode current is approximately constant.

23. A current sensor, comprising:
a sensor circuit configured to generate a sensor current based on a current being measured;
a current-controlled oscillator coupled to a common-mode current;
a switch configured to selectively couple the sensor current to the current-controlled oscillator;
a controller configured to close the switch during a first period of time and to open the switch during a second period of time, wherein the current-controlled oscillator is configured to convert a combined current into a first frequency during the first period of time, the combined current being a sum of the sensor current and the common-mode current, and to convert the common-mode current into a second frequency during the second period of time;
a counter configured to convert the first frequency into a first count value and to convert the second frequency into a second count value; and
a subtractor circuit configured to subtract the second count value from the f

Assignees

• Qualcomm Inc

Inventors

• Zhang Chuang
• Chen Nan
• Zhang Junmou

Classifications

• H03M1/1295

  Clamping, i.e. adjusting the DC level of the input signal to a predetermined value · CPC title

• H03M1/0607 Primary

  Offset or drift compensation (removal of offset already present on the analogue input signal H03M1/1295) · CPC title

• G01R23/10

  by converting frequency into a train of pulses, which are then counted {, i.e. converting the signal into a square wave} · CPC title

• G01R19/252 Primary

  using analogue/digital converters of the type with conversion of voltage or current into frequency and measuring of this frequency · CPC title

• H03M1/60

  with intermediate conversion to frequency of pulses · CPC title