Methods, sub-systems and systems that reduce a mismatch error associated with an analog circuit

• US 8,847,139 B2
• Filed: 08/16/2011
• Issued: 09/30/2014
• Est. Priority Date: 08/24/2010
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Dyer, Kenneth C.
• Primary Examiner(s): Le, Que T
• Assistant Examiner(s): BENNETT, JENNIFER D
• Application Number:
  US13/211,237
• Publication Number:
  US 20120049927A1
• Time in Patent Office: 1,141 Days
• Field of Search: 250/214.AL, 250/214.1, 250/214.R, 250/205, 250/214.A, 250/214.B, 250/338.1, 250/339.02, 250/214.C, 250/214.DC, 250/221, 340/540, 340/555, 340/600, 340/870.21, 340/146.2, 345/207, 356/350, 348/602, 348/603, 330/257, 330/258, 327/53, 327/66, 327/490, 327/514, 341/135, 341/133
• US Class Current: 250/214.R
• CPC Class Codes: G05F 3/262 using field-effect transistors only
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

Circuits, methods, sub-systems and systems including adaptive analog subtraction for light sensing are described herein. In an embodiment, an analog circuit including a current mirror is configured to replicate a first current to produce a replicated version of the first current, and to subtract the replicated version of the first current from a second current to produce a third current. A mismatch correction circuit is configured to produce an adjustment signal, indicative of a mismatch error associated with the analog circuit, based on a digital version of the third current. This adjustment signal is used to reduce the mismatch error associated with the analog circuit.

Claims

1. A sub-system, comprising:

an analog circuit configured to replicate a first current to produce a replicated version of the first current, and to subtract the replicated version of the first current from a second current to produce a third current; and

a mismatch correction circuit configured to produce an adjustment signal, indicative of a mismatch error associated with the analog circuit, based on a digital version of the third current;

wherein the adjustment signal is used to reduce the mismatch error associated with the analog circuit.

2. The sub-system of claim 1, wherein:

the analog circuit comprises a current mirror that is configured to replicate the first current to produce the replicated version of the first current; and

the mismatch correction circuit comprises circuitry configured to adjust a gain of the current mirror to thereby reduce the mismatch error associated with the analog circuit.

3. The sub-system of claim 2, wherein the mismatch correction circuit is configured to selectively adjust the gain of the current mirror by selectively connecting and/or disconnecting one or more transistors within the current mirror circuit.

4. The sub-system of claim 2, wherein the mismatch correction circuit is configured to selectively adjust the gain of the current mirror by adjusting one or more voltages within the current mirror.

5. The sub-system of claim 2, wherein:

the current mirror includes a chopper circuit that is driven by a chopper signal; and

the mismatch correction circuit includes

a digital amplitude demodulator configured to demodulate the digital version of the third current, using the chopper signal or a reproduced or recovered version of the chopper signal, to thereby produce a digital demodulation output; and

a digital filter configured to filter the digital demodulation output to thereby produce the adjustment signal.

6. The sub-system of claim 5, further comprising:

an analog-to-digital converter (ADC) configured to receive the third current and to output the digital version of the third current that is provided to the digital amplitude demodulator.

7. The sub-system of claim 5, wherein the digital amplitude demodulator comprises a multiplier configured to multiply the digital version of the third current by the chopping signal, or a recovered or reproduced version of the chopping signal, to thereby produce the digital demodulation output that is filtered by the digital filter to produce the adjustment signal.

8. The sub-system of claim 2, wherein:

the first current comprises a current produced by one of more photo detectors;

the second current comprises a current produced by one or more further photo detectors;

the first current is applied to the current mirror; and

the current mirror produces the replicated version of the first current.

9. The sub-system of claim 8, wherein:

the subsystem comprises an ambient light sensor (ALS) sub-system;

the first current is indicative of ambient infrared light; and

the second current is indicative of ambient visible light and the ambient infrared light;

the third current is indicative of the ambient visible light and a portion of the ambient infrared light that is proportional to the mismatch error.

10. The sub-system of claim 8, wherein:

the first current is indicative of undesired light;

the second current is indicative of desired light and the undesired light; and

the third current is indicative of the desired light and a portion of the undesired light that is proportional to the mismatch error.

11. The sub-system of claim 1, wherein the sub-system is part of a system, and wherein the mismatch correction circuit is selectively employed in accordance with at least one of the following:

during power-up of the system or the sub-system;

prior to operation of the system;

during operation of the system;

in a background of the system;

during product testing of the system or the sub-system;

periodically;

or

on-demand.

12. A method for reducing a mismatch error associated within an analog circuit, comprising:

(a) accepting a first current and a second current;

(b) using the analog circuit to replicate the first current to thereby produce a replicated version of the first current, and to subtract the replicated version of the first current from the second current to thereby produce a third current;

(c) producing an adjustment signal based on a digital version of the third current, wherein the adjustment signal is indicative of the mismatch error associated with the analog circuit; and

(d) using the adjustment signal to reduce the mismatch error associated with the analog circuit.

13. The method of claim 12, wherein the analog circuit includes a current mirror, and wherein step (d) includes using the adjustment signal to adjust a gain of the current mirror to thereby reduce the mismatch error associated with the analog circuit.

14. The method of claim 12, wherein step (c) is performed using a digital circuit.

15. The method of claim 12, wherein step (c) includes:

(c.1) amplitude demodulating the digital version of the third current to thereby produce a digital demodulated signal; and

(c.2) digitally filtering the digital demodulated signal to thereby produce the adjustment signal.

16. The method of claim 12, wherein:

the first current is indicative of undesired light;

the second current is indicative of desired light and the undesired light; and

the third current is indicative of the desired light and a portion of the undesired light that is proportional to the mismatch error.

17. The method of claim 16, further comprising:

(e) adjusting a parameter or function in dependence on the third current or the digital version of the third current.

18. A system, comprising:

a first sub-system including

an analog circuit configured to replicate a first current to produce a replicated version of the first current, and to subtract the replicated version of the first current from a second current to produce a third current;

an analog-to-digital converter (ADC) configured to produce a digital version of the third current; and

a mismatch correction circuit configured to produce an adjustment signal, indicative of a mismatch error associated with the analog circuit, based on the digital version of the third current;

wherein the adjustment signal is used to reduce the mismatch error associated with the analog circuit; and

a second sub-system configured to be adjusted in dependence on the third current or the digital version of the third current.

19. The system of claim 18, wherein:

the first sub-system comprises an ambient light sensor (ALS) sub-system; and

the second sub-system comprises a display that is configured to have its brightness adjusted in dependence on the third current or the digital version of the third current.

20. The system of claim 18, wherein the system, which includes the first and second sub-systems, comprises at least one of the following:

a mobile phone;

a personal data assistant;

a tablet computer;

a laptop computer;

a media player;

a media recorder;

a television;

or

a gaming module.