Method And Device For Measuring With Synchronous Detection And Correlated Sampling

• US 20080100280A1
• Filed: 04/20/2005
• Published: 05/01/2008
• Est. Priority Date: 04/27/2004
• Status: Active Grant

• Current Assignee: e2v semiconductors SAS (Teledyne Technologies Incorporated)
• Original Assignee: e2v semiconductors SAS (Teledyne Technologies Incorporated)
• Inventors: Masson, Thierry, Salvi, Fabrice
• Granted Patent: US 7,642,766 B2
• Time in Patent Office: Days
• US Class Current: 324/76.38
• CPC Class Codes: G11C 27/026 associated with an amplifier G11C27/028 takes precedence
• CPC Class Codes: H03K 5/249 using clock signals

Abstract

The invention relates to electronic circuits for measuring, by synchronous detection, weak signals whose reference level is not well known and is subject to large fluctuations. A first correlated double sampling is performed between a time T1 situated just before the start of the measurement pulse and a time T2 situated just before the end of the measurement pulse; subsequently, a second correlated double sampling is performed between time T2 and a time T3 situated after the end of the measurement pulse. Finally, the difference between signal levels coming from the two measurements is taken, this difference being a representation of the signal value Vm considered with respect to a reference level that is intermediate between the reference levels at times T1 and T3.

Claims

1. A measurement method with detection that is synchronous with respect to a measurement pulse, wherein, in order to determine the value of a useful signal, a detection is made in synchronism with a short measurement pulse which causes a temporary increase of a signal to be measured, comprising the steps of:

partially compensating for the influence of the variations, over the duration of the pulse, of a reference level of the signal to be measured, performing, within a sample-and-hold circuit;

a first correlated double sampling between a time T1 situated just before the start of the measurement pulse and a time T2 situated just before the end of the measurement pulse, this double sampling supplying a signal measurement Vm considered with respect to a reference level V1 before the start of the pulse;

a second correlated double sampling between time T2 and a time T3 situated after the end of the measurement pulse, this second sampling supplying a representation of the signal measurement Vm considered with respect to a reference level V3 existing after the end of the pulse; and

in establishing a difference between signal levels coming from the two measurements, this difference being a representation of the signal value Vm considered with respect to a reference level that is intermediate between the reference levels at times T1 and T3.

13. The measurement method as claimed in claim 1, wherein the time interval T3−

T2 is substantially equal to T2−

T1.

14. The measurement method as claimed in claim 1, wherein the time interval T3−

T2 is substantially equal to the duration of the measurement pulse.

16. The measurement method as claimed in claim 1, wherein it is applied to the detection of rain on a vehicle windshield, the measurement pulse being a light pulse emitted toward the windshield and reflected with a reflection coefficient that depends on the presence or the absence of rain on the windshield.

17. The measurement method as claimed in claim 13, wherein it is applied to the detection of rain on a vehicle windshield, the measurement pulse being a light pulse emitted toward the windshield and reflected with a reflection coefficient that depends on the presence or the absence of rain on the windshield.

18. The measurement method as claimed in claim 14, wherein it is applied to the detection of rain on a vehicle windshield, the measurement pulse being a light pulse emitted toward the windshield and reflected with a reflection coefficient that depends on the presence or the absence of rain on the windshield.

2-12. -12. (canceled)

20. A measurement device with detection that is synchronous with respect to a measurement pulse which causes a temporary increase in a signal to be measured, comprising:

a sample-and-hold circuit having switching means that are synchronized with the measurement pulse in order to perform by means of the sample-and-hold circuit wherein a first correlated double sampling between a time T1 situated just before the start of the measurement pulse and a time T2 situated just before the end of the measurement pulse, this double sampling supplying a signal measurement Vm considered with respect to a reference level V1 before the start of the pulse;

a second correlated double sampling between time T2 and a time T3 situated after the end of the measurement pulse (preferably T3−

T2=T2−

T1), this second sampling supplying a representation of the signal measurement Vm considered with respect to a reference level V3 existing after the end of the pulse, and the measurement device including means for establishing a difference between signal levels coming from the two measurements, this difference being a representation of the signal value Vm considered with respect to a reference level that is intermediate between the reference levels at times T1 and T3.

21. The device as claimed in claim 20, comprising two sample-and-hold circuits establishing the voltage levels V1-Vm and Vm-V3 and a subtractor at the output of the sample-and-hold circuits for performing the difference sought.

22. The device as claimed in claim 20, wherein the sample-and-hold circuit is differential and comprises a differential amplifier, having two inputs and two outputs, each input being associated with a first and a second input capacitor placed upstream of this input, and being also associated with an integrating capacitor connected between the input and a corresponding output of the amplifier, the signal inputs of the sampler connected to the first input capacitors being crossed with respect to the signal inputs connected to the second input capacitors;

the switching means comprising;

means for making the sample-and-hold circuit operate as a correlated double sample-and-hold using the integrating capacitors and the first input capacitors, by initially applying, across the first input capacitors, a differential input voltage V1p−

V1n representing the reference signal V1 at time T1 and by later applying a differential input voltage Vmp−

Vmn representing the measurement signal Vm at time T2;

means for making the differential sample-and-hold operate as a correlated double sampler, using the integrating capacitors and the second input capacitors, by initially applying, across the second input capacitors, a differential input voltage Vmn-Vmp representing the inverse −

Vm of the useful signal at time T2 and by later applying a differential input voltage V3n−

V3p representing the inverse −

V3 of the reference signal at time T3.

23. The device as claimed in claim 20, wherein the operational amplifiers are equipped with a switch for periodically discharging the integrating capacitor.

24. The device as claimed in claim 23, wherein a means is provided for periodically applying a voltage representing the inverse of the mean value of the output signal of the differential sampler to one input of each operational amplifier.