Background sensor diagnostic for multi-channel ADC

• US 8,884,629 B1
• Filed: 05/09/2011
• Issued: 11/11/2014
• Est. Priority Date: 07/23/2010
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Kumar, D V J Ravi, Srinivas, Theertham, Ghorpade, Gururaj
• Primary Examiner(s): Phan, Huy Q
• Assistant Examiner(s): SPLIT, JAMES G
• Application Number:
  US13/103,894
• Time in Patent Office: 1,282 Days
• Field of Search: 324/500, 324/522, 324/537, 324/555, 324/523, 702182-185, 341118-121, 341/141, 370/241, 370/250, 370/251
• US Class Current: 324/537
• CPC Class Codes: H03F 1/0277 Selecting one or more amplifiers from a plurality of amplifiers
• CPC Class Codes: H03F 2200/261 Amplifier which being suitable for instrumentation applications
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 2200/411 the output amplifying stage of an amplifier comprising two power stages
• CPC Class Codes: H03F 2200/78 A comparator being used in a controlling circuit of an amplifier
• CPC Class Codes: H03F 2203/45366 the AAC comprising multiple transistors parallel coupled at their gates only, e.g. in a cascode dif amp, only those forming the composite common source transistor
• CPC Class Codes: H03F 2203/45396 the AAC comprising one or more switches
• CPC Class Codes: H03F 2203/45614 the IC comprising two cross coupled switches
• CPC Class Codes: H03F 2203/45616 the IC comprising more than one switch, which are not cross coupled
• CPC Class Codes: H03F 2203/45644 the LC comprising a cross coupling circuit, e.g. comprising two cross-coupled transistors
• CPC Class Codes: H03F 2203/45726 the LC comprising more than one switch, which are not cross coupled
• CPC Class Codes: H03F 2203/7221 the gated amplifier being switched on or off by a switch at the output of the amplifier
• CPC Class Codes: H03F 2203/7236 the gated amplifier being switched on or off by putting into parallel or not, by choosing between amplifiers by (a ) switch(es)
• CPC Class Codes: H03F 3/38 DC amplifiers with modulator at input and demodulator at output; Modulators or demodulators specially adapted for use in such amplifiers switched capacitor amplifiers H03F3/005
• CPC Class Codes: H03F 3/393 with field-effect devices
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence
• CPC Class Codes: H03F 3/45192 Folded cascode stages
• CPC Class Codes: H03F 3/45695 by using feedforward means H03F3/45744 takes precedence
• CPC Class Codes: H03F 3/72 Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal
• CPC Class Codes: H03M 1/1004 without interrupting normal operation, e.g. by providing an additional component for temporarily replacing components to be tested or calibrated H03M1/1009, H03M1/1071 take precedence
• CPC Class Codes: H03M 1/122 : Shared using a single converter or a part thereof for multiple channels, e.g. a residue amplifier for multiple stages

Abstract

A digital sensing device includes a sensor diagnostic system for detecting sensor fault conditions. The sensor diagnostic system including an input multiplexer applying a first burnout current or a second burnout current to a selected input channel and a near-rail detector configured to detect when an input voltage of the digital sensing device is near a positive power supply or near a negative power supply. The burnout current injection is applied without interfering with the sensor data. In other embodiments, the sensor diagnostic system may further include an overload detector configured to detect an overflow or underflow condition at the analog-to-digital converter. The sensor diagnostic system may further include a window comparator to detect when the ADC digital output is near a zero digital value. Finally, the sensor diagnostic system may further include a sensor flag generator to generate data flags indicative of sensor fault conditions.

Claims

1. A digital sensing device including a plurality of input channels receiving one or more analog input signals from a sensor, the digital sensing device comprising:

an input multiplexer configured to select a pair of input channels from the plurality of input channels and to connect the selected input channel pair to respective output nodes;

an input buffer comprising a first input terminal and a second input terminal coupled to respective output nodes of the input multiplexer, the input buffer configured to generate buffered signals from the analog input signals selected by the input multiplexer;

an analog-to-digital converter configured to receive the buffered signals and to generate digital values indicative of the selected analog input signals; and

a sensor diagnostic system configured to detect sensor fault conditions, comprising;

a first burnout current source providing a first burnout current and a second burnout current source providing a second burnout current, the first and second burnout current sources being multiplexed by the input multiplexer to be switchably connected to a selected input channel of the plurality of input channels, the input multiplexer being configured to apply the first or second burnout current to an input channel that is either currently selected or not currently selected by the input multiplexer as an input channel of the selected input channel pair; and

a near-rail detector coupled to the first and second input terminals of the input buffer and configured to detect when a voltage on one of the first and second input terminals of the input buffer is near a positive power supply or near a negative power supply and to generate a signal indicative of a near-rail condition.

2. The digital sensing device of claim 1, wherein the analog-to-digital converter comprises a Σ

Δ

modulator configured to generate a single bit digitized data stream having a density of logic ones representative of the magnitude of the analog input signal, wherein the sensor diagnostic system further comprises;

an overload detector configured to detect when the data stream generated by the Σ

Δ

modulator having a number of consecutive ones or zeros that exceeds a first threshold, the overload detector generating a signal indicative of an overload condition in response to the data stream generated by the Σ

Δ

modulator having a number of consecutive ones or zeros exceeding the first threshold.

3. The digital sensing device of claim 1, wherein the sensor diagnostic system further comprises:

a window comparator configured to detect when the digital values generated by the analog-to-digital converter are within a given comparison window, the comparison window defining values within a positive threshold and a negative threshold around a zero digital value.

4. The digital sensing device of claim 3, wherein the positive threshold and the negative threshold defining the comparison window are programmable.

5. The digital sensing device of claim 1, wherein the sensor diagnostic system further comprises:

a sensor flag generator configured to generate data flags indicative of the sensor fault conditions, including the near-rail conditions detected by the near-rail detector.

6. The digital sensing device of claim 1, wherein the input multiplexer is operated in a scan mode to select each of the plurality of input channels in turn and to apply the first or second burnout current to an input channel that was previously selected by the input multiplexer as an input channel of the selected input channel pair.

7. The digital sensing device of claim 6, wherein the input multiplexer is operated so that the first or second burnout current is applied to an input channel not currently being evaluated by the analog-to-digital converter as an input channel of the selected input channel pair, so that normal ADC operation is not affected by the burnout current injection, and the burnout current injection does not affect the analog input signals from the sensor, the sensor diagnostic system being operated to detect sensor fault conditions entirely in the background of the normal ADC operation.

8. A digital sensor system, the digital sensing device comprising:

a sensor configured to sense a physical state or condition, and output an analog signal corresponding to a sensed physical stat or condition;

a sensor analog front end (AFE) configured to receive the analog signal from the sensor, the AFE including;

a plurality of input channels receiving one or more analog input signals from the sensor

an input multiplexer configured to select a pair of input channels from the plurality of input channels and to connect the selected input channels to output nodes;

an input buffer comprising a first input terminal and a second input terminal coupled to respective output nodes of the input multiplexer, the input buffer configured to generate buffered signals from the analog input signals selected by the input multiplexer;

an analog-to-digital converter configured to receive the buffered signals and to generate digital values indicative of the selected analog input signals; and

a sensor diagnostic system configured to detect sensor fault conditions, comprising;

a first burnout current source providing a first burnout current and a second burnout current source providing a second burnout current, the first and second burnout current sources being multiplexed by the input multiplexer to be switchably connected to a selected input channel pair of the plurality of input channels, the input multiplexer being configured to apply the first and second burnout currents to an input channel pair that is either currently selected or not currently selected by the input multiplexer independent of the selection of a pair of input channels; and

a near-rail detector coupled to the first and second input terminals of the input buffer and configured to detect when a voltage on one of the first and second input terminals of the input buffer is near a positive power supply or near a negative power supply and to generate a signal indicative of a near-rail condition.

9. The system of claim 8, wherein the analog-to-digital converter comprises a Σ

Δ

modulator configured to generate a single bit digitized data stream having a density of logic ones representative of the magnitude of the analog input signal, wherein the sensor diagnostic system further comprises;

an overload detector configured to detect when the data stream generated by the Σ

Δ

modulator having a number of consecutive ones or zeros that exceeds a first threshold, the overload detector generating a signal indicative of an overload condition in response to the data stream generated by the Σ

Δ

modulator having a number of consecutive ones or zeros exceeding the first threshold.

10. The system of claim 8, wherein the sensor diagnostic system further comprises:

a window comparator configured to detect when the digital values generated by the analog-to-digital converter are within a given comparison window, the comparison window defining values within a positive threshold and a negative threshold around a zero digital value.

11. The system of claim 10, wherein the positive threshold and the negative threshold defining the comparison window are programmable.

12. The system of claim 8, wherein the sensor diagnostic system further comprises:

a sensor flag generator configured to generate data flags indicative of the sensor fault conditions, including the near-rail conditions detected by the near-rail detector.

13. The system of claim 8, wherein the input multiplexer is operated in a scan mode to select each of the plurality of input channels in turn and to apply the first or second burnout current to an input channel that was previously selected by the input multiplexer as an input channel of the selected input channel pair.

14. The system of claim 13, wherein the input multiplexer is operated so that the first or second burnout current is applied to an input channel not currently being evaluated by the analog-to-digital converter as an input channel of the selected input channel pair, so that normal ADC operation is not affected by the burnout current injection, and the burnout current injection does not affect the analog input signals from the sensor, the sensor diagnostic system being operated to detect sensor fault conditions entirely in the background of the normal ADC operation current injection.

15. An sensor analog front end (AFE) including a plurality of input channels receiving one or more analog input signals from a sensor, the sensor AFE comprising:

an input multiplexer configured to select a pair of input channels from the plurality of input channels and to connect the selected input channels to output nodes;

an input buffer comprising a first input terminal and a second input terminal coupled to respective output nodes of the input multiplexer, the input buffer configured to generate buffered signals from the analog input signals selected by the input multiplexer;

an analog-to-digital converter configured to receive the buffered signals and to generate digital values indicative of the selected analog input signals; and

a sensor diagnostic system configured to detect sensor fault conditions, including a first burnout current source providing a first burnout current and a second burnout current source providing a second burnout current, the first and second burnout current sources being multiplexed by the input multiplexer to be switchably connected to a selected input channel pair of the plurality of input channels, the input multiplexer being configured to apply the first and second burnout currents to an input channel pair that is either currently selected or not currently selected by the input multiplexer independent of the selection of a pair of input channels.

16. The sensor AFE of claim 15, wherein the sensor diagnostic system further comprises:

a near-rail detector coupled to the first and second input terminals of the input buffer and configured to detect when a voltage on one of the first and second input terminals of the input buffer is near a positive power supply or near a negative power supply and to generate a signal indicative of a near-rail condition.

17. The sensor AFE of claim 16, wherein the sensor diagnostic system further comprises:

a sensor flag generator configured to generate data flags indicative of the sensor fault conditions, including the near-rail conditions detected by the near-rail detector.

18. The sensor AFE of claim 15, wherein the input multiplexer is operated in a scan mode to select each of the plurality of input channels in turn and to apply the first or second burnout current to an input channel that was previously selected by the input multiplexer as an input channel of the selected input channel pair.

19. The sensor AFE of claim 18, wherein the input multiplexer is operated so that the first or second burnout current is applied to an input channel not currently being evaluated by the analog-to-digital converter as an input channel of the selected input channel pair, so that normal ADC operation is not affected by the burnout current injection, and the burnout current injection does not affect the analog input signals from the sensor, the sensor diagnostic system being operated to detect sensor fault conditions entirely in the background of the normal ADC operation current injection.