Multi-bit ADC with sigma-delta modulation
First Claim
Patent Images
1. An oximeter apparatus comprising:
- a sigma-delta modulator having an input coupled to receive an analog sensor signal;
a first switching circuit, coupled to said input, for switching between connecting first and second reference voltages to said input; and
a feedback circuit, coupled to an output of said sigma-delta modulator, for controlling the switching between said first and second reference voltages by said switching circuit.
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Abstract
An oximeter uses a sigma-delta modulator and a multi-bit ADC with PWM feedback enabling high precision multi-bit conversion. Demodulation is done in software, thus requiring only a single hardware path for both red and IR. Multiple capacitors are switched into the integrator in the sigma-delta modulator, with different capacitors for red, IR and dark signals, thus enabling the use of the single hardware path. A switching circuit at the input of the sigma-delta modulator acts as a sample and hold, controlled by the PWM feedback.
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Citations
19 Claims
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1. An oximeter apparatus comprising:
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a sigma-delta modulator having an input coupled to receive an analog sensor signal;
a first switching circuit, coupled to said input, for switching between connecting first and second reference voltages to said input; and
a feedback circuit, coupled to an output of said sigma-delta modulator, for controlling the switching between said first and second reference voltages by said switching circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An oximeter apparatus comprising:
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a sigma-delta modulator having an input coupled to receive an analog sensor signal;
a first switching circuit, coupled to said input, for switching between connecting first and second reference voltages to said input;
a multiple bit analog-to-digital converter coupled to said output of said sigma-delta modulator to provide a digital output; and
a feedback circuit, coupled to an output of said multiple bit analog-to-digital converter, for controlling the switching between said first and second reference voltages by said switching circuit, said feedback circuit providing a pulse width modulated signal to said switching circuit; and
a resistor coupled between said switching circuit and said input of said sigma-delta modulator.
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14. An oximeter apparatus comprising:
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a sigma-delta modulator having an input coupled to receive an analog sensor signal, wherein said sigma-delta modulator includes an operational amplifier configured as an integrator;
a switching circuit configured to function as a sample and hold by alternately couple said input to inverting and non-inverting inputs of said operational amplifier;
a feedback circuit coupled between an output and said input of said sigma-delta modulator; and
a control circuit, coupled to said feedback circuit, for controlling the switching of said switching circuit.
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15. An oximeter apparatus comprising:
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a sigma-delta modulator having an input coupled to receive an analog sensor signal, wherein said sigma-delta modulator includes an integrator;
at least first and second capacitors; and
a capacitor switching circuit for connecting said first capacitor into said integrator upon receipt of a first sensor signal, and connecting said second capacitor into said integrator upon receipt of a second sensor signal.
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16. The oximeter apparatus of claim 16 wherein said first sensor signal is a red signal and said second sensor signal is an infrared signal.
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17. The oximeter apparatus of claim 17 further comprising a third capacitor for connecting into said integrator upon receipt of a dark signal between said red and infrared signals.
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18. The oximeter apparatus of claim 18 further comprising a fourth capacitor for connecting into said integrator for a second dark signal between said infrared signal and said red signal.
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19. An oximeter apparatus comprising:
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a sigma-delta modulator having an input coupled to receive an analog sensor signal;
a multiple bit analog-to-digital converter coupled to said output of said sigma-delta modulator to provide a digital output;
a feedback circuit, coupled between an output of said analog-to-digital converter and said input of said sigma-delta modulator; and
a memory containing a program for demodulating said digital output into red and infrared digital signals wherein a single signal path through said sigma-delta modulator is used for modulated red and infrared signals.
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Specification