CAPACITANCE-TO-DIGITAL INTERFACE CIRCUIT FOR DIFFERENTIAL PRESSURE SENSOR
First Claim
1. A two-phase, second order capacitance-to-digital (CD) modulator for converting a first capacitance CX and a second capacitance CY to a pulse code modulated (PCM) signal representative of (CX-CY)/(CX+CY), the CD modulator comprising:
- a first stage sigma-delta integrator for selectively forming charge packets in CX and CY during a first phase, and integrating charge from CX and CY during a second phase to produce a first stage output VOUT1, wherein the first stage sigma-delta integrator holds VOUT1 constant during the first phase;
a second stage sigma-delta integrator for sampling the first stage output VOUT1 during the first phase, and integrating the sampled first stage output during the second phase to produce a second stage output VOUT2; and
a quantizer for converting the second stage output VOUT2 to the PCM signal.
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Abstract
A two phase, second order capacitance-to-digital (CD) modulator includes a first stage sigma-delta integrator that forms charge packets as a function of sensor capacitance during an auto-zero phase and integrates the packets during an integration phase to produce an output voltage. The first stage integrator holds its output voltage during the auto-zero phase, so that a second stage sigma-delta integrator can sample the first stage output voltage during the auto-zero phase and integrate the sampled voltage during the integration phase.
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Citations
20 Claims
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1. A two-phase, second order capacitance-to-digital (CD) modulator for converting a first capacitance CX and a second capacitance CY to a pulse code modulated (PCM) signal representative of (CX-CY)/(CX+CY), the CD modulator comprising:
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a first stage sigma-delta integrator for selectively forming charge packets in CX and CY during a first phase, and integrating charge from CX and CY during a second phase to produce a first stage output VOUT1, wherein the first stage sigma-delta integrator holds VOUT1 constant during the first phase;
a second stage sigma-delta integrator for sampling the first stage output VOUT1 during the first phase, and integrating the sampled first stage output during the second phase to produce a second stage output VOUT2; and
a quantizer for converting the second stage output VOUT2 to the PCM signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A two-phase, second order capacitance-to-digital (CD) modulator comprising:
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a first stage sigma-delta integrator for selectively forming charge packets as a function of sensor capacitance during an auto-zero phase, and integrating the charge packets during an integration phase to produce a first stage output VOUT1 that changes only in the integration phase;
a second stage sigma-delta integrator for sampling the first stage output VOUT during the auto-zero phase, and integrating the sampled first stage output during the integration phase to produce a second stage output VOUT2; and
a quantizer for converting the second stage output VOUT2 to a pulse code modulated signal. - View Dependent Claims (11, 12, 13, 14)
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15. A differential pressure transmitter comprising:
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a first capacitance pressure sensor;
a second capacitance pressure sensor;
a first stage sigma-delta integrator for selectively forming charge packets as a function of capacitance of one of the first and second capacitance pressure sensors during a first phase, and integrating charge during a second phase to produce a first stage output VOUT1, wherein the first stage output VOUT1 is not reset between successive second phase periods;
a second stage sigma-delta integrator for sampling the first stage output VOUT1 during the first phase, and integrating the sampled first stage output during the second phase to produce a second stage output VOUT2; and
a quantizer for converting the second stage output VOUT2 to a pulse code modulated (PCM) signal that is a function of pressure sensed by the first and second capacitance pressure sensors. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification