Readout Circuit for Resistive and Capacitive Sensors

Abstract

A readout circuit for resistive and capacitive sensors includes a first input coupled to a reference resistor in a first mode of operation and coupled to a resistive sensor in a second mode of operation; a second input coupled to a capacitive sensor in the first mode of operation and coupled to a reference capacitor in the second mode of operation; and an output for providing a capacitive sensor data stream in the first mode of operation and for providing a resistive sensor data stream in the second mode of operation.

What is claimed is: 
     
         1 . A method of operating a circuit in a device, the method comprising:
 coupling a resistor and a capacitive sensor to first and second inputs of the circuit in a first mode of operation;   coupling a capacitor and a resistive sensor to first and second inputs of the circuit in a second mode of operation;   providing a capacitive sensor data stream at an output in the first mode of operation; and   providing a resistive sensor data stream at the output in a the second mode of operation.   
     
     
         2 . The method of  claim 1 , further comprising:
 selecting the capacitive sensor from a plurality of capacitive sensors resident in the device.   
     
     
         3 . The method of  claim 1 , further comprising:
 selecting the resistive sensor from a plurality of resistive sensors resident in the device.   
     
     
         4 . The method of  claim 1 , further comprising:
 integrating the resistive sensor and the circuit together in an integrated circuit.   
     
     
         5 . The method of  claim 1 , further comprising:
 integrating the capacitive sensor and the circuit together in an integrated circuit.   
     
     
         6 . The method of  claim 1 , further comprising:
 coupling a resistive sensor and a capacitive sensor to the first and second inputs of the circuit in a third mode of operation; and   providing a composite sensor data stream at the output in the third mode of operation.   
     
     
         7 . A method of operating a circuit, the method comprising:
 coupling a resistor to a first two node input of the circuit;   coupling a capacitor to a second two node input of the circuit;   converting a voltage at the first two node input into a switched current output;   using the capacitor, integrating the switched current output to generate an integrated voltage;   comparing the integrated voltage to first and second threshold voltages to generate first and second logic signals; and   combining the first and second logic signals to generate first and second variable frequency output signals.   
     
     
         8 . The method of  claim 7 , further comprising controlling the switched current output with the first and second variable frequency output signals. 
     
     
         9 . The method of  claim 7 , wherein the integrated voltage comprises a triangular voltage waveform. 
     
     
         10 . The method of  claim 7 , wherein combining the first and second logic signals comprises latching the first and second logic signals. 
     
     
         11 . The method of  claim 7 , wherein the resistor comprises a resistive sensor, the capacitor comprises a fixed capacitor reference, and at least one of the first and second logic signals comprises data based on resistive variations of the resistive sensor. 
     
     
         12 . The method of  claim 7 , wherein the resistor comprises a fixed resistor reference, the capacitor comprises a capacitive sensor, and at least one of the first and second logic signals comprises data based on capacitive variations of the capacitive sensor. 
     
     
         13 . The method of  claim 7 , wherein the resistor comprises a resistive sensor, the capacitor comprises a capacitive sensor, and at least one of the first and second logic signals comprises composite serial data based on resistive variations of the resistive sensor and on capacitive variations of the capacitive sensor. 
     
     
         14 . A method of operating a circuit in a device, the method comprising:
 coupling a resistor and a capacitive sensor to first and second inputs of the circuit in a first mode of operation;   coupling a capacitor and a resistive sensor to first and second inputs of the circuit in a second mode of operation;   converting a voltage at the first input into a switched current output;   integrating the switched current output to generate an integrated voltage;   comparing the integrated voltage to first and second threshold voltages to generate first and second logic signals; and   combining the first and second logic signals to generate a variable frequency capacitive sensor data stream in the first mode of operation and to generate a variable frequency resistive sensor data stream in the second mode of operation.   
     
     
         15 . The method of  claim 14 , further comprising:
 coupling a resistive sensor and a capacitive sensor to the first and second inputs of the circuit in a third mode of operation; and   providing a composite sensor data stream in the third mode of operation.   
     
     
         16 . The method of  claim 14 , further comprising:
 selecting the capacitive sensor from a plurality of capacitive sensors resident in the device.   
     
     
         17 . The method of  claim 14 , further comprising:
 selecting the resistive sensor from a plurality of resistive sensors resident in the device.   
     
     
         18 . The method of  claim 14 , further comprising controlling the switched current output with the variable frequency capacitive sensor data stream in the first mode of operation and with the variable frequency resistive sensor data stream in the second mode of operation. 
     
     
         19 . The method of  claim 14 , wherein the integrated voltage comprises a triangular voltage waveform. 
     
     
         20 . The method of  claim 14 , wherein combining the first and second logic signals comprises latching the first and second logic signals.