Capacitance sensor using relaxation oscillators
First Claim
1. An apparatus, comprising:
- a comparator circuit with hysteresis including a first input and an output;
a capacitor coupled to the first input of the comparator circuit with hysteresis;
a current driver coupled to the output of the comparator circuit with hysteresis and to the capacitor, the current driver to reciprocally source and sink a drive current through a terminal of the capacitor to oscillate a voltage potential at the terminal of the capacitor between a low reference potential and a high reference potential responsive to the output of the comparator circuit with hysteresis;
a processor coupled to execute instructions;
a current source to generate a first reference current; and
a scaler unit coupled to receive a digital current control signal from the processor and to selectively scale the first reference current in response to the digital current control signal to generate a second reference current to provide to the current driver.
6 Assignments
0 Petitions
Accused Products
Abstract
An apparatus that may be used to sense capacitance, as well as other functions. The apparatus includes a comparator circuit with hysteresis, a capacitor, and a current driver. The comparator circuit with hysteresis includes a first input and an output. The capacitor is coupled to the first input of the comparator circuit with hysteresis. The current driver is coupled to the output of the comparator circuit with hysteresis and to the capacitor. The current driver reciprocally sources and sinks a drive current through a terminal of the capacitor to oscillate a voltage potential at the terminal of the capacitor between a low reference potential and a high reference potential. The current driver is responsive to the output of the comparator circuit with hysteresis.
359 Citations
20 Claims
-
1. An apparatus, comprising:
-
a comparator circuit with hysteresis including a first input and an output; a capacitor coupled to the first input of the comparator circuit with hysteresis; a current driver coupled to the output of the comparator circuit with hysteresis and to the capacitor, the current driver to reciprocally source and sink a drive current through a terminal of the capacitor to oscillate a voltage potential at the terminal of the capacitor between a low reference potential and a high reference potential responsive to the output of the comparator circuit with hysteresis; a processor coupled to execute instructions; a current source to generate a first reference current; and a scaler unit coupled to receive a digital current control signal from the processor and to selectively scale the first reference current in response to the digital current control signal to generate a second reference current to provide to the current driver. - View Dependent Claims (2, 3, 4, 5, 6)
-
-
7. A method to sense a capacitance, comprising:
-
charging and discharging a reference capacitor with a first drive current generated by a first oscillator oscillating at a first frequency; charging and discharging a device under test (“
DUT”
) capacitor with a second drive current generated by a second oscillator oscillating at a second frequency, wherein the first and second drive currents are scaled from a common reference current; andmeasuring a capacitance change across the DUT capacitor based on a relative change between the first and second frequencies. - View Dependent Claims (8, 9, 10, 11, 12, 13)
-
-
14. A capacitance sensor, comprising:
-
a first oscillator coupled to charge and discharge a reference capacitor with a first drive current at a first frequency, the first oscillator including; a comparator circuit with hysteresis including a first input coupled to the reference capacitor and an output; and a current driver coupled to the output of the comparator circuit with hysteresis and to the reference capacitor, the current driver to reciprocally source and sink the first drive current through a terminal of the reference capacitor to oscillate a voltage potential at the terminal of the reference capacitor between a low reference potential and high reference potential responsive to the output of the comparator circuit with hysteresis; a second oscillator to charge and discharge a device under test (“
DUT”
) capacitor with a second drive current at a second frequency; anda frequency comparator coupled to the first and second oscillators to output a signal indicative of a capacitance change across the DUT capacitor based on a frequency difference between the first and second frequencies. - View Dependent Claims (15, 16, 17, 18, 19, 20)
-
Specification