Successive approximate capacitance measurement circuit
First Claim
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1. A method of measuring a capacitance of a device under test (“
- DUT”
) capacitor, comprising;
generating a selectable current having a current magnitude, using a variable current source;
switching between charging the DUT capacitor with the selectable current by driving the selectable current into the DUT capacitor and discharging the DUT capacitor at a switching frequency;
comparing a first voltage, responsive to a second voltage on the DUT capacitor, to a reference voltage to determine whether the first voltage is greater than or less than the reference voltage; and
adjusting at least one of the switching frequency, the current magnitude, or the reference voltage until the first voltage is substantially equal to the reference voltage;
monitoring the first voltage while holding the switching frequency and current magnitude steady; and
indicating when the first voltage crosses over the reference voltage.
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Abstract
A capacitance measurement circuit includes a current source, a switch, and a comparator. The current source is coupled to drive a current through a circuit node. The switch is coupled to the circuit node to switch the current into a device under test (“DUT”) capacitor. The comparator includes first and second input ports. The comparator is coupled to compare a first voltage received on the first input port against a reference voltage received on the second input port. The first voltage is related to the current driven through the circuit node, a frequency at which the switch is switched, and a capacitance of the DUT capacitor.
240 Citations
8 Claims
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1. A method of measuring a capacitance of a device under test (“
- DUT”
) capacitor, comprising;generating a selectable current having a current magnitude, using a variable current source; switching between charging the DUT capacitor with the selectable current by driving the selectable current into the DUT capacitor and discharging the DUT capacitor at a switching frequency; comparing a first voltage, responsive to a second voltage on the DUT capacitor, to a reference voltage to determine whether the first voltage is greater than or less than the reference voltage; and adjusting at least one of the switching frequency, the current magnitude, or the reference voltage until the first voltage is substantially equal to the reference voltage; monitoring the first voltage while holding the switching frequency and current magnitude steady; and indicating when the first voltage crosses over the reference voltage. - View Dependent Claims (2, 3, 4, 5, 7, 8)
- DUT”
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6. A method of measuring a capacitance of a device under test (“
- DUT”
) capacitor, comprising;generating a current having a current magnitude; switching between charging the DUT capacitor with the current and discharging the DUT capacitor at a switching frequency; adjusting at least one of the switching frequency or the current magnitude multiple times; after each adjustment to the switching frequency or the current magnitude, comparing a first voltage, responsive to a second voltage on the DUT capacitor, to a reference voltage to determine whether the first voltage is greater than or less than the reference voltage; adjusting at least one of the switching frequency or the current magnitude until the first voltage is substantially equal to the reference voltage; changing the reference voltage by a first margin; monitoring the first voltage while holding the switching frequency and current magnitude steady; and indicating when the first voltage crosses over the reference voltage.
- DUT”
Specification