Patent ID: 7664811

Claim:
A filter apparatus, comprising: a radio frequency converter that converts a radio frequency signal to current; a plurality of sampling capacitors that accumulate the current as a charge; a reader that reads a voltage from the plurality of sampling capacitors; positive polarity reading selectors that connect terminals of one side of the plurality of sampling capacitors to the reading section; negative polarity reading selectors that connect terminals of an other side of the plurality of sampling capacitors to the reading section; negative polarity ground connectors that connect the terminals of the one side of the plurality of sampling capacitors to a common ground; positive polarity ground connectors that connect the terminal of the other side of the plurality of sampling capacitors to the common ground; and a timing controller that outputs a control signal to each of the positive polarity reading selectors, the negative polarity reading selectors, the negative polarity ground connectors, and the positive polarity ground connectors, and that controls operation timing of each of the positive polarity reading selectors, the negative polarity reading selectors, the negative polarity ground connectors, and the positive polarity ground connectors.