Polyphase filter and receiver using the same

A polyphase filter comprising:

• a plurality of bridge circuits, each said bridge circuit being composed of four serial connection circuits, and each said serial connection circuit being composed of a resistor and a capacitor serially connected,
• connection points between adjacent ones of the four serial connection circuits being provided as signal input terminals,
• connection points between the resistors and the capacitors in the four serial connection circuits being provided as signal output terminals,
• so that the plurality of the bridge circuits are connected in cascade via the signal input terminals and the signal output terminals,
• a first input signal being supplied to a first pair of opposing signal input terminals of the bridge circuit in a first stage of the plurality of the bridge circuit connected in cascade,
• a second input signal being supplied to a second pair of opposing signal input terminals of the bridge circuit in the first stage,
• a first pair of adjacent signal output terminals of the bridge circuits in a last stage of the plurality of bridge circuits connected in cascade being connected with each other to provide a first signal output terminal,
• a second pair of adjacent signal output terminals of the bridge circuit in the last stage being connected with each other to provide a second signal output terminal, so as to obtain output signal from the first and second signal output terminals;
• wherein
• the polyphase filter as a whole is fabricated into an integrated circuit;
• the capacitor is composed of a metal-insulator-semiconductor capacitor;
• and
• the metal-insulator-semiconductor capacitor is fabricated into the integrated circuit so that a parasitic capacitor formed by a p-n junction between the metal-insulator-semiconductor capacitor and a semiconductor substrate of the metal-insulator-semiconductor capacitor and accompanying said metal-insulator-semiconductor capacitor is connected between an input side of the resistor of a succeeding serial connection circuit and ground.

A receiver comprising:

• a tuning circuit for extracting a desired signal having a target frequency from received signals;
• a first mixer circuit and a second mixer circuit to which the desired signal extracted by the tuning circuit is supplied;
• a circuit for supplying to the first and the second mixer circuits a first local oscillation signal and a second local oscillation signal being different in phase by 90° from each other;
• a polyphase filter to which a first intermediate frequency signal and a second intermediate frequency signal being different in phase by 90° from each other output from the first and the second mixer circuits are supplied;
• and
• a demodulation circuit to which an output signal from the polyphase filter is supplied;
• wherein,
• the polyphase filter is as a whole fabricated into an integrated circuit;
• and
• includes a plurality of bridge circuits in a cascade connection, each said bridge circuit being composed of four serial connection circuits, and each said serial connection circuit being composed of a resistor and a capacitor serially connected;
• the capacitor being composed of a metal-insulator-semiconductor capacitor;
• and
• the metal-insulator-semiconductor capacitor being fabricated into the integrated circuit so that a parasitic capacitor formed by a p-n junction between the metal-insulator-semiconductor capacitor and a semiconductor substrate of the metal-insulator-semiconductor capacitor and accompanying said metal-insulator-semiconductor capacitor is connected between an input of the resistor of a succeeding serial connection circuit and ground.