Hitachi, Ltd.

Kokusai Electric Co., Ltd.

Atushi Hoshi

Nobuo Tsukamoto

Hiroshi Noguchi

Arata Nakagoshi

Kazuo Yamakido

Jiroh Sakaguchi

Isamu Mitomo

Masato Horaguchi

A method of controlling the time constant of a filter for use in a radio receiver which receives a signal, transmitted from a transmitting station at a predetermined period, intermittently at the predetermined period and demodulates and delivers the received signal, a filter circuit having the time constant control function based on the method, and a radio receiver having the filter circuit. Preferably, the filter has its time constant switchable stepwise and specifically, parallel connection of capacitors or shortcircuiting of resistors is controlled by turning on/off switches. A controller within the filter circuit or the radio receiver performs control for applying a predetermined periodical signal (or standard pulse signal) to the filter and controlling the time constant of the filter in accordance with an output signal (or triangular pulse) during a first time zone within each operation interval for the intermittent reception and for filtering the signal from the transmitting station and causing a demodulating circuit to demodulate and deliver a filtered signal.

Method of controlling filter time constant and filter circuit having the

The invention relates to a demodulator and to a radio receiver having such a demodulator and, more particularly, to a demodulator for demodulating signals which were digitized by a direct detecting method in which a circuit scale is small and an electric power consumption is small. Particularly, it is a characteristic that a limiter in the demodulator comprises: a circuit for obtaining absolute values of the digital signals (I signal, Q signal) which are produced from an angle modulated wave and whose phases are mutually orthogonal; a circuit for outputting the sum (.vertline.I.vertline.+.vertline.Q.vertline.) of the absolute values or the larger one M(.vertline.I.vertline., .vertline.Q.vertline.) of the absolute values; a controller for producing a control signal according to an output of the above circuit; and scalers which change the amplitudes of the first and second digital signals in accordance with the control signal and which are constructed by a plurality of shift registers and adders.

Demodulator and radio receiver having such a demodulator

Growing community of inventors

Tokyo, Japan

Atushi Hoshi