US 6,035,213 A · Dual-mode cellular telephone system

Abstract

A dual-mode cellular telephone system which is capable of suppressing a narrow-band disturbing signal appearing in a mobile station of a dual-mode cellular telephone system adapted for both an analog system and a digital CDMA system. A CDMA signal from a CDMA base station, and a narrow-band signal from an analog system are received through an antenna by a receiver, whereby they are amplified, subjected to frequency conversion, and input to a variable notch filter. A disturbing signal detection circuit supplies the variable notch filter with a control signal for varying its frequency. Namely, the disturbing signal detection circuit detects a case that an output level of the variable notch filter is at a minimum by changing the notch frequency via a series of sweeping control signals. A control signal at which the output level of the variable notch filter is at a minimum is then fed to the variable notch filter, thereby effectively suppressing any intermodulation distortions present in the mobile station.

Claims10

Dependent claims

A dual-mode cellular telephone system adapted for an analog system and a digital CDMA system and having a mobile station with a narrow-band disturbing signal suppression circuit for suppressing intermodulation distortion produced from signals received from an analog base station, comprising:

a receiver for receiving analog signals from an analog base station and CDMA signals from a CDMA base station;
a notch filter for suppressing a disturbing signal resulting from intermodulation distortion within the received analog and CDMA signals, said notch filter supplied with a variable notch frequency;
a level detecting circuit for monitoring an output level of said receiver;
said level detecting circuit controlling said notch filter to possess a specified notch characteristic only in the case where said output level exceeds a predetermined reference level;
and
a disturbing signal detecting circuit for controlling said variable notch frequency, said disturbing signal detecting circuit selecting a specified value at which said notch filter has a minimum output to control the variable notch frequency supplied to said notch filter.

3 more elements

A dual-mode cellular telephone system adapted for an analog system and a digital CDMA system and having a mobile station with a narrow-band disturbing signal suppression circuit for suppressing intermodulation distortion produced inside the mobile station upon receiving transmission channel signals from an analog base station, comprising:

an antenna for receiving analog signals from an analog base station and CDMA signals from a CDMA base station;
a receiver for receiving analog and CDMA signals input by said antenna;
a notch filter for suppressing a disturbing signal resulting from intermodulation distortion within the received analog and CDMA signals, said notch filter supplied with a variable notch frequency;
a level detecting circuit for monitoring an output level of said receiver;
said level detecting circuit controlling said notch filter to possess a specified notch characteristic only in the case where said output level exceeds a predetermined reference level;
and
a disturbing signal detecting circuit for controlling said variable notch frequency, said disturbing signal detecting circuit selecting a specified value at which said notch filter has a minimum output to control the variable notch frequency supplied to said notch filter.

4 more elements

Dependencies are inferred from the claim text.

Dual-mode cellular telephone system

Life of this patent

Dual-mode cellular telephone system

Life of this patent

Abstract

Claims10