Direct change-over receiver and receiving method of movable radio equipment and radio-frequency signal

Abstract

In a direction conversion receiver, a quadrature demodulator produces differential signals in a baseband on the basis of a local signal of a frequency synthesizer, with the differential signals being inputted through a first low pass filter, a gain control amplifier and an amplifier to a control unit and a direct current component between the differential signals being extracted in a second low pass filter. In addition, an offset compensating section reduces an offset voltage while the control unit outputs a control signal for the control of the gain control amplifier. The second low pass filter includes a time constant circuit for determining a time constant through the use of resistors and a capacitor, and a time constant changing section. A time constant control unit controls the time constant changing section for a predetermined period of time after the control unit outputs data for the change of a frequency of the local signal so that the time constant of the time constant circuit decreases. This shortens the time needed for the settlement of automatic gain control and prevents the deterioration of demodulation accuracy during a call.

Description

technical field [0001] The present invention relates to a direct conversion receiver for a mobile radio or the like, a mobile radio using said direct conversion receiver and a method of receiving RF signals. Background technique [0002] Fig. 5 is a block diagram showing the circuit arrangement of a conventional typical direct conversion receiver. In the illustrated illustration, the quadrature demodulator 1 is used to receive an RF (radio frequency) signal obtained by performing quadrature modulation on the carrier phase and amplitude, and use it as an input signal, and is also used to receive The local signal Lo serves as another input signal in order to output signals i, ix (i and ix denote differential signals) and q, qx (q and qx denote differential signals) belonging to the baseband, which have an orthogonal relationship with each other. Receiving baseband unit 2 is connected to the output of quadrature demodulator 1 for receiving baseband signals i and ix, and receiv...

AI Technical Summary

Problems solved by technology

[0020] Also, in the case where the direct conversion receiver is used for a mobile radio such as a portable telephone, since it takes time to determine the automatic gain control during the queue operation, there arises a problem of prolonging the Reduced waiting time by reducing receiver operating time during waiting operations

[0021] Also, the quality of the call is degraded due to the DC variation under gain control conditions during the call

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