Patent ID: 6212367
Filing Date: 2001-04-03
Classification: H03J,H04B

Abstract:
A mobile phone apparatus comprising:a modulator for producing a signal to be transmitted in a transmit band;a power amplifier for supplying the signal to be transmitted to an aerial;a tunable filter disposed between the modulator and the power amplifier and having a passband and an attenuation band; anda control circuit for tuning the filter such that the passband is at the transmit band and the attenuation band is at a receive band of the apparatus;wherein the filter is voltage tunable,wherein the control circuit comprises a power detector connected to the output of the filter and a control loop for varying the tuning voltage of the filter until a predetermined power is detected,wherein the control loop comprises a signal generator for generating a varying voltage for the filter and a feedback circuit whose input is connected to the power detector and whose output is superimposed on the varying voltage, andwherein the feedback circuit comprises a multiplier whose inputs are connected to the power detector and the signal generator and a comparator for comparing the output of the multiplier with a reference level corresponding to the predetermined power.