Closed loop transmitter with dac sensitivity adjusted to detector nonlinearity

Abstract

A power control circuit for use with a closed loop transmitter such as a cellular telephone. The inventive circuit includes a first element for providing a transmitter output signal. A second element serves to receive a power level signal. A third element is included for adjusting the transmitter output signal in response to the power level signal in accordance with a first scale factor over a first range if the power level signal is below a first threshold and for adjusting the transmitter output signal in response to the power level signal in accordance with a second scale factor over a second range if the power level signal is not below the first threshold. In the illustrative embodiment, the system is adapted for use in a mobile station of a cellular telephone system to which a power level control signal is supplied by a base station thereof. The first element is a variable gain amplifier, the second element is a microprocessor. The third element includes a digital-to-analog converter, a detector for detecting a peak amplitude of the output, a subtractor for subtracting the output of the detector from a reference voltage. The reference voltage is supplied by the digital-to-analog converter. The output of the subtractor is input to a variable gain control input of the variable gain amplifier. The invention affords an improved design for a cellular telephone transmitter including a modulator for upconverting in input signal; a variable gain amplifier, a feedback loop coupled to the output of the amplifier and a gain varying input thereof and a circuit for adjusting the response of the feedback loop in response to changes in an applied control voltage.