A Self-Calibrated Power Detector and Current Sensor for Use in a Power Amplifier Control Circuit

Abstract

The power amplifier in a transmitter, especially high-power transmitters, generally uses more power than any other component in the signal chain. As a result, large power savings can be achieved if the efficiency of the power amplifier is optimized. Additionally, power amplifiers in high-power transmitters generally experience substantial amounts of reliability-reducing stress such as high temperature operation. Given these considerations, a power amplifier control loop is proposed which will calculate various parameters of the amplifier, such as the power-added efficiency. This control loop will then adjust the input power and DC bias current of the power amplifier to maximize the efficiency while also ensuing the amplifier is not placed in a situation where its reliability is compromised. This thesis will discuss the design of two major blocks that are required in this control loop: a DC bias current sensor and a power detector.

The DC bias current sensor must accurately measure the DC bias of the power amplifier since this current is used to calculate the DC power dissipation for the power-added efficiency. In order to ensure the DC current sensor’s output is accurate over a wide temperature range, a reference current calibration scheme is introduced. The fabricated current sensor is able to achieve a measurement accuracy of +/-1% over a current range from 100mA to 4A.

The power detector must measure the input and output power of the power amplifier since the power added efficiency takes into account the gain of the amplifier. The proposed power detector utilizes an on-chip reference generator in order to calibrate the peak detector used and provide an accurate and absolute power level. The simulated power detector is able to provide an accuracy of +/-0.5dB over a dynamic range of 40dB. These two designs will be incorporated in the overall power amplifier control system in future work.