An Analog On-Line Gain Calibration Loop for RF Amplifiers

This paper presents an analog on-line gain calibration loop for radio-frequency (RF) amplifiers. In the proposed calibration scheme, the gain of an RF amplifier is determined by programmable resistor ratios of two transimpedance amplifiers (TIAs), while the corresponding control voltage is generated through a differential difference amplifier (DDA). Being the first work to propose a continuous-time gain calibration technique for RF amplifiers, the loop dynamics such as settling time, stability and control voltage ripples are analyzed by means of mathematical modeling of each circuit building block. As a result, a systematic design procedure is developed. In order to validate the concept, a 5.2-GHz variable-gain low-noise amplifier (LNA) is integrated with the proposed analog gain calibration loop for demonstration. By using a standard 0.18- μm CMOS process, the fabricated circuit consumes a total dc power of 18.5 mW from a 1.8-V supply, while the measured maximum gain error is less than 1 dB.