A fast, accurate and digitally calibrate-able logarithmic amplifier for analog predistortion power amplifiers

This paper presents a fast, accurate and digitally calibrate-able logarithmic amplifier (log amp) for an analog predistortion (APD) power amplifier (PA) linearization system. This log amp was designed and fabricated in SiGe BiCMOS 0.35-µm process. Measurement results show that this log amp has over 20 dB input dynamic range with less than ±0.15 dB error over an operating frequency of 0.7 GHz – 2.7 GHz. In addition, its video bandwidth (VBW) is over 64 MHz at all operating conditions, and its response time is 2.2 ns. These results indicate that this logarithmic amplifier is suitable for a fast, accurate AM-AM error detector in applications such as analog predistortion (APD). Furthermore, it can be digitally calibrated, maximizing AM-AM error compensation.