Temperature compensated logarithmic peak detector

A temperature compensated logarithmic amplifier for signal strength indicator or automatic gain control applications is presented. The logarithmic function is realized with a current-feedback operational amplifier with a nonlinear diode feedback. The designed BiCMOS current-feedback operational amplifier utilizes a novel circuit topology which makes possible constant 1 MHz bandwidth amplification with closed loop voltage gains up to 60 dB. The offset current of the current-feedback amplifier is cancelled with an active OTA-C feedback loop. The logarithmically amplified signal is further processed by a peak detector and a temperature compensation circuit. The temperature compensation principle is based on a division of two v _BE:s and it is realized with a current controlled variable current mirror. The logarithmic amplifier is fabricated with a 1.2 micron BiCMOS-process with NPN's f_T of 7 GHz. The power consumption of the circuit is 25 mW with a 4.5 V supply voltage.