A novel transimpedance amplifier with variable gain

In this paper we propose a variable-gain transimpedance amplifier suitable for low-power applications. Its noise, bandwidth and input impedance performance are similar to a more conventional regulated-cascode common-gate transimpedance with resistive load, with the same power consumption and gain performance. The proposed amplifier has, however, variable gain, which can be easily changed by setting a control voltage. Besides, it uses no passive components and can thus occupy less space in the layout, a feature of interest in applications which require the use of many sensors. With 30µW dissipation, it achieves 800MHz performance with 50fF input and output loads, in a 65nm CMOS technology. The transimpedance gain is 68dB, and the input impedance is 180Ω.