Design of a CMOS Broadband Transimpedance Amplifier With Active Feedback

In this paper, a novel current-mode transimpedance amplifier (TIA) exploiting the common gate input stage with common source active feedback has been realized in CHRT 0.18 mu m-1.8 V RFCMOS technology. The proposed active feedback TIA input stage is able to achieve a low input impedance similar to that of the well-known regulated cascode (RGC) topology. The proposed TIA also employs series inductive peaking and capacitive degeneration techniques to enhance the bandwidth and the gain. The measured transimpedance gain is 54.6 dB Omega with a 3 dB bandwidth of about 7 GHz for a total input parasitic capacitance of 0.3 pF. The measured average input referred noise current spectral density is about 17.5 pA/ root Hz up to 7 GHz. The measured group delay is within 65 +/- 10 ps over the bandwidth of interest. The chip consumes 18.6 mW DC power from a single 1.8 V supply. The mathematical analysis of the proposed TIA is presented together with a detailed noise analysis based on the van der Ziel MOSFET noise model. The effect of the induced gate noise in a broadband TIA is included.