A packaged low-noise high-speed regulated cascode transimpedance amplifier using a 0.6μm N-well CMOS technology

Regulated cascode (RGC) techniques are applied to achieve better isolation of the large input parasitic capacitance in a front-end preamplifier for optical receiver applications, since the RGC circuit behaves like a common-gate transistor with large transconductance comparable to GaAs MESFET. The input resistance of the RGC circuit becomes smaller by the amount of the voltage-gain of the local feedback stage than that of a conventional common-gate input stage. Hence the RGC circuit gives a virtual-ground input impedance and better isolates the input parasitics. With this very low input impedance characteristic, a RGC transimpedance amplifier is realized with a 0.6μm digital CMOS process. This amplifier is packaged in a MQFP package, mounted on a copper PC-board, and housed in an aluminum metal box. The measured results demonstrate 300MHz bandwidth, 57.7dB Ω transimpedance gain, 10 pA/√Hz average noise current spectral density with ±6V power supply.