Thursday, May 17, 2012

Distributed Bidirectional Amplifiers in CMOS

This research was conducted along with Dr. Ziad El-Khatib as part of his Ph.D. program. From Ziad's abstract:

A highly-linear transmitter with fully-integrated broadband design linearization capabil- ity is required to address linearity improvements. When the input signal driven into the amplifier semiconductor is increased, the output is also increased until a point where dis- tortion products can no longer be ignored. The harmonics and higher order distortion of the output signal are generated by nonlinearities of MOSFET devices. In response to the need to correct the broadband distributed amplifier (DA)’s nonlinear distortion, a num- ber of DA linearization techniques have been developed. However, most of the published DA linearization methods reported do not provide fully-integrated distortion cancellation techniques with large third-order intermodulation (IM3) distortion reduction.

The main contributions of this thesis research is the realization a fully-integrated high- frequency active broadband linearizer for large IM3 distortion cancellation and spectral regrowth reduction in standard CMOS technology.

In this thesis, we demonstrate a fully-integrated fully-differential linearized CMOS dis- tributed bidirectional amplifier that achieves large IMD3 distortion reduction over broad- band frequency range for both RF paths. The proposed linearized bidirectional DA has the drain and gate transmission-lines stagger-compensated. Reducing the DA IM3 distortion by mismatching the gate and drain LC delay-line ladders. The proposed fully-differential linearized DA employs a cross-coupled compensator transconductor to enhance the linearity of the DA gain cell with a nonlinear drain capacitance compensator for wider linearization bandwidth. The proposed linearized CMOS bidirectional DA achieves a measured IM3 distortion reduction of 20 dB with frequency of operation from 0.1 GHz to 9.5 GHz and a two-way amplification of 5 dB in both RF directions. The proposed linearized DA is imple- mented in 0.13μm RF CMOS process for use in highly-linear broadband communication.