A low-voltage CMOS current-mode differential front-end for optical communications

This thesis deals with the design of a low-voltage fully-differential CMOS current-mode preamplifier for optical communications. An in-depth comparative analysis of the building blocks of low-voltage CMOS current-mode circuits is carried out. Two new bandwidth enhancement techniques, namely inductor series-peaking and current feedback, are introduced and implemented in the design. The feedback also reduces the value of the series-peaking inductor. The minimum supply voltage of the amplifier is only one threshold voltage plus one pinch-off voltage. The preamplifier has a balanced differential topology such that the effect of bias dependent mismatches is minimized and the amplifier is insensitive to the switching noise caused by the digital circuitry. Negative differential current feedbacks are implemented to boost the bandwidth and increase the dynamic range.