Gain-Bandwidth Enhancement in Folded-Cascode Op-Amp

A compensated high gain-bandwidth amplifier is the main block in structures with negative feedback. At high frequencies, open-loop gain drops, decreasing feedback loop-gain and affecting system performance dramatically. While the cascaded gain stages are not suggested due to their compensation difficulties, cascode structures such as telescopic cascode op-amps are recommended. Considering high-swing output voltage, the folded-cascode is one of the most common methods rather than telescopic structure. Some other methods such as positive feedback are used to increase gain but this method improves only the DC gain while the gain-bandwidth remains constant eventually, moreover stability problems arise. In this paper, a novel method is proposed in order to increase gain-bandwidth of the folded-cascode op-amp in 0.35μm (Vdd=3.3v) standard CMOS technology. In addition, some of the side effects are discussed such as the transconductance linearity improvement. Simulation results confirm that in tradeoff between bandwidth and power consumption, both sides are improved by 30% and 60%, respectively.

Keywords:

folded cascode , gain bandwidth , gain , feedback , amplifier