Modified CMOS Op-Amp with Improved Gain and Bandwidth

Mahdi MOTTAGHI-KASHTIBAN
Khayrollah HADIDI
Abdollah KHOEI

Publication
IEICE TRANSACTIONS on Electronics   Vol.E89-C    No.6    pp.775-780
Publication Date: 2006/06/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e89-c.6.775
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit and Device Technologies)
Category: 
Keyword: 
folded cascode,  gain boosting,  bandwidth,  feed-forward compensation,  

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Summary: 
This paper presents a novel gain boosted and bandwidth enhanced CMOS Op-Amp based on the well-known folded cascode structure. In contrast with the conventional methods which increase output resistance for gain boosting, the transconductance of the circuit is increased, therefore the -3 dB frequency is the same as for folded cascode structure. With negligible extra power consumption, the unity gain bandwidth is increased considerably. In this method, a new node is created in the circuit which introduces a pole to the transfer function with a frequency lower than cascode pole; feed-forward compensation is employed to reduce the effect of this pole on the frequency response. The input common mode range is limited slightly by 0.2-0.3 V with respect to folded cascode which is insensible. HSPICE simulations using level 49 parameters (BSIM3v3) in a typical 0.35 µm CMOS technology result in three times gain boosting and 60% enhancement in unity gain bandwidth compared to folded cascode, while the power consumption is increased by 10%.