Amplifier gain enhancement with positive feedback

The use of positive feedback as a solution to maximum intrinsic gain degradation in scaled technologies is discussed. Criteria for increasing gain while keeping the system stable are derived in terms of a non-ideal amplifier model. The amplifier model, in an attempt to standardize positive feedback analysis on generic amplifiers, includes non idealities that traditional feedback theory does not, including finite input impedance and non-zero output impedance. This treatment shows that as amplifier open loop gain decreases, positive feedback can more readily be applied to increase that gain at a cost of a slightly more than one-to-one tradeoff with the amplifier bandwidth and minimal area overhead. This analysis shows that the concept of positive feedback is most useful in high bandwidth single stage amplifiers where gain is at a minimum. The theory is applied to a differential amplifier in 65 nm technology and is shown to increase the DC gain by more than 25 dB in silicon measurements.

[1]  P.R. Mukund,et al.  Using positive feedback to overcome gmro limitations in scaled CMOS amplifier design , 2008, 2008 51st Midwest Symposium on Circuits and Systems.

[2]  J. Burleson,et al.  Maximum intrinsic gain degradation in technology scaling , 2007, 2007 International Semiconductor Device Research Symposium.

[3]  Anne-Johan Annema,et al.  Analog circuit performance and process scaling , 1999 .

[4]  B. Nauta,et al.  Analog circuits in ultra-deep-submicron CMOS , 2005, IEEE Journal of Solid-State Circuits.

[5]  T.S. Kalkur,et al.  High-speed current-mode logic amplifier using positive feedback and feed-forward source-follower techniques for high-speed CMOS I/O buffer , 2005, IEEE Journal of Solid-State Circuits.

[6]  Randall L. Geiger,et al.  A high gain strategy with positive-feedback gain enhancement technique , 2001, ISCAS 2001. The 2001 IEEE International Symposium on Circuits and Systems (Cat. No.01CH37196).

[7]  Randall L. Geiger,et al.  Positive feedback gain-enhancement techniques for amplifier design , 2002, 2002 IEEE International Symposium on Circuits and Systems. Proceedings (Cat. No.02CH37353).