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.