Comparison of the Frequency Compensation Techniques for CMOS Two-Stage Miller OTAs

Several design options are nowadays available for the frequency compensation of CMOS two-stage transconductance operational amplifiers, from the traditional Miller approach employing a nulling resistor or a voltage buffer, to a current buffer or the more modern current amplifier. However, designers have no results on the frequency performance achievable that allow to consciously choose the best approach to meet the prescribed specifications efficiently. In this paper, a comparison among the possible Miller approaches is carried out by exploiting an analytical figure of merit that expresses a tradeoff between gain--bandwidth product, load capacitance, and total transconductance for a given value of phase margin. Interesting and useful results, even unexpected, are found. The accuracy of the comparison is also validated through simulations.