Nested-Current-Mirror Rail-to-Rail-Output Single-Stage Amplifier With Enhancements of DC Gain, GBW and Slew Rate

For better area and power efficiencies, rail-to-rail-output single-stage amplifiers are a potential replacement of their multi-stage counterparts, especially for display applications that entail massive buffer amplifiers in their column drivers. This paper describes a nested-current-mirror (NCM) technique for a single-stage amplifier to achieve substantial enhancements of DC gain, gain-bandwidth product (GBW) and slew rate (SR). Specifically, NCM is customizable for different mirror steps, and sub mirror ratios, to balance the performance metrics and capacitive-load ( CL) drivability, avoiding any compensation passives while preserving a rail-to-rail output swing. Analytical treatments of the NCM technique in terms of performance limits and robustness reveal that the NCM amplifier can surpass the fundamental power-efficiency limit set by the basic differential-pair (DP) amplifier. Two prototypes, 3-step and 4-step NCM amplifiers, were fabricated in 0.18 μm CMOS for systematic comparison with the DP amplifier. The former represents a robust design exhibiting 72 dB DC gain and 0.0028-0.27 MHz GBW over 0.15-15 nF CL with 80 ° phase margin (PM). The latter embodies an aggressive design attaining 84 dB DC gain and 0.013-1.24 MHz GBW over 0.15-15 nF CL with 62 ° PM. All amplifiers were sized for the same area (0.0013 mm 2) and power (3.6 μW).