Multistage amplifier topologies with nested G/sub m/-C compensation

This paper presents a multistage amplifier for low-voltage applications (<2 V). The amplifier consists of simple (noncascode) low gain stages and is stabilized using a nested transconductance-capacitance compensation (NGCC) scheme. The resulting topology is similar to the well known nested Miller compensation (NMC) multistage amplifier, except that the proposed topology contains extra G/sub m/ feedforward stages which are used to enhance the amplifier performance. The NGCC simplifies the transfer function of the proposed multistage amplifier which, in turn, simplifies its stability conditions. A comparison between the NGCC and NMC shows that the NGCC has wider bandwidth and is easier to stabilize. A four-stage NGCC amplifier has been fabricated using a 2-/spl mu/m CMOS process and is tested using a /spl plusmn/1.0 V power supply. A dc gain of 100 dB has been measured. A gain bandwidth product of 1 MHz with 58/spl deg/ of phase margin and power of 1.4 mW can be achieved. The op amp occupies an active area of 0.22 mm/sup 2/. Step response shows that the op amp is stable.