Multistage amplifier topologies with nested G -C compensation

Abstract — 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 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-m CMOS process and is tested using a 1.0 V power supply. A dc gain of 100 dB has been measured. A gain bandwidth product of 1 MHz with 58 of phase margin and power of 1.4 mW can be achieved. The op amp occupies an active area of 0.22 mm2. Step response shows that the op amp is stable. Index Terms—Amplifiers, compensation, multistage amplifiers, operational amplifiers. I