An Enhanced Scheme of Multi-Stage Amplifier With High-Speed High-Gain Blocks and Recycling Frequency Cascode Circuitry to Improve Gain-Bandwidth and Slew Rate

Po-Yu Kuo,Sheng-Da Tsai

doi:10.1109/access.2019.2940560

Abstract

With the existing circuit topologies, the conventional multi-stage amplifiers (MSA) can only achieve low gain-bandwidths (<;5 MHz) and low slew rates (<;10 V/μs). These specifications are not satisfied by most operational amplifier (OPA) related circuit designers. To solve this issue, a novel enhanced scheme of multi-stage (ESMS) amplifier is proposed by this study. The scheme of the proposed ESMS includes a recycling frequency cascade (RFC) amplifier with a shunt current source and high-speed current mirrors, a high-speed block (HSB), and a high-gain block (HGB). Briefly, the circuitry mechanism of the ESMS amplifier demonstrates two key functions. Firstly, when an input signal is feeding into the first stage, the RFC amplifier along with the shunt current source and the current mirrors, play an important role to enhance the slew rate. Secondly, as the signal goes to the consecutive stage, low and medium frequency signals go through to the direct-coupled high-gain block (HGB), and the high-frequency signal goes to the high-speed block (HSB). Thus, the total DC gain and gain-bandwidth are improved. To test the gain-bandwidth and slew rate characteristics, the proposed ESMS amplifier was simulated by using a TSMC 0.18-μm CMOS process standard technology with a 1.8 V power supply. The results of the experiment showed that when driving a 5-pF/1-kΩ load, the proposed ESMS amplifier achieved 105.5 dB DC gain, 231.77 MHz gain-bandwidth, and 13.25 V/μs average slew rate. Compared to the NMC amplifier, one of the most well-known conventional MSAs, the proposed ESMS amplifier boosted the gain-bandwidth by 55.32 times and improved the average slew rate by 1.55 times.

Highlights

Operational amplifiers (OPAs) are one of the main building blocks in several analog circuits and applications
To enhance the DC gain and slew rate of conventional multi-stage amplifiers, in this paper, we proposed a novel enhanced scheme of multi-stage (ESMS) amplifier
GAIN-BANDWIDTH AND DC GAIN RELATED SPECIFICATIONS PERFORMANCE TESTING To investigate the feasibility of the proposed new ESMS amplifier, its simulated frequency response is compared to the conventional nested-Miller compensation (NMC) amplifier

Summary

INTRODUCTION

Operational amplifiers (OPAs) are one of the main building blocks in several analog circuits and applications. The major proposes of this new ESMS amplifier are to investigate superior gain-bandwidth and good slew rate performances compared to the reported multi-stage amplifiers. The nested-Miller compensation (NMC) was a simple technique that can stabilize multi-stage amplifiers and achieved general improvements in OPA design, as shown in Figure 1 [3]–[5]. The high-speed block (HSB) is composed of a feedforward stage (FFS) and a feedback stage (FBS) connected in series with a compensation capacitor Ca. Besides, the HSB directs the highfrequency signal to the output node, and bypass the low and medium frequency signals through HGB.

The DC gain Adc is given by

CONCLUSION