Multi-stageAMP-compensation-PKT - IEEE TRANSACTIONS ON...

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IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: FUNDAMENTAL THEORY AND APPLICATIONS, VOL. 48, NO. 9, SEPTEMBER 2001 1041 Analysis of Multistage Amplifier–Frequency Compensation Ka Nang Leung and Philip K. T. Mok , Member, IEEE Abstract— Frequency-compensation techniques of single-, two- and three-stage amplifiers based on Miller pole splitting and pole–zero cancellation are reanalyzed. The assumptions made, transfer functions, stability criteria, bandwidths, and important design issues of most of the reported topologies are included. Several proposed methods to improve the published topologies are given. In addition, simulations and experimental results are provided to verify the analysis and to prove the effectiveness of the proposed methods. Index Terms— Damping-factor-control frequency compen- sation, multipath nested Miller compensation, multipath zero cancellation, multistage amplifier, nested Gm-C compensation, nested Miller compensation, simple Miller compensation. I. INTRODUCTION M ULTISTAGE amplifiers are urgently needed with the advance in technologies, due to the fact that single-stage cascode amplifier is no longer suitable in low-voltage designs. Moreover, short-channel effect of the sub-micron CMOS transistor causes output-impedance degradation and hence gain of an amplifier is reduced dramatically. Therefore, many frequency-compensation topologies have been reported to stabilize the multistage amplifiers [1]–[26]. Most of these topologies are based on pole splitting and pole–zero can- cellation using capacitor and resistor. Both analytical and experimental works have been given to prove the effectiveness of these topologies, especially on two-stage Miller compen- sated amplifiers. However, the discussions in some topologies are focused only on the stability criteria, but detailed design information such as some important assumptions are missing. As a result, if the provided stability criteria cannot stabilize the amplifier successfully, circuit designers usually choose the parameters of the compensation network by trial and error and thus optimum compensation cannot be achieved. In fact, there are not many discussions on the comparison of the existing compensation topologies. Therefore, the differences as well as the pros and cons of the topologies should be inves- tigated in detail. This greatly helps the designers in choosing a suitable compensation technique for a particular design condi- tion such as low-power design, variable output capacitance or variable output current. Manuscript received March 9, 2000; revised February 6, 2001. This work was supported by the Research Grant Council of Hong Kong, China under grant HKUST6007/97E. This paper was recommended by Associate Editor N. M. K. Rao.
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Multi-stageAMP-compensation-PKT - IEEE TRANSACTIONS ON...

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