TerryCFBamp

TerryCFBamp - IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL....

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IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-15, NO. 2, APRIL 1980 155 The Use of Current Amplifiers for High Performance Voltage Applications PHILLIP E. ALLEN, MEMBER, IEEE, AND MICHAEL B. TERRY Abstract–A current amplifier is used to realize a voltage amplifier having an improved high frequency response and slew rate capability. It is shown that the closed loop bandwidth is independent of the closed loop voltage gain. The design and application of a unity gain and a high gain current amplifier to voltage signal processing circuits are given. The results demonstrate an efficient use of the inherent frequency response capabilities of the active devices in the circuit to achieve the amplifica- tion of high frequency and large amplitude voItage signals. INTRODUCTION I T has become customary in electrical engineering to think of signal processing in terms of voltage variables rather than current variables. This tendency has resulted in voltage signal processing circuits such as voltage amplifiers, voltage integra- tors, filters which realize a voltage transfer function, etc. Most analog signal processing is accomplished through the use of feedback around a high gain voltage amplifier to achieve a well defined voltage transfer function which is independent of the active devices. The high gain voltage amplifier may consist of discrete components or maybe an integrated circuit such as an operational amplifier. This approach has worked well as evi- denced by a large number of analog circuits which use the operational amplifier. Unfortunately, the voltage controlled voltage source (VCVS) operational amplifier has several limita- tions which prevent high performance operation. One of these limitations is that the product of the closed loop -3 dB band- width and the closed loop voltage gain is approximately a constant [1]. Thus for a typical internally compensated oper- ational amplifier the closed loop -3 dB bandwidth decreases as the closed loop voltage gain increases. Another serious limita- tion of the internally compensated VCVS operational ampli- fier can be its typically low voltage slew rate [2]. In order to be compatible with voltage signal processing circuits, it is desirable to keep the closed loop, input, and out- put variables of an analog signal processing circuit as voltage variables. However, it is not necessary to use high gain voltage amplifiers in the feedback configuration to accomplish this end. Other types of operational amplifiers besides the VCVS type presently exist and are used in analog circuits [3] - [5]. Unfortunately, these non-VCVS operational amplifiers have Manuscript received April 25, 1979; revised August 3, 1979. P. E. Allen is with the Department of Electrical Engineering, Texas A&M University, College Station, TX 77843.
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TerryCFBamp - IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL....

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