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National Semiconductor
The Monolithic Operational Appendix A A
Amplifier: A Tutorial Study December 1974
Invited PaperÐ It is the intent of this study to develop an understanding for
IEEE Journal of Solid-State Circuits, Vol. SC-9, No. 6 op amp behavior in as direct and intuitive a manner as pos-
AbstractÐA study is made of the integrated circuit opera- sible. This is done by using a variety of simplified circuit
tional amplifier (IC op amp) to explain details of its behavior models which can be analyzed in some cases by inspection,
in a simplified and understandable manner. Included are or in others by writing just a few equations. These simplified
analyses of thermal feedback effects on gain, basic relation- models are generally developed from the single representa-
ships for bandwidth and slew rate, and a discussion of pole- tive op amp configuration shown in Figures 1 and 2.
splitting pensation. Sources of second-order The rationale for starting with the particular circuit of Figure
bandlimiting in the amplifier are also identified and some 1 is based on the following: this circuit contains, in simplified
approaches to speed and bandwidth improvement are de- form, all of the important elements of the monly
veloped. Brief sections are included on new JFETÐbipolar used integrated op amps. It consists essentially of two volt-
circuitry and die area reduction techniques using transcon- age gain stages, an input differential amp and mon
ductance reduction. emitter second stage, followed by a class-AB output emitter
follower which provides low impedance drive to the load.
INTRODUCTION
The two interstages are pensated by a single
The integrated circuit operational amplifier (IC op amp) is small ‘‘pole-splitting’’ capacitor (see below) which is usually
the most widely used of all linear circuits in production to- included on the op amp chip