The Sixteen Faces of Feedback: A Catalogue of the Basic Negative Feedback Amplifier Configurations

Classical feedback literature refers to series and shunt feedback or voltage and current feedback, implying only two feedback configurations which may be employed with an amplifier. Actually there are four separate configurations: 1) voltage sensed at output and voltage returned to input, 2) voltage sensed at output and current returned to input, 3) current sensed at output and voltage returned to input, and 4) current sensed at output and current returned to input. Also, if we examine the amplifier around which such feedback is utilized, we see the existence of four ideal transfer functions: 1) voltage amplifier, 2) current amplifier, 3) transimpedance amplifier, and 4) transadmittance amplifier. If we consider the employment of each of the four basic feedback types around each of the four basic amplifier types, we have a total of sixteen different configurations. This paper discusses the effect of the negative feedback in each of these sixteen cases. In general, the closed-loop transfer function approximates the reciprocal of the feedback network transfer function so that any one of the four types of amplifiers may be transfonned (with the proper choice of feedback) into any of the three other basic types, or into an improved version of the same type.