Wideband Amplifier Design Using Major Multiloop Feedback Techniques

Wideband feedback amplifier design has heretofore mainly been accomplished by the use of single major loop feedback techniques. 1-4 Major loop feedback implies t h a t the current or voltage on the input to the basic amplifying element is manipulated by the current or voltage that appears 011 the output of the basic amplifying element. The design concept follows the classical feedback design procedure of assuming a unilateral forward amplifying element of voltage gain n and a feedback path with voltage gain fi. Existing multiloop feedback techniques have been primarily concerned with stability considerations of " t a n d e m " 5 and minor multiloop 2 ' 3 feedback arrangements. In many applications, input and output impedance matching of the amplifier is necessary. The communications amplifier is one such example, since it requires very low levels of signal interference due to input or output impedance mismatch. The classical single-loop feedback techniques offer little help in designing for the impedance matching constraint. This is due to the fact t h a t the more loop gain in a single-loop feedback circuit, the more extreme (zero or infinite) the input and output impedance becomes. 1-3 Two techniques that are 1253