Using External Feedback To Achieve Flat Gain

56 EE March 1989 The contents of this column are based on information obtained from manufacturers in the electronics industry, or their representatives, and do not imply practical experience by Elektor Electronics or its consultants. USING EXTERNAL FEEDBACK TO ACHIEVE FLAT GAIN Introduction One of the classic problems facing the r.f. designer is to build a cascadable am- plification stage that has flat power gain over a broad frequency range. The diffi- culties arise from the gain vs frequency characteristics of semiconductor devices. Up to some frequency ff3 transistors ex- hibit flat gain vs frequency performance. Above fp the gain of the transistor will drop at rate of 6 dB per octave (i.e. the amplification factor will decrease by "A for each doubling in frequency.) Since f is a relatively low frequency (300 MHz typically for Avantek"s SAT bipolar pro- cess) the designer is usually working in this area of gain rolloff. Thus a "per- fectly matched" amplifier (an amplifier with ...