SESSION XV: linear Circuit Techniques - II
N. V. Philips · 1977
THE BASIC PROBLEM in the design of wideband monolithic operational amplifiers is in the provision for adequate bandwidth coupling between the input and output stages without reducing the maximum common mode voltage and output voltage ranges. Frequency compensation is also difficult. Feedback methods cannot be used because an extra phase shift is introduced at unity gain frequencies. An excellent compensation method is to eliminate amplifier stages at high frequenciesl. In the class-B output stage usually used in these amplifiers, there must be no crossover distortion, because it deteriorates the small-signal frequency response. There must also be a low output impedance to reduce the influence of a capacitive load. In this paper a new class-B output stage and a coupling method incorporating the principle of elimination of amplifier stages at high frequencies will be described. All circuits use controlled-current gain transistors to increase performance and decrease chip size. The circuit diagram is given in Figure lfu). It is built up from an NPN-transistor pair (2-1, T3) and a PNP-controlled current source (T2, T4, T5). The connection between the bases of T1 and T3allows for the replacement of T1 by a diode Dl; Figure l(b). The diodes Dl and D3 are connected in series with T2 and T4 respectively, and are found to increase the base emitter