The circuit diagram of the TAA 300 is shown in Fig. 20.3. The TAA 300 consists of an input stage (Q1 and Q2), a driver stage (Q3 to Q5) and an output stage (Q6 to Q11). The input stage is a differential amplifier. Since resistor R5 in the common emitters of the differential stage is very large with respect to the differential resistance of the transistors, it can be regarded as a constant current source.

The voltage at the base of Q1 is obtained by means of a low resistance voltage divider across the supply. Resistor R3 between the voltage divider and the base of Q1 increases the input impedance to about 15 KΩ. Two diodes are connected in series with R1 so that the voltage at the base of Q1 does not vary directly ...

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