The TAA320 is a monolithic integrated circuit comprising three components mounted in a T0–18 envelope: a MOS transistor of the p-channel enhancement type, an npn silicon transistor and a resistor. Its circuit is given in Fig. 20.6.
The biasing resistor R adjusts the operating current, Is, of the MOS transistor. Since its transconductance is proportional to Is, resistor R must be as small as possible to obtain maximum gain; on the other hand a low value reduces amplification of the silicon transistor. A value of about 1 KΩ gives optimum overall transconductance of the whole integrated circuit.
The TAA320 has advantages in that it combines a high transconductance with a high input impedance and low noise level.