RF Electronics Chapter 2: Computer Simulation Page 17
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 2.17. Bias stabilisation of Transistor amplifiers.
Figure 2.17 shows three transistor circuits that are often used to demonstrate bias
stabilisation. The left circuit uses no bias stabilisation, the middle circuit uses collector
bias stabilisation and the right circuit used emitter bias stabilisation. These circuits all use
the Hybrid Pi transistor model of figure 2.16. The effect of changing the transistor gain
Beta can be investigated by selecting Simulate Tune, and then vary Beta and to
observe the effect of the changes. In addition, the input voltage can be changed and the
resulting change in output can be seen.
Bipolar Transistor (Closed Form): BIP
Symbol Equivalent Circuit
Parameters
Figure 2.18. BIP circuit of the closed form transistor model from AWR DE [10].
Since the Hybrid, Pi or T models are linear AC only models; DC voltages, bias stability
or clipping of the amplifier cannot be observed. The manufacturers data sheet [11] for the
BC546 BJT transistor, gives Ccb = 1.7 pF and Cbe = 10 pF. Using those values in figure
2.16 results in a similar frequency response to that obtained in figure 2.24.
RF Electronics: Design and Simulation
17 www.cadence.com/go/awr
