Exercise 3.11 Biasing in a radio receiver circuit


An answer:

IC = βfe βfe + 1IE IE = V E R6 V E = V B − V BE V B = V CC ⋅ R4 + R5 R3 + R4 + R5 − IB ⋅(R4 + R5) ⋅ R3 R3 + R4 + R5 ⟹ IC = βfe βfe + 1 V CC ⋅ R4+R5 R3+R4+R5 − 0.6V R6 + 1 βfe+1 ⋅(R4+R5)⋅R3 R3+R4+R5

In this question, letting βfe →∞ from the start:

IC = IE IE = V E R6 V E = V B − V BE V B = V CC ⋅ R4 + R5 R3 + R4 + R5 ⟹ IC = V CC ⋅ R4+R5 R3+R4+R5 − 0.6V R6