Part III power amplifier circuits – Class ab

EXAMPLE 4 – Solution (cont’d)

• Since Q4 tends to turn off when vI increases, iB4 is negligible. Therefore;

• Class-AB with Input Buffer Transistors

• POWER AMP

• EXAMPLE 4 – Solution (cont’d)

• The input current;

• The current gain;

• Class-AB with Input Buffer Transistors

• POWER AMP

• EXAMPLE 4 – Solution (cont’d)

• If the previous expression i.e.

• we have;

• is used,

• The higher gain is due the fact that the base currents of Q3 and Q4 are neglected in deriving the expression.

• Class-AB with Input Buffer Transistors

• POWER AMP

• EXERCISES

• Problems 8.36 through 8.38 in the text book