BISMOS Amplifier

BIMOS AMPLIFIER

The common gate amplifier stage is connected in cascade with a common source amplifier stage.

Common Source (CS) Amplifier

i. High Rin

ii. Large transconductance

Common Gate (CG) Amplifier

i. Current buffer

ii. High frequency response

Fig.3.3 shows the BIMOS cascade amplifier. The Common Source (CS) transistor Q₁ conducts a current signal due to input signal voltage V_i.

The output in its drain terminal is fed to the source of Common Gate (CG) transistor Q₂. The output of Q₂ is sent to its drain and the load R_L.

Q₂ transistor acts as a buffer, offering low input impedance to Q₁ drain and high impedance at output.

Fig.3.4 shows the combination of both BJT and FET in cascode operation.

MOSFET provides an infinite input resistance, while BJT provides larger output resistance.

BJT CB transistor provides lower R_in than CG transistor, thus reducing Miller effect in Q₁.

FET CASCADE AMPLIFIER

Fig.3.5 shows the circuit of two common source (CS) amplifier stages connected in cascade.

Stage 1:

Stage 2:

Cascaded Amplifier

The overall parameters of the cascaded two stage amplifier are