Self Assessment Quiz

Lecture 8 :- Cascode Amplifiers

Common Data : VDD = 1.8V , Lmin  = 0.18µm, µ0N = 350cm2/V s, µ0P  = 100cm2/V s, |VTH | = 0.55, tox = 3.8nm, λ = 0.07V−1, χ = 0.1.

1. Design Cascode amplifier (Fig. 7 ) for a gain AV > −50V /V , V outmax of 1.3V, V outmin of 0.4V. The slew rate with 5pF load should be at least 10V /µsec. Supply voltage is 1.8V and maximum power dissipation is 200µW .

Figure 7: Figure for Question 1

2. Calculate the transconductance and output resistance of the cascode circuit shown in Fig. 8 . Assume both transistors are in saturation and gm = 2mA/V and r0 = 20kΩ. Ignore body effect. Repeat the calculation including body effect and observe the percentage of error.

Figure 8: Figure for Question 2

3. Calculate the output impedance of the circuit shown in Fig. 9 and state the advantages and disadvantages of the circuit.

Figure 9: Figure for Question 3

4. Find the output resistance for the active cascode circuit shown in Fig.  10 excluding resistor R. What is the maximum allowable output swing?

Figure 10: Figure for Question 4

5. Determine input resistance, transconductance, output resistance and maximum open circuit voltage gain of cascode if ID = 300µA, W/L = 200.

Figure 11: Figure for Question 5

6. Consider the cascode amplifier shown in Fig. 12. Given gm1 = 1mA/V , gm2 = 0.5mA/V , calculate the gain of the amplifier and the swing on node X. Ignore channel length modulation and body effect.

Figure. 6 Circuit for Q6