Common Source Amplifier (Biased by Current Source)

ESE 372 / Spring 2013 / Lecture 21 Common Source Amplifier (biased by current source)

1 ESE 372 / Spring 2013 / Lecture 21

Common Source Amplifier with RSS (improves dynamic range)

2 ESE 372 / Spring 2013 / Lecture 21 Common Gate Amplifier (biased by current source)

3 ESE 372 / Spring 2013 / Lecture 21 Common Drain Amplifier (biased by current source)

4 ESE 372 / Spring 2013 / Lecture 21 MOSFET model with capacitances

5 ESE 372 / Spring 2013 / Lecture 21 Unity gain frequency/bandwidth

6 ESE 372 / Spring 2013 / Lecture 21 Frequency response of CS amplifier

7 ESE 372 / Spring 2013 / Lecture 21

Low frequency cutoff fL

8 ESE 372 / Spring 2013 / Lecture 21

High frequency cutoff fH

9 ESE 372 / Spring 2013 / Lecture 21 Miller Transformation

Equivalent circuit

10 ESE 372 / Spring 2013 / Lecture 21 Miller Transformation in CS amplifier

Equivalent circuit

11 ESE 372 / Spring 2013 / Lecture 21 Another way of looking at it –open circuit time constants.

The high frequency 3dB cutoff can be estimated as:

Open circuit time constants corresponding to each capacitor in the small signal equivalent circuit:

12 ESE 372 / Spring 2013 / Lecture 21 Another way of looking at it –open circuit time constants.

13 ESE 372 / Spring 2013 / Lecture 21 Common Gate Amplifier

Moderate freq. equivalent circuit

14 ESE 372 / Spring 2013 / Lecture 21 Common Gate Amplifier

15 ESE 372 / Spring 2013 / Lecture 21 High frequency cut‐off of CS amplifier with capacitive load

16 ESE 372 / Spring 2013 / Lecture 21 Capacitive load and open circuit time constants

LPF at the output due to capacitive load dominates.

We need voltage buffer to deal with CL

17 ESE 372 / Spring 2013 / Lecture 21 Common Drain Amplifier with capacitive load

Low/Moderate ffqreq. equivalent circuit

18 ESE 372 / Spring 2013 / Lecture 21 Common Drain Amplifier with capacitive load

19 ESE 372 / Spring 2013 / Lecture 21 Basic concept of tuned amplifier