Chapter 11

Question 1

Why there is a lower voltage swing at the output

Answer 1

Capacitor on output steals some of the signal current and shunts it to ground

Question 2

Inductance

Answer 2

Ls

Question 3

Capacitance

Answer 3

1/Cs

Question 4

If s=0, then H(s) is

Answer 4

DC gain or Ao

Question 5

Narrow bandwidth

Answer 5

Sluggish time response

Noise/fuzziness since it cannot rapidly jump from low to high and spends time in intermediate levels

Question 6

Bode’s Rules

Answer 6

As w passes each pole frequency, the slope decreases by 20dB/dec

As w passes each zero frequency, the slope increases by 20dB/dec

Question 7

Miller multiplication

Answer 7

Capacitor tied between input and output of an inverting amplifier with a gain of Ao raises the input capacitance by (1+Ao)C

Question 8

Capacitors reduce gain when

Answer 8

High frequencies - Low pass

Low frequencies - high pass

Question 9

Cb

Answer 9

To change the collector current, must change the base charge profile by injecting or removing electrons or holes
- non-uniform charge profile so that charge flow from BE to CB junction by diffusion (similar to charging and discharging of capacitor)

Question 10

Cje

Answer 10

BE junction

Question 11

Cmu

Answer 11

BC junction

Question 12

Ccs

Answer 12

Collector-substrate

Question 13

Cpi

Answer 13

Total BE junction

Question 14

Prominent high frequency capacitor in MOSFETs

Answer 14

Due to oxide layer (capacitance between gate and channel Cgs + Cgd)

Between S and Bulk (Csb)

Between D and bulk (Cdb)

Question 15

MOSFET overlap capacitance

Answer 15

Cgs

Cgd

Question 16

Transit frequency

Answer 16

Internal H.F. Capacitors limit the operation model speed of transistors

At high operating speed, H.F. Caps are dominant

Measure of this speed is transit frequency

Question 17

Ft

Answer 17

The frequency at which small signal current gain falls to unity

Question 18

To calculate transit frequency

Answer 18

Inject sinusoidal current into base/gate

Measure resulting collector/drain current

Repeat while frequency increases

Red flag is circuits operating frequency greater than transit frequency

Question 19

Steps to find transfer function

Answer 19

1. Add internal capacitance to schematic
2. Assume band pass response
3. Low frequency
   - open H.F. Caps, leave L.F. Caps as is
   - if signal path method applies, list these poles
   - if not, use KVL
4. High Frequency
   - short L.F. Caps, include H.F. Caps
   - May have to use miller transformation to remove feedback caps
5. Mid-band or pass-band gain
   - open H.F. caps
   - short L.F. caps
   - apply Biasing techniques to find DC gain per circuit configuration
6. Form the transfer function

Question 20

Low pass Characteristics

Answer 20

DC gain

Question 21

Band-pass Characteristics

Answer 21

Passband gain

Question 22

DC gain

Answer 22

Found by opening all caps

Question 23

Passband gain

Answer 23

Open H.F. caps, short L.F. caps

Question 24

High frequency response on cb/Cgd stages

Answer 24

Low input impedance (1/gm)

Does not suffer from miller effect

Question 25

Frequency response of cascode

Answer 25

CE/CS has high input impedance but suffers from miller transformation

CB/CG has no feedback caps but the impedance is low

Cascodes obtain high input impedance with little or no effect from miller transformation