2

Question 1

Width of p channel twice width of nchannel to match.

Question 2

Always some resistance in mosfets

Question 3

On Resistance (R_on) has to be matched between n channel and p channel, although practically they differ very slightly.

Answer 3

(a few microohms for example)

Question 4

Why is it important to match R_on for both PUN and PDN?

Answer 4

If load is modeled as capacitor and resistor in parallel, resistor from mosfet acts as a low pass filter and no longer a digital circuit. Rise time is slower due to this filter. Instead a square wave, a distorted wave it happening.

Question 5

Mosfets have some capacitance that is not idea

Answer 5

Leaky capacitance.

Question 6

Reason our processors aren’t getting much faster.

Answer 6

Ron cant get much smaller due to capacitance. Instead we make parallel processors.

Question 7

How can you reduce R_on?

Answer 7

Increase width of transistors. There is a tradeoff between space effectiveness and speed.

Question 8

Although Decreasing Ron also increases capacitance.

Question 9

Via contact

Answer 9

Metal vertical connector on mosfets.

Question 10

New technologies have up to 40 via layers. Most have about 4 layers.

Question 11

VDD is only connected to one via ontop and to the other to the side to avoid short circuiting.

Question 12

Visual cortex in brain takes lots of volume such as graphics sl chips take up lots of semiconductor chips.

Question 13

Stick diagram ignores substrate connection on mosfet.

Question 14

Threshold voltage variation occurs if substrate of B parallel mosfet gets shorted if not connected to VDD like in A.

Question 15

Why do we need nwell

Answer 15

Acts as substrate for p channel transistor. If nwell wasn’t there p+ will short circuit with other p in other transistor.

Question 16

Depletion region acts as

Answer 16

Insulator.

Question 17

Why is there an overlap in the gate metal connection in stick diagrams?

Answer 17

Misalignment issue while manufacturing. (Mask) sometimes there might not be a total connection if it’s flush.

Question 18

Manufactures will give spacing rules or guidelines for their manufacturing of your circuits that as designers we need to consider named this.

Answer 18

Lamba rules

Question 19

What is lamba in lamda rules?

Answer 19

Lamda = length (L) / 2.

Question 20

Why do we need lamba rules

Answer 20

Accuracy of manufacturing process, but also two metals form a capacitance and need some distance to be sufficiently small.

Question 21

What is Tristate not gate?

Answer 21

A not gate with an extra pmos and extra nmos in series with enable inputs.

Question 22

IIIE1164 Logic levels consists of how many levels?

Answer 22

9, although we only consider a few:

Strong 1
Strong 0
H (weak 1)
L (weak 0)
Z high impedence.
Don’t care

Question 23

What makes a strong logic signal

Answer 23

Typically Resistance around 0 in thevenin equivalent (or less than equal 10 ohms)

Question 24

What consists of a weak logic gate

Answer 24

Higher Ron resistance from about 10-100 ohms.

Question 25

What consists of high impedence logic circuit.

Answer 25

Resistance is so high that it it basically an open circuit.

Question 26

What are parasitic capacitors?

Answer 26

A mosfter (4 terminal device Gate, drain source, substrate) with a capacitor in between all nodes.