Inductance

Question 1

What’s another name for an inductor?

Answer 1

Solenoid

Question 2

What does an inductor do?

Answer 2

When a current flows through it, energy is stored in the resulting magnetic field. When the current changes, the time-varying magnetic field induces a voltage in the conductor, which opposes the change in the current that created it.

Question 3

What are some on-chip applications of inductors?

Answer 3

1. Voltage controlled oscillators in Radio Frequency (RF) wireless applications
2. Input matching circuits of low noise amplifiers
3. On-chip chokes (block flow of AC while allowing DC)
4. Inductively loaded pre-amplifiers
5. On-chip transformers

Question 4

What are problems with on-chip inductors?

Answer 4

1. Quality factor (Q) hard to achieve due to limitations in planar process and various design issues.
2. Only able to make inductors with very small values 1-300 nH.

Question 5

What’s the alternative to on-chip inductors?

Answer 5

Off-chip air-wound discrete inductors.

Question 6

What happens to inductance between two wires if their widths change but center points do not move?

Answer 6

Inductance remains constant.

Question 7

What is the equation for inductors in series?

Answer 7

Lab = L1 + L2 + L3

Question 8

What’s the equation for inductors in parallel?

Answer 8

1 / Lab = 1 / L1 + 1 / L2 + 1 / L3

Question 9

What are common styles of planar (monolithic) inductor layouts?

Answer 9

1. Square spirals
2. Octagonal spirals
3. Circular spirals
4. Square symmetric center-tapped

Question 10

What is a “weber”?

Answer 10

Unit of magnetic flux.

Question 11

What is inductance?

Answer 11

Ability of a device to generate magnetic flux by a changing current.

Question 12

What is the definition of 1 Henry?

Answer 12

When you pass 1 amp in 1 second, it will induce 1V on neighbor.

Question 13

Contrast inductors and capacitors.

Answer 13

Inductor blocks changing current, capacitor blocks steady current.