# Can anyone please explain the difference between DC bias field versus AC bias field ?

#### nckt

Joined Oct 25, 2021
3
What is DC and AC bias? Are these two applied together to a circuit ? Also what is DC bias field ?

#### Papabravo

Joined Feb 24, 2006
17,605
What is DC and AC bias? Are these two applied together to a circuit ? Also what is DC bias field ?
I've never heard of a DC bias field. Can you provide some context?

A circuit can be subjected to two different types of analysis. A DC analysis is where each point in a circuit has a defined and constant DC value This analysis establishes the DC operating point. A constant DC value in between a power supply value and ground is referred to as a DC bias (value). It is often constructed with a pair of resistors called a voltage divider. Once the DC operating point is established then a small signal AC analysis can be performed by looking at small signal deviations from the DC operating point.

I don't know that the term AC bias has any useful interpretation. If it does it's above my pay grade.

#### AlbertHall

Joined Jun 4, 2014
11,700

#### Papabravo

Joined Feb 24, 2006
17,605
These terms used to be applied to audio tape recording to reduce distortion caused by the non-linear magnetic response of the replay head.
https://en.wikipedia.org/wiki/Tape_bias
I never did know anything about audio tape recording. Too many subjects -- too little time.

#### MrChips

Joined Oct 2, 2009
25,040
What is DC and AC bias? Are these two applied together to a circuit ? Also what is DC bias field ?
It would help if you told us the context to which this is applied.

#### Audioguru again

Joined Oct 21, 2019
4,129

#### nckt

Joined Oct 25, 2021
3
It would help if you told us the context to which this is applied.
Hi MrChips, I first came across the DC bias field reading a research paper. The text contained :

The photoconductive antenna consists of a DC biased metal dipole antenna patterned on a photoconductive substrate. The optical pulse is incident on the antenna gap (G), propagates into the photoconductor, and begins to generate photocarriers inside the photoconductor. The generated photocarriers are accelerated in the DC bias field, producing a transient photocurrent, which drives the dipole antenna.

I would have thought it is just the usual electric field as a result of DC bias. But I am not 100% sure.

Once I agonised over DC bias, I started thinking about AC bias and came across a "tape recording wiki article" shared by @AlbertHall. Now I am even more confused about the output and application of these two.

#### nckt

Joined Oct 25, 2021
3
I've never heard of a DC bias field. Can you provide some context?

A circuit can be subjected to two different types of analysis. A DC analysis is where each point in a circuit has a defined and constant DC value This analysis establishes the DC operating point. A constant DC value in between a power supply value and ground is referred to as a DC bias (value). It is often constructed with a pair of resistors called a voltage divider. Once the DC operating point is established then a small signal AC analysis can be performed by looking at small signal deviations from the DC operating point.

I don't know that the term AC bias has any useful interpretation. If it does it's above my pay grade.
The context for the DC bias field is from a research paper that mentioned the following :

The photoconductive antenna consists of a DC biased metal dipole antenna patterned on a photoconductive substrate. The optical pulse is incident on the antenna gap (G), propagates into the photoconductor, and begins to generate photocarriers inside the photoconductor. The generated photocarriers are accelerated in the DC bias field, producing a transient photocurrent, which drives the dipole antenna.

I thought it is just a normal electric field but not sure! Like eg AC bias, I didn't realise it is used for tape recording until I pondered on the term "bias".

#### AlbertHall

Joined Jun 4, 2014
11,700
Nope, not replay. AC bias was used for tape recording.
Correct, and so was DC bias.

#### MrChips

Joined Oct 2, 2009
25,040
According to the paper, there is no AC bias field involved.
Hence a DC bias field refers to a constant voltage applied between two conducting material separated by an insulating material.

#### Ramussons

Joined May 3, 2013
1,154
The only area I know of, where both AC and DC bias are discussed is Magnetic Recording.

#### MisterBill2

Joined Jan 23, 2018
10,572
Everybody: go back and read post #7! It sounds a whole lot like the desription of a high speed photodiode being driven by a light source to create an RF signal fed to an antenna. An interesting way to avoid transmission line losses. but not likely to produce a whole lot of power.

#### Danko

Joined Nov 22, 2017
1,203