Is it possible to amplify uniforn current?

[aekanshchumber]

Hello,
Will please anyone help me out of this, i want to know that can a uniform current no matter a.c or d.c be amplified. I am working on a experiment in which the current which will e induced by a photodiode will have to be amplified. I know that we can amplify A.C using transformers also amplification is also done in a t.v set.
But the probem is we know that signals in both the transformer and t.v set are not uniform but in this experiment we do not know that will current indused will be uniform or non-uniform as it all depend on the frequency of the light and its intensity at the moment.
any kind of help is really appreciated.
Thanx.

 

[pervect]

Hello,
Will please anyone help me out of this, i want to know that can a uniform current no matter a.c or d.c be amplified. I am working on a experiment in which the current which will e induced by a photodiode will have to be amplified. I know that we can amplify A.C using transformers also amplification is also done in a t.v set.
But the probem is we know that signals in both the transformer and t.v set are not uniform but in this experiment we do not know that will current indused will be uniform or non-uniform as it all depend on the frequency of the light and its intensity at the moment.
any kind of help is really appreciated.
Thanx.

You can amplify uniform currents, but in general you will have problems with extremely high gains in doing this, due to offset problems. This means that zero current in will tend to produce some signal that is not zero, due to imperfections in the amplifier, if the gain is high enough. Furthermore, the signal so produced will tend to "drift" with time.

I think the best circuits for this are still operational amplifiers - the high priced high performance version of these are called instrumentation amplifiers

I think a standard current-voltage conversion would be your best bet offhand, connect one end of the photodiode to a bias voltage, the other side of the photodiode to the negative terminal of an op amp/ instrumentation amplifier, and connect a resistor from the output of the op amp to the negative terminal. The positive terminal of the op amp goes to a reference signal / ground. (Usually you need positive and negative supplies for an op amp circuit).


The gain of the circuit will be set by the value of the resistor, i.e. the output current will be the photodiode current times the value of the resistor.

http://ezphysics.nchu.edu.tw/prophys/ael/File/Datasheet/AD648JQ.pdf

has, if you look far enough, a "dual photodiode" amplifier, you just want 1/2 of that circuit.

I really don't know much about the specific op-amp discussed in the data sheet, there may be better ones for your purpose, though it is promising that your application is discussed. The input current and offset voltage look quite low - OTOH it may be pricey, usually good specs come at a high price.

I don't quite understand what you're trying to accomplish. If you run into too many problems with the DC coupled approach, you may have to resort to AC coupling, even if you don't want to.

You might consider moving this thread to the electrical engineering section of the board as well...