Recent content by PhysicsGuy99

The input current I require is order of 10-100mA. Well outside the range of the preamp. I am going to try just placing a capacitor in series with the signal and see if that does the trick.

I think I can use a dc-blocking capacitor, but from my readings I believe it is not just as simple as putting a capacitor in series with the signal. It seems that I need a sink for the dc component of the signal, but I am not sure how that all works, particularly because I am using a "black-box"...

Hello all, I am looking for a means of AC-coupling a current input to an amplifier http://www.thinksrs.com/products/SR570.htm . I found some methods to do this with a simple op amp set-up, but I am not sure how to accomplish this with this instrument. The reason I want to remove the DC current...

Yeah, I edited my post after I realized that was incorrect. These are FETs that are made in-house, so there is no part number. It is a MOSFET, and they range from n to ambipolar to p type, so not much help for you there either. They are physically symmetrical, so for experimental purposes the...

I am really grateful for all your responses! This forum is awesome. I didn't fully understand how op amps work, but I am slowly gaining insights as I work through this project. The light source impinging on the phototransistor is actually the interferogram produced by an IR-light source in an...

SMU stands for Source Measure Unit. The basic idea is that it can provide a very responsive constant voltage across a varying resistivity. As a variety of light frequencies impinge on the transistor, the resistivity of the channel will change very quickly. The SMU provides a constant voltage to...

So the way you have VDS set up won't the current just flow from + to - side of the SMU? I don't see why the current would flow through the transistor if it has a direct path from + to -...

Jeff - The idea was to have the current preamplifier and RT in parallel with the SMU. The SMU is very good at fixing a voltage and supplying whatever current necessary to force that voltage. Baluncore - The CPA is made by Stanford Model SR570. It can provide a +- 5V bias, so I may just end up...

Hello all, I am interested in measuring the photoresponse of a transistor with a fixed source-drain bias. I would like to feed the drain current into a current preamplifier and output the preamplifier signal to another location. The preamplifier has a very low current maximum, so I will use a...