Op-amp question - Electronic Circuits Projects Diagrams Free

col_implant · 27th November 2007, 11:09 PM

Maybe this is a silly question....

Is it possible to apply a level shift to a transimpeedance amplifier? I searched google and only got patents as results... this tells me no!

jeg223 · 28th November 2007, 12:21 AM

you can pull the input signal up to whatever level you want. It works like a linear combination circuit. If you use a voltage source make sure the input resistor is equal to the feedback resistor so your offset gain is unity.

col_implant · 28th November 2007, 12:55 AM

I was thinking of using a PIC Comparator reference voltage, output directly to V+ input.

The currents I'm measuring are quite small (100pA min). Could noise on the reference be a problem? Perhapps decoupling required?

jeg223 · 28th November 2007, 01:25 AM

Don't you have to worry about the input bias currents at that point?

col_implant · 28th November 2007, 01:37 AM

Wel input bias is of the order of 1pA, quite a good amp we are using

jeg223 · 28th November 2007, 02:12 AM

In that case, Vout= V+ - Rf* Iin
Although bias current and offset voltage may make life miserable.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Title	Starter	Forum	Replies	Latest
Capacitor Charge/Discharge question	ThermalRunaway	General Electronics Chat	25	12th August 2008 05:48 PM
Clamp output of op amp	dazza000	Electronic Projects Design/Ideas/Reviews	21	9th November 2007 09:32 AM
Basic Transmission question	CamNuge	General Electronics Chat	2	8th March 2006 11:08 PM
Data Logging question with high speed!!!!	cubdh23	General Electronics Chat	4	16th August 2004 07:33 PM
PBX question	waqar	Electronic Projects Design/Ideas/Reviews	0	30th March 2003 07:21 PM

27th November 2007, 11:09 PM	(permalink)
col_implant	Op-amp question Maybe this is a silly question.... Is it possible to apply a level shift to a transimpeedance amplifier? I searched google and only got patents as results... this tells me no!

28th November 2007, 12:21 AM	(permalink)
jeg223	you can pull the input signal up to whatever level you want. It works like a linear combination circuit. If you use a voltage source make sure the input resistor is equal to the feedback resistor so your offset gain is unity.

28th November 2007, 12:55 AM	(permalink)
col_implant	I was thinking of using a PIC Comparator reference voltage, output directly to V+ input. The currents I'm measuring are quite small (100pA min). Could noise on the reference be a problem? Perhapps decoupling required?

28th November 2007, 01:25 AM	(permalink)
jeg223	Don't you have to worry about the input bias currents at that point?

28th November 2007, 01:37 AM	(permalink)
col_implant	Wel input bias is of the order of 1pA, quite a good amp we are using

28th November 2007, 02:12 AM	(permalink)
jeg223	In that case, Vout= V+ - Rf* Iin Although bias current and offset voltage may make life miserable. Last edited by jeg223; 28th November 2007 at 02:17 AM.