Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

lograthmic opamp circuit not working

Status
Not open for further replies.

aliraza786

Full Member level 4
Joined
Nov 10, 2009
Messages
210
Helped
14
Reputation
28
Reaction score
14
Trophy points
1,298
Location
Lahore, Pakistan, Pakistan
Activity points
2,914
i wana make a circuit which can able to take log of any voltage applied at non inverting input i attached a circuit in the form of pic...and i also dnt know which bising resisatcne should i use for transistor to work prpoerly....

 

Try this circuit:
your input can be variable from some mv to some volts( for example 50v) ( i think)
untitled.JPG
 

I don't think, that the circuit from the original post is not working. It has a temperature dependent offset voltage by design, which is common to all one-transistor (or one-diode) circuits. For better results, you need to refer to a compensated dual-transistor circuit from text books.
 

sir FVM
please tell me more about compensated dual-transistor circuit........and goldsmith in ur circuit 1mv is as input and ln(1mv) is -6.90 but in your case it is 448 mv........and what is the effect of temperatire on the output of the circuit.......?? and also in simulation temperature does effect the output or not or this is a real time application eror.......??
 

The dual transistor circuit is shown in the literature posted by Goldsmith on page 9.

The output of the simple one-transistor circuit is -26 mV * ln(I1/Is), with Is being a transistor parameter. The 26 mV slope is valid for 25°C and proportional to absolute temperature T = t +273°. You'll find more calculation details in the literature.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top