BJT differential amplifer

D

derek

Guest
Hi,

If I have a differential input voltage and want to output a current to
be proportional to it, how to create a circuit using BJTs to do that?
Thanks!
 
derek wrote:

Hi,

If I have a differential input voltage and want to output a current to
be proportional to it, how to create a circuit using BJTs to do that?
Thanks!

You're describing the input stage to an opamp. Search around until you
find a data sheet for something simple like a 741 or an LM353 and look
at the input stage.

If you want to do it in real life you need matched transistors, though.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
derek wrote:
Hi,

If I have a differential input voltage and want to output a current to
be proportional to it, how to create a circuit using BJTs to do that?
Thanks!
You have severely under specified the problem. What range of
differential voltage must the circuit respond to? What output current
per volt of input do you require? What voltage range must the current
source comply with? What load resistance can the differential
amplifier apply to the input voltage? What frequency range is
involved? Etc.

You are not ready to even start thinking about circuit designs till
you have the problem nailed down.

--
John Popelish
 
"derek" <dereklai2k@yahoo.com.hk> ha scritto nel messaggio
news:1103950095.546699.5680@c13g2000cwb.googlegroups.com...
Hi,

If I have a differential input voltage and want to output a current to
be proportional to it, how to create a circuit using BJTs to do that?
Thanks!

you need a differntial Gm cell....
it's possible to create a programmable Gm cell where Iout= Gm_code*Vin_diff
it's very important f you want to realize it using discrete component to use
a feedback to cancel the mismatch of the compnent...reed Pelgrom's paper on
this topic
anyway you should give some spec on your circuit...
 

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