Differential amplifier design

Thread Starter

Alexx98

Joined Nov 5, 2017
30
I have a problem about giving values to resistors to have high differential gain. Also I am not sure I set up the circuit correctly on Ltspice.
 

Attachments

ebp

Joined Feb 8, 2018
2,332
Your PNPs are in the circuit backwards and there are missing connections on the lines labeled as outputs.
 

Thread Starter

Alexx98

Joined Nov 5, 2017
30
Your PNPs are in the circuit backwards and there are missing connections on the lines labeled as outputs.
Thank you! I changed the output part but the only pnp model that I find is this one. The desired pnp model is 2N2907, I can't fix this. I'm not familiar with Spice
 

Attachments

ebp

Joined Feb 8, 2018
2,332
You simply need to flip the symbol top-to-bottom. I don't know how you do this in LTspice since I don't use it, but there are probably mirror and rotate operations e.g. rotate 90 degrees twice then mirror

edit: there may be a mirror vertically operation which does what is required in one step
 

Thread Starter

Alexx98

Joined Nov 5, 2017
30
You simply need to flip the symbol top-to-bottom. I don't know how you do this in LTspice since I don't use it, but there are probably mirror and rotate operations e.g. rotate 90 degrees twice then mirror

edit: there may be a mirror vertically operation which does what is required in one step
Yes, thank you now it is all done I think :)
 

Attachments

ebp

Joined Feb 8, 2018
2,332
You should/must (?) name the two outputs differently. If they have the same name the simulator may consider them to be connected.

.tran 4mS (assuming that is correct syntax, which again I don't know) should be
.tran 4ms - lower case s for seconds, upper case for Siemens (unit of transconductance)
 

Thread Starter

Alexx98

Joined Nov 5, 2017
30
You should/must (?) name the two outputs differently. If they have the same name the simulator may consider them to be connected.

.tran 4mS (assuming that is correct syntax, which again I don't know) should be
.tran 4ms - lower case s for seconds, upper case for Siemens (unit of transconductance)
The given circuit names them as the same Vout. But I'm changing it in LTspice now. Thank you again.
 

crutschow

Joined Mar 14, 2008
23,291
The given circuit names them as the same Vout.
The original circuit names the differential output from the two outputs as Vout.
Spice connects all nodes with the same name together, so you need to label the two inputs and two outputs with different names.
I've sometimes been puzzled by strange simulated circuit behavior when I've inadvertently given two different nodes the same name and Spice dutifully connects them together. :rolleyes:
 
Top