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.

Register Log in

Difference between two circuit.

Status
Not open for further replies.
L

ljy4468

Full Member level 4
Joined
Jul 20, 2005
Messages
232
Helped
13
Reputation
26
Reaction score
1
Trophy points
1,298
Location
South Korea
Activity points
3,023
Hi, all

I'm confused with below two BJT circuit.

These are simple comparator, and of cource upper circuit has higher gain.

But I cannot understand intuitively in case of BJT.

Does anyone clarify this?

thanks.
 

Both circuits don't make much sense. The first one seems to be an erroneous attempt to build a differential current mirror, the second is just another artefact, designed by omitting two transistors from the first. Both circuits have no gain at all.
 

In the upper circuit, the cross coupled devices add positive feedback to the circuit, thus increasing the gain. If the voltage at the base of the top right PNP current mirror drops, more current from the left branch will be 'stolen' from the diode on the top left, increasing the imbalance further, etc..

The bottom circuit is just a low-gain differential amplifier..
 

Yes, you're right, I didn't realize the positive feedback. The output swing is limited to about 0.5 V, however.
 

The first circuit is common mode amplifier circuit, Second one is differential amplifier
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top