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

Why use of current source as load?

Status
Not open for further replies.
S

shemo

Advanced Member level 4
Joined
Apr 26, 2002
Messages
105
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,296
Activity points
709
1)Current source is used as load because gmRout=gain. increasing the Rout(impedance) will increase the gain.
But the impedance of current source is parallel the first stage output impedance and the output impedance of the first stage << impedance of the current source therefore the final impedance is just output impedance of the fist stage.

the load stage impedance current source is take out.

So,, the question, is why use the current source as load?
 

shemo said:
... why use the current source as load?
Click to expand...

A resistive or a (transistor connected as) diode's output impedance might be < or << than the output impedance of the first stage.

Or perhaps a bias voltage for the current load is available anyway - so why not?
 
Last edited:

The best you can do for gm*Rout is the self-impedance of
the gain stage. Using "as ideal as possible" a load (current
source) at least doesn't make things worse. Try a resistor
sometime.

Although some regenerative loads (e.g. cross-coupled) can
perhaps improve the net gain beyond an ideal current source,
if done right (I've found them not worth the trouble mostly).
 

I think the output impedance of a common emitter transistor is very high because it is a current source or sink, it is not a low impedance voltage source. Then when its load is a high impedance current source or sink its voltage gain is very high.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top