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

voltage drop across a current source

Status
Not open for further replies.
A

antaryami.mt.er09

Member level 2
Joined
Aug 14, 2010
Messages
49
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,288
Location
INDIA
Activity points
1,576
Hi...
can anyone tell me how can calculate the voltage drop across a current source in presence of another components?
 

A current source has its voltage defined by its load. V=IZ.
A voltage source has its current defined by its load. I=V/Z.
 

checkmate said:
A current source has its voltage defined by its load. V=IZ.
A voltage source has its current defined by its load. I=V/Z.
Click to expand...

say i have diffirential amplifier and a tail current source of 10mA and vdd=5 v.How can i calculate the voltage drop .After simulation it shows Vsat=some voltage .
 

Could you please post the schematic diagram ?
 


i am attaching the image .

---------- Post added at 11:19 ---------- Previous post was at 11:16 ----------
albbg said:
Could you please post the schematic diagram ?
Click to expand...

in the diagram i 've shown the mos as a current source .If i replace it with a current source I1 then how can i calculate the voltage drop across it
 

The circuit is a series of Isource and Z, where Z is the impedance due to RL and the MOS. In general, if Vi is the voltage across the Isource, will be:
(Vdd-Vss) = Vi + Z*Iss

If two MOS are driven alternatively into conduction, Z will be approx equal to RL so Vi = (Vdd-Vss) - RL*Iss

If, instead, they can, under some circustancies, go from both open to both closed passing through the linear region:

Both open: Vi = 0 since Z tent to infinite - This is the minimum possible current
Both closed Vi = (Vdd-Vss) -RL*Iss/2 since the twor RL are in parallel - This is the maximum possible current
Linear zone, depend from the impedance of each MOS channel
 
You consider the case where Vin is shorted to some input voltage.
If Vin<Vdd-0.5*Itail*RL+Vth, input stage is operating in saturation, and the tail voltage is simply Vin-Vgs.
Else, the tail voltage is Vdd-0.5*Itail(RL+Rdson).

As I mentioned before, the potential difference of a current source depends solely on its load, which in this case are MOSFETs (and resistors), whose operating mode is dependent on Vin, the biasing current and MOSFET dimensions.
 
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top