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Design >> Analog Design >> Voltage Controled Current Source
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Message started by XY-oriented on Apr 29^th, 2009, 6:58am

Title: Voltage Controled Current Source
Post by XY-oriented on Apr 29^th, 2009, 6:58am

hi all,
does any one has a circuit idea of how to realize a voltage controlled current source?
the obvious solution is to use a resistor and an op amp in feedback but then I have 20% variation (actually more with the process I am using) witch is very high.

in principle I can give up linearity for a more process independent current source ...

maybe some simple self calibration ideas ?

any comment would be helpful :'(

thanks

Title: Re: Voltage Controled Current Source
Post by raja.cedt on Apr 29^th, 2009, 8:12am

hi XY-oriented,
i think if use source degenerated mosfet with good loop gain(gm*r),it wont change much process i am sure i will be lees than an op amp.try this different corners

Thanks,
Rajasekahr.

Title: Re: Voltage Controled Current Source
Post by ndnger on May 9^th, 2009, 9:53pm

Can you use a differential pair with a BG referenced tail current source. Now, connect the drain(collector) of one side to supply and use the output from the drain(collector) of the other side as your VCCS.

You will have to bias one side of the differential pair to a constant (BG referenced voltage like a BG current flowing through a resistor). The other side of the diff pair will be controlled by Vctrl.

In order to lower the output current Vs vctrl slope, use degeneration resistors. The knee voltage of the current source will be Vctrl minus one overdrive voltage for MOSFETs. So, you should minimize the fixed bias voltage applied to the left side of the diff pair (/w o/p taken from right side).

cheers!

Title: Re: Voltage Controled Current Source
Post by XY-oriented on May 10^th, 2009, 9:34am

Rajasekahr and ndnger , Thank you for your comment and suggestions.

ndager idea seems to give nice simulation results ...

cheers!