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[50 pts] Current source design

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AdvaRes

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current source design

Hi members,

I'm planning to design a constant current source for a charge pump. Could you please help by refering me to the appropriate document to read ?
What are the issue to take in consideration for a designing a good constant current source with deep submicron technology.

Thanks in advance.
 

Monady

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are you sure that charge pump circuit works with constant current source? as i know you can use of 4 MOS transistors and one capacitor for charge pump circuit.
 

    AdvaRes

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rfsystem

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To understand your design intention I will restate:

You want to built a charge pump for DC-DC voltage upconversion which operate in current source mode which is controlled purely on the low voltage side?

Is that right?
 

    AdvaRes

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diemilio

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By constant you mean across process variations? temperature? supply ripple/drift? all of the above?

I'm asking cause sometimes you need the output of your charge pump to be a function of one of these parameters and not necessarily independent of them. Also, depending on your needs, the design may be different.

diemilio
 

    AdvaRes

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AdvaRes

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I'm aware only on temperature (-25 to 85°C).
 

diemilio

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Designing a temperature independent current reference is quite complicated cause, in general, for references you always use voltages as your temperature measuring mechanism (Vth, Vbe, ΔVbe) so then, you would need a resistor you generate the current (making the current's tempco proportional to the resistors tempco). So what is usually done is either use low tempco resistors (which might not be available in your process so it would have to be external) or design a VOLTAGE reference, and then use a Gm (Transconductance) circuit to get the current.

Check out the following paper, it should have what you're looking for...

"A New Low Voltage Precision CMOS Current Reference With No External Components"; Rasoul Dehghani and S. M. Atarodi; IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—II: ANALOG AND DIGITAL SIGNAL PROCESSING, VOL. 50, NO. 12, DECEMBER 2003

Hope this helps,

diemilio
 

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AdvaRes

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Yeah !
That's a good reference. Thanks diemilio.
Thanks for all.

Cheers,
Advares.
 

buckaroo

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Re: current source design

AdvaRes said:
Hi members,

I'm planning to design a constant current source for a charge pump. Could you please help by refering me to the appropriate document to read ?
What are the issue to take in consideration for a designing a good constant current source with deep submicron technology.

Thanks in advance.
The larger output impedance, tha better;
The larger Vdsat, the better pnoise, while the smaller headroom.
 

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