Stable Ac current source

Discussion in 'The Projects Forum' started by sanoua20, Dec 6, 2011.

  1. sanoua20

    Thread Starter New Member

    Dec 6, 2011
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    hey everyone
    i really really need your help , so please don't hesitate on answering or posting anything that make sens to you.

    I am not an expert in analogical electronics and am supposed to build a AC current source that is very stable and can deliver an current with Imax=0.355µA
    the frequency is about 0 - 20KHz

    am really desperate
    i will be gratefull for any help and thank u in advance
     
  2. jimkeith

    Active Member

    Oct 26, 2011
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    What is the voltage limit of said current source? e.g. 10V, 24V, etc.
    Also, how stable?
    I assume that it is also variable in that the Imax is stated.
     
  3. sanoua20

    Thread Starter New Member

    Dec 6, 2011
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    the voltage limit is 15 V
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
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    This is an extremely low level, apparently specified to a precision of nano-amps.

    How perfectly constant-current does it need to be? It occurs to me that you might get away with a voltage source of some tens of volts followed by a large resistance.
     
  5. sanoua20

    Thread Starter New Member

    Dec 6, 2011
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    well this source will feed a sensor so it has to be very stable
     
  6. jimkeith

    Active Member

    Oct 26, 2011
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  7. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Numbers are needed here - "very stable" is too vague. What are the upper and lower limits for the drive level? Do you know what the sensor impedance is, and if relevant how it varies over the frequency range?
     
  8. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Depending on the sensor impedance, careful guarding of cable runs or even PCB tracks to the device may be required to get 20kHz bandwidth with nA precision.
     
  9. sanoua20

    Thread Starter New Member

    Dec 6, 2011
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    0
    ok ,
    i really don't have much of informations all i know is that the current will feed a capacitive sensor , and that the current source will be connected to a quartz oscillator
    i also have this equation
    v=I/(jwc)=I*d/(jwES)

    f = 32 kHz (oscillator frequency), V = 0 to 10 V. So if we take V = 10 V and d=0.2 mm, S= 4 mm² you can calculate the rms value of I to be constant. E = 8.854 10^12F/m the primitive of the space

    hope i made a little bet clearer
     
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