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# Convert voltage to current linearly without using opamp?

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#### shanmei

Any idea how to convert voltage to current linearly without using opamp or just using simple circuit?

For example, Vin=1V, the output current will be 100uA.
Vin=2V, the output current will be 200uA.

Do not use power-consumption circuit, such as opamp. Thanks.

If accuracy or stability is not a huge consideration then just connect a resistor in series. Looking at your values 10k resistance will work.

If accuracy or stability is not a huge consideration then just connect a resistor in series. Looking at your values 10k resistance will work.

Thanks.

Sorry, I forgot to mention that the voltage has no driving ability, so it can not driver the resistor.

Just like the voltage is from a small capacitor( 1pF )

Shanmei;

you can't arbitrarily have conflicting requirements, and expect valid solutions.

If the voltage source is equivalent a 1 pF capacitor, you will not only have to have an opamp to perform the V/I conversion, but the opamp itself must be a precision instrumentation amplifier with ultra low Ib. Additionally, to prevent surface leakage, the input must surrounded by a guardband driven by a second opamp.

cyrax747

### cyrax747

Points: 2
Anything you connect will have a much larger capacitance than 1pF.

And how would you expect to do this without a power consumption circuit? You have to have power to amplify a signal.

1pF is the capacitance between two poles on both sides of a road, almost nutthin'. There will be no current and you will not be able to measure its voltage. Why bother thinking about it?

1 pF charged at 1 volt, will be fully discharged in 10 nanoseconds by a current of 100 microamps.

Yes, it is a prepostperous request.

A FET (JFET or MOSFET) in common source configuration with internal feedback can act as a voltage to current converter without needing additional quiescent current. Of course it's less linear than an OP circuit.

shanmei

Points: 2