[Moved]: linear voltage to current converter

[shanmei]

Do you know how to build a low power linear voltage to current converter? The voltage to current conversion needs to to very high precision, like 10bit resolution.

This opamp based V/I is good, but the opamp will consume large power consumption. Since I need a fast response Voltage to Current, the opamp needs to be large bandwidth to follow the input voltage change.

The other schematic is good, but the linearity is not so good as the opamp based one.

Do you have any other idea to build a low power fast voltage to current converter ? Thanks.

 

[erikl]

Re: linear voltage to current converter

Do you have any other idea to build a low power fast voltage to current converter ? Thanks.

Depends on the output impedance of your voltage source (should be low) and the input impedance of the circuitry which receives the converted current (should be low, too). Say these output and input impedances are 100Ω, a simple resistor of ≧ 100kΩ should do the conversion with a 10-bit (in-)accuracy.

 

[FvM]

Re: linear voltage to current converter

Sorting out trivial cases like the simple resistor converter, I don't believe that you'll achieve 10 bit accuracy without a feedback amplifier.

 

[D.A.(Tony)Stewart]

Re: linear voltage to current converter

10 bit accuracy implies R tolerances must be less than the 0.1%.

 

[shanmei]

Re: linear voltage to current converter

Depends on the output impedance of your voltage source (should be low) and the input impedance of the circuitry which receives the converted current (should be low, too). Say these output and input impedances are 100Ω, a simple resistor of ≧ 100kΩ should do the conversion with a 10-bit (in-)accuracy.

Thanks.

Actually, both the input and output impedance is large. That's the problem.

 

[shanmei]

Re: linear voltage to current converter

Sorting out trivial cases like the simple resistor converter, I don't believe that you'll achieve 10 bit accuracy without a feedback amplifier.

Can you please draw the schematic to realize it with opamp? Thanks.

 

[D.A.(Tony)Stewart]

Re: linear voltage to current converter

Can you please draw the schematic to realize it with opamp? Thanks.

Can you please specify your exact output impedance, signal qualities( range, frequency , rise time) and available power stability, operating temperature range, plus list any potential sources of EMI.? etc.

Any design must have all constraints given.

 

[electronics_rama]

Hello shanmei,

I suggest you to go for a structure where your input MOS will operate in linear region and with a cascode MOS on top of it. The cascode MOS should be driven with a opamp in feedback. This will surely give you a higher linearity.