[SOLVED] how to remove +1.4 v offset from instrument amplifier output using op amp

[ud23]

hi i want to remove 1.4v offset voltage from the amplifier output. and i want its ckt can i use differential amplifier?

 

[FvM]

You can also feed an offset voltage to the reference input. But it should be low impedance, e.g. buffered by an OP voltage follower.

 

[alexan_e]

sure you can



You can ground VR and apply a +1.4v in the V1 input, you can set the gain to 1 if no gain is needed.
Your signal will be connected to V2.

An alternative would be to ground V1 and apply a negative voltage (-1.4v) to VR

Alex

 

[ud23]

hi thnax for help but i don't get difference output i used R1=1kohm,Rf=4.2k and set 1.4v at v1 but getting output same with offset of 1.38v i don't need gain so can i use Rf=0ohm?

 

[alexan_e]

If you check the equation you will see that you have to use the same value for all resistors to have a gain of 1.

R1=1kohm,Rf=4.2k gives a gain of 4.2 , the gain is Rf/R1

Aex

 

[ud23]

ya thanx and i am using op amp with single supply so do i need use refinance voltage at non inverting input.??

 

[alexan_e]

Yes you should use +1.4v to the inverting input and Vr to gnd

Alex

 

[ud23]

ya its working now i changed all resistor to same value so i am getting difference voltage now.

 

[FvM]

You didn't tell about the used instrumentation amplifier or the circuit, but what's the reason for output offset? If the instr-amp is operated from single supply, it may be trivial output saturation. Then shifting the output won't help much.

 

[ud23]

ya Fvm i am using instrumentation Ic Ina125 and i am using it with single supply so dose this circuit work?

 

[FvM]

Datasheet figures 5 and 6 are discussing different kinds of single supply operation. I don't know which is better meeting your application. If you need a bipolar output signal, then IAref need to be connected to a positive "pseudoground" or virtual ground as in figure 6. The output will have an offset, but you can hardly remove it without losing the bipolar signal swing. If your signal is unipolar, but the signal has an unwanted offset, which would be originated from the input, an additional differential amplifier, as suggested by Alex, can help. But you should consider, that no single supply amplifier can achieve exactly zero output.

Another imnportant point with instrumentation amplifiers is keeping the input common mode range. Related to single supply operation of INA125 this implies a positive bias voltage to be applied to the inputs.

 

[ud23]

Sorry for late a update, i am having problem to take output signal for offset removing circuit as input signal.Basically i am using INA125 with single supply and if i check output from pin no. 11 with reference with pin no.5 i am having offset voltage of +1.4v if i check output from pinno.11 and with reference ground its show output as 3.57v(whether offset i don't know)so how i can take signal for my offset removing circuit?????

 

[flak1]

hi I have the same problem with the ina125 I don´t know how to remove the offset, in the out I have 0.05 V when at the entry I have 0 V, I don´t know how I cn use the vref pin please help me I´m using the amplifier eith a single supply
thanks for your help