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OFFSET TRIMMING INA333

MSP430-Beginner
Intellectual 660 points

Other Parts Discussed in Thread: INA333

In the data sheet of INA333, there is a paragraph talking about offset trimming of INA333. I don't really understand the usability of the offset trimming. Is it about the offset at the output, when the diff input voltage is at 0V? So why do we need Vref? Is there a certain Vref, at which when the diff input voltage is 0V, the output is also 0v?

Thx!

  • 0
    Guru 21975 points

    Sometimes a +/- input signal voltage is converted to a digital value with a unipolar A/D converter. A half-scale voltage is applied to the Ref terminal of the instrumentation amplifier so that a 0V differential input voltage is shifted to half-scale of the A/D converter. This allows bipolar signal processing.

    Regards, Bruce

  • 0 in reply to Bruce Trump
    Prodigy 105 points

    Hi,

    I've been using the INA333 to make an EMG amplifier. I connected a second order low pass MFB butterworth filter at @20Hz cutoff , which filters the INA333 output and feeds it to the reference pin. I am not pleased with the results. while the DC correction seems to work well, at lower frequencies the signal is not attenuated much, and instead is kind of a square wave output even at low amplitude input. 

    I was wondering, does the ref pin operate with a varying signal? say, if i input a DC shifted sine wave at the Vref, will the output contain the same signal added to it?