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phase compensation of INA103

Matthias Ikeda
Prodigy 50 points
Other Parts Discussed in Thread: INA103

Hello,

is it possible to compensate the phaseshift of INA103 instrumentation amplifier if the input signal was a 20mVpp sine-function in the frequencyrange from 1Hz to200kHz?

 

In a former thread, i got the advice to use an all-pass filter. but which Op-amp is suitable best for my task??

Thanks in advance for your effort.

 

greets, matthias.

  • 0
    TI__Guru* 93105 points

    Hello Matthias,

    The cumulative phase shift of the stages internal to the INA103 is a normal AC response and is not specified other than stability is implied by the internal compensation. No, it is not possible to add some sort of compensation to the INA103 to eliminate the phase shift from 1Hz to 200kHz. An external filter such as the All-pass filter you mention can provide a means to compensate for the phase shift introduced by the INA103 circuit, but you would need to know how much phase shift that is and understand that won't be a a perfect solution.

    I suggest you download TI's FilterPro V3.1 software and take a look at its all-pass filter synthesis capabilities. The program will provide the operational amplifier minimum gain-bandwidth requirements. Once you have that information you can then decide what else you need in performance from the operational amplifiers. The TI homepage on the web has tools to help you locate and select the best amplifier for the application. You can find TI's FilterPro tool at:

    http://focus.ti.com/docs/toolsw/folders/print/filterpro.html

    Regards, Thomas

    PA-Linear Applications Engineering 

  • 0 in reply to Thomas Kuehl
    Genius 5430 points

    Matthias;

    In addition to what Tom said, I would recommend a good FET or CMOS op amp for your all-pass filter since, on the low end, you need a very low frequency (1Hz) and this implies using high value resistors; low input bias current will be necessary to prevent DC offset errors. Of course if you are using a synchronous detector (lock-in) then DC errors will not be important unless they are so large that they impact your dynamic range. A 200kHz upper end will require an op amp with a gain-bandwidth of about 10x that frequency or higher.

    There are plenty of op amps that fit this requirement, so you might select your device on the output voltage swing and power supplies that you have available.