cancel JFET amplifier input capacitance changes

Walt Jung of Analog Devices published an application note about the bootstrap technique used on the negative power rail of AD744 JFET opamp to reduce its input capacitance changes (upon input voltage changes), affecting the amplifier's linearity when connected to high impedance sources.

I would like to know if this technique works with the ADA4817-1 wideband JFET opamp, and which power supply rail should be bootstrapped.

Thanks

Francois

C-VnonlinearityAN232.pdf
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  • Hi Francois,

    In addition, the major difference between ADA4817 and AD744 (the one used in the application note of Walt Jung) is that it uses different polarity of JFET (ADA4817: N-Channel and AD744:P-Channel). It means that the polarity of the Walt's circuit would need to be inverted (drive the opamp's positive supply terminal instead of negative). In principle, this technique would work but I think anyone hasn't tested it.

    Would you mind sharing us your intended application? Thank you.

    Regards,

    Jino

Reply
  • Hi Francois,

    In addition, the major difference between ADA4817 and AD744 (the one used in the application note of Walt Jung) is that it uses different polarity of JFET (ADA4817: N-Channel and AD744:P-Channel). It means that the polarity of the Walt's circuit would need to be inverted (drive the opamp's positive supply terminal instead of negative). In principle, this technique would work but I think anyone hasn't tested it.

    Would you mind sharing us your intended application? Thank you.

    Regards,

    Jino

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