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AD8139 Not Working. I need help

I am using the AD8139 in the as shown in the attached PDF.

Spice simulations work fine. But On the bench using +-5V supplys,  AD8138 outputs Nothing.

What did I do wrong.

Stan Schekall a783239d66076ba983835f6e0157fe05.pdf

osc_5MHZ.pdf
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  • Hi Stan,

    Let me step back and ask a question, why you have selected this topology for the AD8139? While it is unique, this topology does have some disadvantages, such as being noisier that a traditional 4 resistor topology. It is not a circuit we commonly recommend or publicize; as it does not provide the best performance that can be attained by our amplifiers and can have issues as we are seeing. Going through the design equations, you’ll see the Vocm noise does not get cancelled out and more noise from other sources is present using this configuration. I’ve attached a slide here, that you can use to calculate and compare the two circuits. My recommendation would be to convert the circuit to a 4 resistor topology.

    cid:image001.png@01CBD9BC.548F5630

    I hope this helps

    Regards

    Jack

    From: sschekall analog@sgaur.hosted.jivesoftware.com

    Sent: Thursday, March 03, 2011 12:42 PM

    To: Ardizzoni, John

    Subject: New message: "AD8139 Not Working. I need help"

    Analog Devices EngineerZone<http://ez.analog.com/index.jspa>

    AD8139 Not Working. I need help

    reply from sschekall<http://ez.analog.com/people/sschekall> in Differential Amplifiers - View the full discussion<http://ez.analog.com/message/20319#20319

Reply
  • Hi Stan,

    Let me step back and ask a question, why you have selected this topology for the AD8139? While it is unique, this topology does have some disadvantages, such as being noisier that a traditional 4 resistor topology. It is not a circuit we commonly recommend or publicize; as it does not provide the best performance that can be attained by our amplifiers and can have issues as we are seeing. Going through the design equations, you’ll see the Vocm noise does not get cancelled out and more noise from other sources is present using this configuration. I’ve attached a slide here, that you can use to calculate and compare the two circuits. My recommendation would be to convert the circuit to a 4 resistor topology.

    cid:image001.png@01CBD9BC.548F5630

    I hope this helps

    Regards

    Jack

    From: sschekall analog@sgaur.hosted.jivesoftware.com

    Sent: Thursday, March 03, 2011 12:42 PM

    To: Ardizzoni, John

    Subject: New message: "AD8139 Not Working. I need help"

    Analog Devices EngineerZone<http://ez.analog.com/index.jspa>

    AD8139 Not Working. I need help

    reply from sschekall<http://ez.analog.com/people/sschekall> in Differential Amplifiers - View the full discussion<http://ez.analog.com/message/20319#20319

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