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
  • 0
    •  Analog Employees 
    on Feb 24, 2011 7:38 PM

    Hi Stan,

    Interesting question, the circuit as shown should work and your simulation says so too. It sounds like something basic, have you traced out your circuit, to see where the signal stops? Is the supply current correct? Is the feedback taken from the right output? What is your input signal amplitude? Just for clarification purposes, this circuit actually has a gain of two and not one. Let me know how it goes and what else I can do to help, you can send me a personal message if you want to take this offline and get more into the circuit details.

    Regards

    Jack

  • John A

    I belive the design is correct. Because replaceing AD8139 with AD8138 works.

    (I also many different AD8139 parts to insure I not debugging a dead chip)

    I switched to AD8139 because I needed higher Temprature performance.

    Also spice simulation and Bench tests( With AD8138)  shows GAIN=1.

    I'm very confused.

         Stan

  • 0
    •  Analog Employees 
    on Mar 4, 2011 2:59 AM

    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

  • John

     

    It's a Legacy design.

     

    Earlier Versions of the design used AD8138, Same configuration, and

    worked much better that expected.  Except for Temp > 100C

     

    Current design is an attempt to work at much higher Temp. Simply replace

    AD8138 with AD8139 no problem.

     

    But AD8139 does not work. I was trying to avoid a costly re-design.

     

     

    Stan

  • 0
    •  Analog Employees 
    on Mar 5, 2011 1:07 AM

    Hi Stan,

    Would you perform a test for me? On the working AD8138 please take a set of node votlages and note the supply current and then do the same for the AD8139. Also what is the Amplifude of Vmax and Vac?

    Regards

    Jack