+ Post New Thread
Results 1 to 14 of 14
  1. #1
    Member level 5
    Points: 1,305, Level: 8

    Join Date
    Oct 2014
    Posts
    86
    Helped
    0 / 0
    Points
    1,305
    Level
    8

    No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    Hi
    I replaced THS3095 ic on Evaluation Board(http://www.farnell.com/datasheets/20...738.1478693252) with THS3091.
    I am trying to run this op amp from a 24v power Supply such that Vs+ is connected to 24v and Vs- to Gnd. as shown here:Click image for larger version. 

Name:	vs.PNG 
Views:	5 
Size:	23.1 KB 
ID:	147944
    In my circuit, Rf=1k and Rg=110 ohm such that i can get 10 times amplification but it is not amplifying. Also i have removed jp1, jp2, C9 and C10 Capacitors, which were being used in case of THS3095.

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 24,294, Level: 37
    barry's Avatar
    Join Date
    Mar 2005
    Location
    California, USA
    Posts
    4,661
    Helped
    1032 / 1032
    Points
    24,294
    Level
    37

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    When you say "it is not amplifying" does that mean the output is zero? Gain of 1? What does the output look like? What is your input signal?



  3. #3
    Advanced Member level 4
    Points: 8,335, Level: 21
    Achievements:
    7 years registered

    Join Date
    Nov 2009
    Location
    Italy
    Posts
    1,125
    Helped
    386 / 386
    Points
    8,335
    Level
    21

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    Did you properly drive the power-down signal, present only in THS3095 amplifier (pin 8) ?



  4. #4
    Member level 5
    Points: 1,305, Level: 8

    Join Date
    Oct 2014
    Posts
    86
    Helped
    0 / 0
    Points
    1,305
    Level
    8

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    I worked on the schematics and now i am getting 10 times gain as expected. Earlier i was getting only gain of 2. My Input signal is 1Vpp. Also Power Down and REF pins are left NC by removing C9 and C10 and JUMPERS also removed.

    So i did changes in my schematics like this:-
    My Vs is 24V DC.Referring to the above schematics, the Vs/2(12V) voltage which i obtained from a resistor divider(100k) network was connected to the GND terminal of the Evaluation Board and to the +- inputs of the op amp as shown in the schematics above.

    By doing this, i am able to get 10 times Gain. Is it because of Virtual Ground? But still i am getting saturated negative half cycle when my input increases 1.5V Any suggestions to remove this



    •   AltAdvertisement

        
       

  5. #5
    Full Member level 1
    Points: 2,388, Level: 11
    Achievements:
    7 years registered

    Join Date
    Jan 2009
    Posts
    105
    Helped
    16 / 16
    Points
    2,388
    Level
    11

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    With 100k resistor divider, the virtual Ground will get instable. you have 50R termination and 2k5 feedback, pulling/pushing approx. 20mA from this Vgnd.
    So either stabilize this, or use symmetrical supply (+-12V)



  6. #6
    Member level 5
    Points: 1,305, Level: 8

    Join Date
    Oct 2014
    Posts
    86
    Helped
    0 / 0
    Points
    1,305
    Level
    8

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    In the feedback, i have Rf=1k and Rg=110 Ohm instead of 1k2 resistors to get Gain=10



    •   AltAdvertisement

        
       

  7. #7
    Advanced Member level 5
    Points: 24,294, Level: 37
    barry's Avatar
    Join Date
    Mar 2005
    Location
    California, USA
    Posts
    4,661
    Helped
    1032 / 1032
    Points
    24,294
    Level
    37

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    Your Vs/2 should be a low-impedance.



  8. #8
    Super Moderator
    Points: 260,308, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,462
    Helped
    13829 / 13829
    Points
    260,308
    Level
    100

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    Show how you exactly terminated the "Vs/2" node. Also Vi needs capacitive coupling or the source grounded to Vs/2 as well.



  9. #9
    Member level 5
    Points: 1,305, Level: 8

    Join Date
    Oct 2014
    Posts
    86
    Helped
    0 / 0
    Points
    1,305
    Level
    8

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    This is the circuit. There is some mistake here but the output is coming out fine. Problem comes when i increase my Vi from 1V, then the negative cycle goes into saturation so i have to provide around 5mV of offset from Sig Generator to get the ideal output.

    Click image for larger version. 

Name:	GND.PNG 
Views:	8 
Size:	36.2 KB 
ID:	147997



  10. #10
    Super Moderator
    Points: 77,915, Level: 68
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    15,796
    Helped
    3593 / 3593
    Points
    77,915
    Level
    68

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    Hi,

    Iīd like to step back an see the amplifier just as a black box.

    The black box has
    * signal input
    * signal output
    * power supply

    Can you please define:
    * signal input: What is the source? What frequency range (do you need DC coupling?). Is the signal input true floating or is it related (connected somehow) to the power supply or the output outside of the black box?
    * signal output: What is the load? What load impedance? related to which return signal? Is there any additional connection to/from the load to any other device outside the black box?
    * power supply: Is it a true dual supply with 3 (or 4) wires with true (low ohmic) GND at the center tap? What type is it (battery, switch mode, linear...)? whatīs the max current specification?

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



  11. #11
    Member level 5
    Points: 1,305, Level: 8

    Join Date
    Oct 2014
    Posts
    86
    Helped
    0 / 0
    Points
    1,305
    Level
    8

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    My input Signal is from a Sine Wave from Signal Generator with 2V Amp and frequency range is from 50kHz to 1MHz for various setups.
    The load is a piezoelectric Transducer with impedance ranging between 2k and 50 Ohm for various transducers. The output of op amp just goes to the transducer and oscilloscope channels for measuring voltages.
    Power Supply(Traco POWER TPC 120-124) is 24V dc which is also divided down to 12V for using the op amp with a single supply.



  12. #12
    Full Member level 1
    Points: 2,388, Level: 11
    Achievements:
    7 years registered

    Join Date
    Jan 2009
    Posts
    105
    Helped
    16 / 16
    Points
    2,388
    Level
    11

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    Quote Originally Posted by jimmykk View Post
    In the feedback, i have Rf=1k and Rg=110 Ohm instead of 1k2 resistors to get Gain=10
    with these values, Gain is ~11



    •   AltAdvertisement

        
       

  13. #13
    Super Moderator
    Points: 77,915, Level: 68
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    15,796
    Helped
    3593 / 3593
    Points
    77,915
    Level
    68

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    Hi,

    My input Signal is from a Sine Wave from Signal Generator with 2V Amp and frequency range is from 50kHz to 1MHz for various setups.
    The load is a piezoelectric Transducer with impedance ranging between 2k and 50 Ohm for various transducers. The output of op amp just goes to the transducer and oscilloscope channels for measuring voltages.
    Power Supply(Traco POWER TPC 120-124) is 24V dc
    * please confirm that your signal generatorīs output is true floating and not related to earth GND or any other signal.
    * It seems you donīt need DC... then why donīt you use AC coupling with series capacitor as requested?
    * please confirm that your signal generator is able to drive 50 Ohm loads. (Scope)
    * please confirm that your oscilloscope is true floating and not related to earth GND or any other signal.
    * please show both connections of the piezo in your circuit.

    which is also divided down to 12V for using the op amp with a single supply.
    --> then show us this circuit. Why donīt you use this signal instead of the 100k voltage divider?

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



  14. #14
    Super Moderator
    Points: 260,308, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,462
    Helped
    13829 / 13829
    Points
    260,308
    Level
    100

    Re: No amplificaiton observed when THS3091 op amp used on THS3095 Evaluation Board

    A complete schematic would show the source and load ground connections. With the given vague description you need to guess a lot. But it's most likely the 100k + 100k virtual ground divider that makes the circuit fail.



--[[ ]]--