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

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jimmykk

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Hi
I replaced THS3095 ic on Evaluation Board(**broken link removed**) 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: vs.PNG
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.
 

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?
 

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

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
 

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)
 

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

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

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.

GND.PNG
 

Hi,

I´d 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...)? what´s the max current specification?

Klaus
 

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.
 

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 generator´s output is true floating and not related to earth GND or any other signal.
* It seems you don´t need DC... then why don´t 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 don´t you use this signal instead of the 100k voltage divider?

Klaus
 

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.
 

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