What‘s wrong with my THS4631

[heroxue]

Yesterday,I used the THS4631（FET-INPUT Amplifier from TI） as inverting amplifier,but I can't get a right wave,but OPA690 could work well in my pcb board.Even I connected Non-Inverting input pin with GND,I can still get a wave as shown below.Then I Built it into the voltage follower was also not correct.So,Please tell me what's going wrong,Thanks!

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My PCB board
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Connected Non-Inverting input pin with GND,Output wave
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Input 13.23KHz,Output wave​

 

[keith1200rs]

I think a circuit diagram would be a lot more useful than the photographs if you want some help!

Keith.

---------- Post added at 13:10 ---------- Previous post was at 13:08 ----------

A wild guess is that you don't have enough supply voltage for the THS4631 or are not operating in its common mode voltage range.

Keith

 

[heroxue]

My circuit is as shown below,just work as inverting amplifier.
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[keith1200rs]

THS4631 should work provided your input is centred around 0V. It is not a great choice for +/-5V operation because the input/output voltage range gets nowhere near the voltage rails. The OPA690 is better in that regard.

Keith.

 

[heroxue]

Thanks Keith for your friendship.
I have instead the THS4631 with another one,and change the powersupply to +/- 10V,but the same situation,just the frequency of output wave(connected Non-Inverting input pin with GND) become lower.I used THS4631 becase it's FET AMP,and I need a high input impedance amp in my analong front circuit.
Are there any questions?
Thanks!

 

[keith1200rs]

I don't see any decoupling capacitors next to the chip, although you have drawn them. The THS4631 is pretty fast and it is possible it is oscillating but you won;t be able to see it on your oscilloscope. Add some decouplers right next to the chip, including something around 100pF.

Also, it looks like it will be pretty unstable without some capacitance across the feedback resistor. Try adding add least 10pF across the feedback resistor.

Do a DC sweep and see what happens - slowly change the input voltage and see if it does anything useful somewhere in its supply range.

Keith.

 

[heroxue]

I have added 6.8pF and 12pF across the feedback resistor,But as if nothing helped.
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the bottom of the pcb borad​

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6.8pF and 12pF across the feedback resistor,Output wave​

 

[keith1200rs]

I think you need to do a DC sweep and look at the voltage on all the opamp pins. Also, add 100pF across the decouplers - the values you have used will not be effective at the frequencies the opamp can work at.

Keith.