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THS4082: Buffer Amplifier Application - Unexpected attenuation between 10 and 30 MHz

Part Number: THS4082

We use the THS4082 OP-AMP as a buffer amplifier in an oscilloscope application as input buffer to achieve a high input impedance. The OP-AMP is supplied with +-11 V and the signal range we are aiming for is approx. +-5V. The oscilloscope shall have a bandwidth of 50MHz and so we chose this OP-AMP with a small signal bandwidth of typ. 170MHz. However we see an attenuation in the range of 10 - 30 MHz which we can't explain. At 40MHz the gain increases again and at 50 MHz is at 1 as expected. Values above we could not test because of the limited bandwidth of our signal generator.

Our test setup contains only of the supplied OP-AMP as buffer amplifier and the input and output signals attached to the signal generator and a reference oscilloscope. For various frequencies we input a sinusoidal signal with a Vpp of about 1V and measured the output signal.

Has anyone else experienced this behaviour, or an idea what could cause this attenuation in a limited band?

Are there any reference designs for this OP-AMP as a buffer amplifier?

Best Regards

Christian

  • Hi,

    The THS4082 bandwidth does start to roll off around 30 MHz depending on the supply and feedback resistor. It then peaks back up from the second pole effect in the response of the amplifier. You can see the effect over various conditions in the datasheet starting at figure 15. If you are looking for a perfectly flat large signal bandwidth up to 50 MHz, it would be best to choose a faster device.

    Regards,