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
