Hi, I try to measure a AC signal across a resistor at 1MHz using reference design CN0385, where the difference signals (with relatively a large common mode voltage) are converted to single-ended using AD8251. I build this schematic using LTSpice.
However, I found that,
1. The voltage at the Vp node might be affected by the installation of AD8251. With AD8251 removed, V(vp) is a normal ac voltage signal with Vpp = 1.6V. However, when AD8251 is connected, V(vp) becomes,
which is centered above 0V and is around 2V. Although, V(vp) - V(vn) is the same regardless of AD8251.
2. The output of AD8251 is always tied to -5V.
3. I found that the slew rate of AD8251 is only 20V/us, can AD8251 still be used in my applications where the frequency of ac signal is 1MHz, and the Vamp is around 3V to 7V ? It not, is there alternative ICs that can be used in this application ? (note that there is a large, high frequency common mode voltage when measuring ac signal across a resistor out of many resistors)
Thanks all in advance!
Based on the value of the excitation current and series resistance of R_mn and Rn that you mentioned, I computed the needed slew rate of the inamp and it is around 20V/us. This is already the…