For higher accuracy data acquisition capability, it is a challenge for the test and measurement equipment designer to measure small signal variations when high common mode voltages (wanted or unwanted) are interfering with the system. These high voltages exist due to the different potential in the two grounds or any sudden transient over voltages due to lightning strikes or power surges from motors or switching devices. These voltages do not only impact on the accuracy of the measurement, but also damages the test systems and cause hazards to people operating the tester.