What is the impact of common mode noise on differential signal measurements and how can it be minimized?

The impact of common mode noise on differential signal measurements is that it can reduce the accuracy and reliability of the measurements if not properly addressed. Common mode noise is unwanted electrical noise that appears equally on both conductors of a differential signal pair, relative to a common reference point (e.g., ground). Differential signal measurements are designed to reject common mode noise. A differential amplifier measures the difference in voltage between the two conductors of the signal pair, effectively canceling out any signal that is common to both. However, if the common mode noise is too large or if the differential amplifier is not perfectly balanced, some of the noise can be converted into a differential signal, which will then be amplified and appear as noise in the measurement. For example, in a 4-20mA current loop used to transmit sensor data, common mode noise can be induced by nearby electrical equipment or by ground loops. If the common mode noise is strong enough, it can cause the measured current to fluctuate, leading to inaccurate readings. Several techniques can be used to minimize the impact of common mode noise. Using twisted-pair cabling helps to ensure that both conductors of the signal pair are equally exposed to the noise, maximizing the common mode rejection of the differential amplifier. Shielding the cable can further reduce the amount of noise that is coupled into the signal pair. A common mode choke, placed in series with the signal pair, can block common mode noise while allowing the differential signal to pass through. Ensuring proper grounding practices, such as avoiding ground loops and using a single-point ground, can also reduce common mode noise. Differential signaling rejects the noise.