Differential vs. normal probes: differences in parasitic capacitance

Differential Probes (Differential Probe) and Single-Ended Probes (Single-Ended Probe) are very different in design and use, one of which is their treatment of parasitic capacitance.

Differential probes are designed to measure the voltage difference between two points, such as differential signals or differential pairs. They typically have the following characteristics which help minimize parasitic capacitance:

1. Differential Inputs: Differential probes measure the voltage difference between two inputs instead of the voltage relative to ground. This design reduces the effect of ground loops, thus reducing parasitic capacitance due to ground.

2. Shielding: Differential probes typically have a better shielding design to minimize external electromagnetic interference (EMI) and reduce parasitic capacitance between the probe and the circuit under test.

3. Low capacitive load: Differential probes are designed to have the smallest possible capacitive load on the circuit under test, which means that the input capacitance of the probe is very low, thus reducing the effect of parasitic capacitance.

4. High impedance: Differential probes typically have a high input impedance, which helps to minimize the capacitive effects that occur when current flows through the probe.

Ordinary probes (single-ended probes) usually measure voltage relative to ground, which can lead to the following problems:

1. ground loops: single-ended probes need to be connected to ground, which can introduce ground loop problems and increase parasitic capacitance.

2. electromagnetic interference: single ended probes may be more susceptible to external electromagnetic interference, which may require more sophisticated shielding to reduce parasitic capacitance.

3. capacitive loads: single-ended probes may have a greater capacitive load on the circuit under test, which can increase the effect of parasitic capacitance.

Overall, differential probes are more effective at reducing parasitic capacitance through the specificity of their design and use, thus providing more accurate measurements, especially in high frequency and sensitive differential signal measurements.