The difference between high voltage probes and differential probes

The high-voltage probe has an attenuation ratio of 1:10, 1:100, 1:1000, etc. When the signal is connected to an oscilloscope, multimeter, computer, etc., because of the above equipment, the voltage must be attenuated through the high-voltage probe (just the voltage is reduced Only when the other parameters remain unchanged) can it be accurately tested within the measurable range of the equipment.

A differential probe is a measurement probe of an oscilloscope. Differential probes have therefore become a mainstream accessory for modern oscilloscopes.

Differential measurement features:

Probes can be generally divided into two types: passive probes and active probes. Users of wide-bandwidth oscilloscopes and active probes also need to make a choice between single-ended probes and differential probes. The pair of traces that carry differential signals is called a differential trace. This article mainly talks about differential probes. Compared with ordinary single-ended signal wiring, the most obvious advantages of differential signals are reflected in the following three aspects:

1. Strong anti-interference ability, because the coupling between the two differential traces is very good. When there is noise interference from the outside, it is coupled to the two lines almost at the same time, and the receiving end only cares about the difference between the two signals. Therefore, external common mode noise can be offset to the greatest extent.

2. It can effectively suppress EMI. In the same way, since the polarity of the two signals is opposite, the electromagnetic fields radiated by them can cancel each other out. The closer the coupling, the less electromagnetic energy released to the outside world.

3. Accurate timing positioning. Since the switching change of the differential signal is located at the intersection of the two signals, unlike ordinary single-ended signals that rely on high and low threshold voltages to judge, it is less affected by process and temperature, and can reduce timing errors. , and it is also more suitable for circuits with low amplitude signals. The currently popular LVDS refers to this small amplitude differential signaling technology.

The structural characteristics of differential signals require that the corresponding test equipment must also be a differential topology. Therefore, differential probes have become a mainstream accessory of modern oscilloscopes.

working principle:

The principle of differential amplification means that a pair of signals are input into the amplification circuit at the same time, and then subtracted to obtain the original signal. A differential amplifier is an amplifier composed of two transistors with the same parameters and characteristics using direct coupling. If signals of the same magnitude and phase are input to the two input terminals, the output will be zero, thereby overcoming the zero point drift.

Basic differential amplifier circuit diagram, bias parameters not shown. Q1 and Q2 are transistors with the same parameters. Signals are input from the bases of Q1 and Q2 at the same time and output from the collector. The obtained signal is the differentially amplified signal.