Types and working principles of oscilloscope probes
Most people will pay more attention to the use of the oscilloscope itself, but ignore the selection of probes. In fact, the probe is the intermediate link between the signal under test and the oscilloscope. If the signal is already distorted at the probe, then it is useless no matter how good the oscilloscope is. In fact, the design of the probe is much more difficult than that of the oscilloscope, because the oscilloscope can be well shielded internally and does not need to be disassembled frequently. In addition to meeting the convenience requirements of detection, the probe must also ensure at least the same bandwidth as the oscilloscope. Much more difficult. Therefore, when the earliest high-bandwidth real-time oscilloscopes first appeared, they did not have corresponding probes, and it took a while for the probes to come out.
To choose the right probe, the first thing to do is to understand the impact of the probe on the test, which includes:
1. The influence of the probe on the circuit under test;
2. Signal distortion caused by the probe. The ideal probe should have no impact on the circuit under test and no distortion on the signal. Unfortunately, no true probe can satisfy both of these conditions, and some compromise between these two parameters is usually required.
For DC or general low-frequency signals, the oscilloscope probe is just a section of transmission cable formed by a specific impedance R. As the frequency of the signal to be measured increases and becomes irregular, the oscilloscope probe will introduce parasitic capacitance C and inductance L during the measurement process. The parasitic capacitance will attenuate the high-frequency component of the signal and slow down the rising edge of the signal. Parasitic inductance will form a resonant circuit together with parasitic capacitance, causing the signal to resonate. All of this creates challenges with the accuracy of our measured signals.
