Detailed explanation of oscilloscope probe

Oscilloscope probes are generally divided into passive probes 、 Active probe 、 Current probe
One 、 Passive probe
Passive probes are divided into 1×,10×,100× And other specifications ,10× It means that the probe will attenuate the signal ten times , After connecting to the oscilloscope
The oscilloscope is required to amplify the corresponding channel 10 times . The figure below 1 It's a 10× Internal equivalent structure diagram of passive probe

Passive probes are divided into 1×,10×,100× And other specifications ,10× It means that the probe will attenuate the signal ten times , After connecting to the oscilloscope
The oscilloscope is required to amplify the corresponding channel 10 times . The figure below 19 It's a 10× Internal equivalent structure diagram of passive probe
Oscilloscope input grounding resistance Rs by 1M ohm ,10× Probe in series I 9M Ohm resistance Rp, The two resistance partial voltage makes the signal input to the oscilloscope equal to the amplitude of the measured signal 1/10.
It can be seen that the oscilloscope has an input capacitor Cscope, There is a and input on the probe 9M Capacitance with ohmic resistance in parallel （ Make it Cp）, There is also an adjustable capacitor connected in parallel to the ground Ccomp. The attenuation of the probe is constant over a wide frequency range 10, Need to make （Ccomp+Cscope）/Cp=9, Compensation capacitance Ccomp Adjustable .
When connecting a newly bought probe to the oscilloscope , The compensation capacitance needs to be adjusted Ccomp Value , Make the relation （Ccomp+Cscope）/Cp=9 establish . chart 19 The second line of is the result of different compensation capacitance values , When compensation is not paid （Ccomp+Cscope）/Cp>9, The attenuation value of the high-frequency component of the measured signal is greater than 10 times , And there is still only 10 Zoom in , As a result, the attenuation of the oscilloscope to the high-frequency component is greater than that to the low-frequency component . The principle of over compensation is the same . The third picture is the best compensation result .
100× The probe is similar to 10× Probe ,1× The probe is equivalent to a straight line , Input the signal directly to the oscilloscope . The probe with large attenuation can measure higher voltage , The probe with small attenuation is suitable for measuring small voltage .1× Probe input impedance is low （1M）, And the input capacitance is large , Therefore, the bandwidth is small . What we use most is 10× Probe .
Two 、 Active probe
There are only some resistors inside the passive probe , Capacitors and other passive components . The active probe contains an amplifier , The amplifier needs power to work , Therefore, it becomes an active probe . chart 20 Is the structure diagram of active probe , The amplifier in the probe can ensure that the input impedance is large enough , The output capacity is very strong , Can directly drive 50 ohm . And the input capacitance of the amplifier can be very low , Less than 1pf, Therefore, the bandwidth of the active probe can be several G.
The disadvantage of the active probe is that its withstand voltage ability is only tens of volts , The passive probe can input 300V RMS High voltage . Be very careful when using the active probe , Protect the probe from overload .

3、 ... and 、 Current probe
The current probe is essentially a current and voltage sensor , Because the oscilloscope can only measure voltage , The probe is required to convert current into voltage .
chart 3 Is the internal block diagram of the current probe . measurement DC To dozens of K In the low frequency range , Use Hall effect , Measure dozens K Above high frequency
Current use transformer .