1
\$\begingroup\$

The analog front end of an oscilloscope begins with an attenuation stage. Mostly they use two attenuation stages, like 1/1 and 1/50.

enter image description here From: Rigol Homebrew Wiki - schematics page

The image above belongs to an oscilloscope AFE. Here, a relay sets the attenuation. The attenuation is in the stage of 1/1 in the picture. After the relay and a 330 pF capacitor there is a clipper diode stage.

When the frequency increases, the reactance of the capacitor decreases. When a 50 MHz signal is applied the reactance is 9.64 Ω.

How can clippers stands a 20 Vpp, high-current, 50 MHz signal? What is protecting the +5 V and -5 V lines from the input signal? And how does this protect semiconductors?

\$\endgroup\$
16
  • 2
    \$\begingroup\$ Does the product spec say it will tolerate said overload without damage? \$\endgroup\$
    – Kartman
    Commented Dec 26, 2023 at 17:50
  • 1
    \$\begingroup\$ @Kartman it is not clear in the specs. I guess a signal 20Vpp and 50MHz which has enough power to overload clippers is very rare so they dont care much? i dont know \$\endgroup\$
    – Ahmet Atcı
    Commented Dec 26, 2023 at 18:04
  • 2
    \$\begingroup\$ @Kartman the Rigol DS1052E datasheet does not. It only lists a maximum input voltage of 400 V DC + AC, and a measurement category of CAT I 300Vrms, 1000Vpk / CAT II 100Vrms, 1000Vpk. The user manual doesn't go into more detail either. There is no frequency dependent voltage de-rating curve, nor are there different ratings for different input settings. There is a separate 40 V DC + AC rating, but that's for the logic analyzer inputs \$\endgroup\$
    – jms
    Commented Dec 26, 2023 at 18:20
  • 1
    \$\begingroup\$ @AhmetAtcı You missed that essential part in the question: "I am designing a litte oscilloscope so I want to have enough protection for the inputs." Also, you did not define "enough protection." Please think about how much information we need to begin to help you. \$\endgroup\$
    – Andrew Morton
    Commented Dec 26, 2023 at 19:17
  • 3
    \$\begingroup\$ Why is this getting multiple close votes "questions on the use of electronic devices are off-topic"? OP is clearly trying to understand the rationale behind design decisions in a commercial product in order to better design his own. At no point has OP asked how to use an oscilloscope, or what kind of signal can be fed into the inputs without damage. OP has simply seen that the specs don't match with the limitations implicit in the circuit, and is asking why. I can understand closing the question on a different basis, but the "questions about use" rationale doesn't make any sense. \$\endgroup\$
    – jms
    Commented Dec 26, 2023 at 19:44

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.