Help with RLC Circuit Oscilloscope Probe - Calculating Voltage Spike

In summary, the conversation discusses the modeling of an oscilloscope probe and how to calculate voltage spikes caused by inductance. It is mentioned that using a 50 ohm resistor and coax cable may yield better results than an active probe. There is also a question about the opposition of change by inductors in a series circuit.
  • #1
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I am trying to model an oscilloscope probe(active probe).

The voltage source in the circuit is from the device under measurement.
Let's say a 100MHz clock.
The probe signal and ground lead inductance are represented by 2 inductors, then a small series resistor. I made up the value of the series resistor.
The input capacitance is 1pF and resistance is 1M.

How do I calculate the voltage spike (overshoot) caused because of the inductance?

Another question - when the signal rises from 0 to 5v, the inductor L1 opposes the change. When the current reaches L2, does L2 also oppose the change?
 

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  • #2
Anybody?
 
  • #3
R1 is 2.00M, if it is left out there would be very little effect on the circuit.

With R1 removed, this is a simple series circuit and should be easy to analyize.

Bob Pease of National Semiconductor wrote an article about using a 50 ohm (or maybe it was 75 ohm) resistor and coax as a probe for an oscilloscope. He had better results than using an active probe.
If you are unable to locate the article with Google, I will check to see if I have it on file.

"Another question - when the signal rises from 0 to 5v, the inductor L1 opposes the change. When the current reaches L2, does L2 also oppose the change? "
The two inductors are in series, so the current goes through them at the same time.

Good Luck
Carl
 

1. How do I calculate the voltage spike in an RLC circuit using an oscilloscope probe?

To calculate the voltage spike in an RLC circuit using an oscilloscope probe, you will need to measure the amplitude of the voltage spike using the oscilloscope, as well as the frequency of the oscillations. Next, you will need to plug these values into the formula V = IωRC, where V is the voltage spike, I is the current, ω is the angular frequency, R is the resistance, and C is the capacitance. This will give you the voltage spike in the circuit.

2. What is the purpose of using an oscilloscope probe in an RLC circuit?

An oscilloscope probe is used in an RLC circuit to accurately measure the voltage at different points in the circuit. It allows for more precise measurements and can help identify any voltage spikes or oscillations that may occur.

3. How does the RLC circuit affect the voltage spike?

The RLC circuit affects the voltage spike by regulating the flow of current in the circuit. The resistance, inductance, and capacitance values in the circuit determine how quickly the voltage spike occurs, how high it reaches, and how long it lasts. A higher resistance will result in a lower voltage spike, while a higher capacitance will result in a higher voltage spike.

4. Can the voltage spike in an RLC circuit be controlled?

Yes, the voltage spike in an RLC circuit can be controlled by adjusting the values of resistance, inductance, and capacitance in the circuit. By changing these values, you can alter the frequency, amplitude, and duration of the voltage spike.

5. What is the significance of measuring the voltage spike in an RLC circuit?

Measuring the voltage spike in an RLC circuit is important because it can help identify any potential issues or malfunctions in the circuit. It can also provide valuable information about the behavior and characteristics of the circuit, which can be used for further analysis and improvement.

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