How to measure voltage rise delay and fall delay?

In summary: You can measure it by looking for the points where the waveforms cross 1.5 volts. For rising waveforms, it should be at the 10% point, and for falling waveforms it should be at the 90% point.
  • #1
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In Cadence we built a CMOS inverter. I made a transient response graph showing the input and output voltage waveforms. We're supposed to measure rise delay and fall delay of the output voltage. How do I do this? I heard from someone else that it's where the graphs cross 1.5V, but I'm still not exactly sure how to measure it.
 
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  • #2
6021023 said:
In Cadence we built a CMOS inverter. I made a transient response graph showing the input and output voltage waveforms. We're supposed to measure rise delay and fall delay of the output voltage. How do I do this? I heard from someone else that it's where the graphs cross 1.5V, but I'm still not exactly sure how to measure it.

The rise and fall times are usually measured between the 10% and 90% points on the waveform. That is, the time between when the waveform makes it to 0.1Vdd and to 0.9Vdd for the rising edge, and similarly on the falling edge.

This paper (found with googling CMOS Inverter Risetime) has a nice treatment in general of CMOS inverter design:

http://www.ee.mut.ac.th/home/theerayod/lecture_files/EEET0413/Lecture 4 - CMOS Inverter.pdf

.
 
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  • #3
We're supposed to measure rise delay and fall delay of the output voltage.

This is a bit ambiguous. It could mean the propagation delay through the inverter or it could mean the rise and fall times of the output waveform.

So, I'll cover both.

See this diagram:
delays.PNG


The two waveforms at the left are the input (top) and output (bottom) as viewed on a dual trace oscilloscope. The output will be delayed slightly due to the internal operation of the inverter chip. You measure this on any reasonably vertical portion of both waveforms provided it is the equivalent point on each graph, allowing for the inverting action of the inverter..
This is just to avoid errors due to rounded corners etc.

Rise and fall times are the times it takes for the waveforms to go from 10 % of the full amplitude to 90 % of full amplitude (or the other way around for falling waveforms).
This is shown on the right two diagrams.
 

FAQ: How to measure voltage rise delay and fall delay?

What is voltage rise delay and fall delay?

Voltage rise delay and fall delay are two important parameters used to measure the response time of a circuit. They refer to the time it takes for the output voltage to reach a certain percentage of its final value after a change in the input voltage.

How is voltage rise delay and fall delay measured?

Voltage rise delay and fall delay can be measured by applying a step input voltage to the circuit and measuring the time it takes for the output voltage to reach a specific threshold, usually 10% or 90% of its final value. This can be done using an oscilloscope or a specialized voltage rise and fall delay measurement instrument.

What factors can affect voltage rise delay and fall delay?

There are several factors that can affect voltage rise delay and fall delay, such as the capacitance and resistance of the circuit, the type and quality of components used, and the temperature. These factors can cause variations in the response time of the circuit and should be taken into consideration during measurement.

Why is measuring voltage rise delay and fall delay important?

Measuring voltage rise delay and fall delay is important for ensuring the proper functioning of a circuit. It helps to determine the speed and accuracy of the circuit's response to changes in input voltage, which is crucial in many applications such as communication systems, digital circuits, and power electronics.

Are there any industry standards for measuring voltage rise delay and fall delay?

Yes, there are industry standards such as JEDEC JESD 51-3 and IEEE 1547.1 that provide guidelines for measuring voltage rise delay and fall delay. These standards specify the test conditions, equipment, and measurement methods to ensure accurate and consistent results.

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