Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics
Linux Systems
Linux Systems
Power Users
Power Users
Tabletop RPGs
Tabletop RPGs
Community Proposals
Community Proposals
tag:snake search within a tag
answers:0 unanswered questions
user:xxxx search by author id
score:0.5 posts with 0.5+ score
"snake oil" exact phrase
votes:4 posts with 4+ votes
created:<1w created < 1 week ago
post_type:xxxx type of post
Search help
Notifications
Mark all as read See all your notifications »
Q&A

How do we calculate signal rise time from frequency

+0
−1

May I know how to calculate a signals rise time from it's frequency.

I found this article for the same.

The formula given is Tr = 1/f*π.

May I know is this applicable for PWM also.

History
Why does this post require attention from curators or moderators?
You might want to add some details to your flag.
Why should this post be closed?

0 comment threads

1 answer

+1
−0

Your question is ambiguous.

First, you need to define "rise time". That applies to a step, not a periodic signal. Let's say you have a 0 to 5 V digital signal. The rise time is how long it takes to go from the low state to the high state.

However, that is still ambiguous. Let's say the signal goes thru a single-pole filter, like a resistor followed by a capacitor to ground. In theory, the output never fully gets to the 5 V level. Do you need it to get 90% of the way? 99%? 99.99%?

For a digital signal, you might consider the rise time to be from when the signal first exceeds the maximum guaranteed logic low input level to when it first reaches the minimum guaranteed logic high input level. In other cases, "rise time" might mean the time to get from 10% to 90% of the final value, or some other fixed thresholds. It depends on the application and what characteristics of the signal you actually care about.

Your question is further confusing because it wants to relate this to frequency. Rise time is a single step-response event. Frequency implies something periodic. It's not clear what you are envisioning.

For a pure frequency, which is a sine wave, you could argue that the "rise time" is the part of the waveform where the signal is rising. That's half the period, so 1/2f in seconds when f is the frequency in Hz.

A more reasonable question would be how rise time relates to bandwidth, but that's not what you asked. Or, you could ask about the xx% to yy% rise time of a step after a single-pole filter of a particular rolloff frequency. That can actually be answered and the result meaningful, but it is also getting rather far from what you asked.

History
Why does this post require attention from curators or moderators?
You might want to add some details to your flag.

1 comment thread

Yes. In particular, a huge range of frequencies often produce practically the same rise time. (1 comment)

Sign up to answer this question »