slew rate and rise time

(http://www.amplifier.cd/Tutorial/Slew_Rate/SlewRate.htm) (http://electronics.wikia.com/wiki/Amplifier#Bandwidth_and_rise_time) Click on, "bandwidth and risetime" second site. They are very similar, but not identical. These two threads should give you some insights.

Chris - slew rate is a slope of the signal going up or down expressed in V/us (rate of change). Rise time is only for known amount of volts going up (fall time for going down).

We use slew rate when voltage doesn't have any particular range of interest (output of an amp etc.) and we just want to know how fast is it changing. Another case might be when something depends, by definition, only on the rate of change - like transmission line effect.

Rise time and fall time are used mostly when voltage range is already defined like 5V logic or 3.3V logic etc.

Slew rate (as well as rise or fall time) can be applied to any analog quantity like current, resistance, light etc.

Thanks for the links and explanation guys!

Chris

Rise time is defined as the time it takes a signal to go from 10 percent of it's peak value to 90 percent of its peak value. For example, if you have a 0 to 10 volt pulse, the rise time is the time it takes for the pulse to go from 1 volt to 9 volts. For a 0 top 5 volt pulse, rise time is the time it takes the pulse to go from 0.5 volts to 4.5 volts. Fall time is similiarly defined, but in the other direction. Rise and fall times are just that, time measurements specified by a single unit. Slew rate is a units per time (eg. volts per time) measurement, specified with two units; eg. volts / time.

Slew rate is typically used to describe an amplifier (look at a spec sheet for an op amp). Rise and fall times are typically used describe signals.

One more point as far as interrelationships. If it is not already obvious from the previous posts, if you are using an amplifier to process pulses you would first determine the rise time and fall time of the fastest changing pulse and the change in volts of that pulse, that you expect to encounter and then select your active devices based on that time. That is a starting point. In many instances the passive components that you select and the pcb layout and physical construction may also need to be considered, depending on those times.