# Cut off frequecy and amplitude of a signal

Discussion in 'General Electronics Chat' started by gotumal, Jun 3, 2009.

1. ### gotumal Thread Starter Active Member

Mar 24, 2008
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0

I was wondering regarding the frequency and amplitude of a signal, viz sine wave. I think the frequency parameter should always specific to voltage.

While defing the frequency responce (analysis) of any device, the basic component considered is a sine wave. Which is nothing but a specific rate of change of voltage withing a given time.

For instance, for a low pass filter, cut-off frequency Fc is defined irrespective of amplitde. So it can pass all frequencies below Fc say with an amplitude V. So if the amplitude of signal is reduced to V', principly the signal of frequency more than Fc should be passed since the rate of change of voltage is less than what was there with earlier signal of amplitude V.

Is that so? In OPAMP theory this term is very weel defined by slew rate but not in any other frequecy terms like cut off frequencies etc.

2. ### Audioguru Expert

Dec 20, 2007
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1,212
The cutoff frequency occurs when the output level has dropped -3dB from the flat level. -3dB is half the power.

3. ### gotumal Thread Starter Active Member

Mar 24, 2008
99
0
Thanks Audioguru,

Actually I am designing a ciruit to read a static gravity and vibrations from the same IC. One needs precise static characteristics (stable DC) whilst the other should be dynamic (voltage indicates rate of change of velocity (or acceleration) at that time). I was not not sure how to accomodate both in a single circuit. So lead to confusion with my basics!

Thanks once again.