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Derivative of output signal

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Hi All,


I'm designing some simple circuits like RLC filters and A-class amplifiers. I'm wondering how can I calculate gain by using ONLY output signal. I've notice that this can be made by using derivative operations but I'm not quite sure about that.


Regards,
E.
 

Gain is the ratio of the output signal and the input signal.
 

If the question is the terms you asked, it's not possible to estimate the gain knowing only the output signal.
Are you sure what you read was meaning exactly what you wrote ? Could you post exactly what you read about gain and derivative ?
 

I know that gain is ratio of output to input signal but as I told - I'm trying to find other way to calculate it. I'm using cadence to some simulations of CMOS inverter. I need to determine maximum DC gain of such structure and I heard that derivative of output function can be used to calculate it.
So in simple words - I'm ploting output function of amp - then I calculate derivative and in last step I'm doing 20log operation which gives me gain in dB but I don't know this method is proper.
 

In this case, I think, you have in input a signal going from 0 to 1 or viceversa. but the transition takes a finite time and can be simply modeled as a ramp.
If we imagine, for instance a signal going from -0.5V to 0.5 (so that can be inverted applying a gain) with 0.5 V offset then Vin = k*t + 0.5 where t is from 0 to the time needed to have 1 V. K is the rise time of the signal. Applying it to the inverter you will have in output Vout=G*Vin, where G is the gain of the inverter. Then

Vout = G*k*t+0.5*G taking the first derivative:

dVout/dt = G*k

if k is known the you can calculate G. In any case to know k means to know the input.
 

albbg thanks for answer.

Well I'm now confused because hmm... ok, you have analyzed this case in time domain. In cadence I have charastistic Vout=f(Vin) so... if i'll calculate derivative only of such function, I'll get gain, right ? Because I'm doing it in Vin domain.
 

Yes, as far as f(Vin) is linear.

if, for instance Vo = k*Vin + h the gain is k, while h is an offset. Deriving with respect to Vin: dVo/dVin = k
that is we recover the gain, while the offset is not taken into account
 

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