Simple question! magnitude vs. amplitude

[sabiram164]

Simple question!

If you consider sin wave: we have ac magnitude and ac amplitude . Whats the difference between them.

So when I give a sin wave to amplifier : what gets amplified, is it the ac magnitude or ac amplitude.

Thank you!

 

[sunderwood]

Re: Simple question!

I believe they are the same thing (peak value).
In A x sin(wt), A is the magnitude/amplitude.
If you have a sine wave and feed it to an amplifier, you will increase its amplitude (or magnitude), and possibly get a phase shift.
Regards,

 

[sabiram164]

Re: Simple question!

Hi! Thank you replying. But if you take a sin wave component in cadence software we could see phase, DC voltage, offset, ac magnitude, ac amplitude . What does this mean.

I then constructed a Differential amplifier with sin wave as input. I gave the following details : dcvoltage : 500mV, offset : 0, phase 0, ac magnitude : 500mV , ac amplitude : 500mV. When I simulated I could see that ac magnitude being amplified to 20 V or something and the amplitude amplified to 2V. This bothers me! Thank you!

 

[cmoseye]

Simple question!

I have a question that how do you see the output ac amplotude signal.
Are you sure the param is ac amplitude? I think it is used for sin wave like this:
Vsin=amplitude*sin(ft).if you don't set frequency f , then f=0 in default value and hence Vsin=0.

 

[eem2am]

Re: Simple question!

well magnitude usually refers to a scalar quantity.

amplitude....this could be a vector i suppose.

With scalar we do not talk of phase.

so amplitude could be amplitude relative to some refeence signal.

think of three phase........phase A has an magnitude at its peak as that value relative to earth gnd.

but at this time, its amplitude relative to one of the other phases is different

 

[maheshkuruganti]

Re: Simple question!

Unless I am mistaken amplitude is defined as maximum deviation from a mean point.So It is the Peak Value.Magnitude on the other hand may be either the Peak to Peak Voltage or RMS .But by no calculation is your output correlating to the definitions

 

[LvW]

Re: Simple question!

I think both expressions (amplitude resp. magnitude) are related and similar - and very often are mixed.
For example, in most simulation programs the expression "amplitude" is used to describe a sine wave in the time domain and is identical to the peak value. In contrast, the word "magnitude" is used mostly in the frequency domain for the rms value of a sine wave - together with the corresponding phase information. But it´s a matter of convention.

 

[saruman1983]

Re: Simple question!

AC amplitude and AC magnitude are physically the same thing. Distinction is made by simulation programs when running AC or transient analysis respectively. In AC analysis the circuits characteristics are being linearized around the DC operating point and AC amplitude is used to calculate the outputs in the frequency domain. In transient analysis there is no linearization and the outputs which are now produced in the time domain contain every information of the behavior of the circuit (like distortion). The linearization being applied in the AC analysis means that the AC magnitude can assume any value, no matter how large, while a large applied AC amplitude in a transient analysis would produce a number of artifacts.

P.S. In most simulation programs there exists the Harmonic Balance simulation to calculate distortion in the frequency domain too

Added after 3 minutes:

(To avoid confusion AC magnitude ---> AC analysis
AC amplitude ---> transient analysis)

 

[santom]

Re: Simple question!

Thanks for the valuable question and respective answers..!

Regards
Santom

Added after 4 minutes:

AC amplitude and AC magnitude are physically the same thing. Distinction is made by simulation programs when running AC or transient analysis respectively. In AC analysis the circuits characteristics are being linearized around the DC operating point and AC amplitude is used to calculate the outputs in the frequency domain. In transient analysis there is no linearization and the outputs which are now produced in the time domain contain every information of the behavior of the circuit (like distortion). The linearization being applied in the AC analysis means that the AC magnitude can assume any value, no matter how large, while a large applied AC amplitude in a transient analysis would produce a number of artifacts.

P.S. In most simulation programs there exists the Harmonic Balance simulation to calculate distortion in the frequency domain too

Added after 3 minutes:

(To avoid confusion AC magnitude ---> AC analysis
AC amplitude ---> transient analysis)

the underlined word should be actually AC magnitude I guess..!

Regards
Santom

 

[Haihua Xu]

Re: Simple question!

The “vsin” symbol has many properties: “acm” is “AC Magnitude”, the amplitude of the AC signal applied
to the linearized circuit (small signal circuit) during an AC Analysis. The “acp” is the “AC Phase”, “vo”
refers to “DC Offset”, and “vm” refers to “Amplitude”, the amplitude of the signal applied to the largesignal
(non-linear) circuit during a Transient Analysis.