linearity measurement using transient analysis

[nisha gupta]

hi
can any1 tell how to do linearity measurement of an amplifier using transient analysis.
i hv done it using PSS analysis. but somebody told me it can be done by transient analysis also. i did'nt understand exactly... hw it is possible.
plz help me.

 

[erikl]

You can measure linearity vs. input common mode range (ICMR) @ a fixed ac input voltage, i.e. you alter the DC ICM voltage over time and measure the gain vs. the ICMR, or you measure linearity vs. ac input voltage value, i.e. you alter the ac input voltage level over time (@ fixed DC ICM voltage) and measure the gain vs. ac input voltage level, both within a transient analysis run, of course.

 

[LvW]

I am not sure, if the method as mentioned by erikl really works - because: Gain is defined for signals of the same shape (input and output).
And exactly THIS condition is not fulfilled if we have distortions caused by non-linearities.

If you are required to determine the non-linearity as a value you must know how non-linearity is defined (THD).
This definition leads to the corresponding measurement procedure based on a FOURIER decomposition of the output signal for a sinusoidal input signal (time domain).

 

[crutschow]

If you input a voltage ramp and plot the gain (output / input) using the transient analysis, that will give a measure of the linearity.

 

[albbg]

If you input a voltage ramp and plot the gain (output / input) using the transient analysis, that will give a measure of the linearity.

This can be applied only to a DC amplifier (for instance a DC-coupled op-amp) and the result will be valid only to that case. You could, instead, apply a sinewave at a given frequency, increase its level as a ramp and plot the gain as OtputLevel/InputLevel.

 

[crutschow]

This can be applied only to a DC amplifier (for instance a DC-coupled op-amp) and the result will be valid only to that case.................

It can be used with an AC amp if you use a repetitive ramp and the repetition rate is such that the Fourier frequencies of the ramp are well within the bandwidth of the amplifier.

 

[nisha gupta]

in transient analysis all the plots will be with respect to frequency. how can i get input vs output plot... using transient..

 

[LvW]

in transient analysis all the plots will be with respect to frequency. how can i get input vs output plot... using transient..

No - in transient analysis, all plots will be with respect to time.

 

[nisha gupta]

ya i mean to say that only.... actually i want to ask how can i plot (output/input) plot using transient analysis...

 

[crutschow]

What simulation program are you using? Doesn't it perform waveform calculations?

 

[nisha gupta]

i m doing transient simulation using cadence virtuoso... actually after taking output net /input net plot, it is giving somthg like ECG signal not like ramp....... plz suggest me why it is cmng ........or m i doing smthg wrong..

 

[crutschow]

Post the circuit diagram and the plots.

 

[bernhard8]

You can apply a sine wave at the input, do a transient simulation and a FFT of the output and consider the input frequency and all harmonics. At the end it's more complicated than SpectreRF's small signal methods.