I want to calculate the THD in cadence??

[muffassir]

Hi all;



I want to calculate the total harmonic distortion (%) of my analog circuit.. I have two inputs as Vx and Vy ..Wherein i want to plot the THD variation due to input voltage swing between 0 and 1.8V(instead of 2.5V as shown in the pic called THD) while Vx set to different DC values.

I want the waveform like this(only tech is different that is here it is 350nm and i am using 180nm )



My input are two i.e. Vx and Vy,
Vx
Dc Voltage=0V
AC Mag=1.8
Amplitude =5m
Freq=10KHz.

Vy

Dc Voltage=0V
AC Mag=1.8
Amplitude =5m
Freq=300KHz.

The circuit is a multiplier circuit. and output is Current.

The input trans analysis is as below and the output is also below.






Please specify what fields i have to fill(the value) step by step ..and how can i draw the THD% Vs Vy as shown in first fig.


How can i do that in cadence . I am using Cadence 6.1.4.500 and ADE L . and gpdk180.



Thanks in advance..

 

[erikl]

See this thread, especially laoud's recommendation (#2). And perhaps this PDF may be helpful: View attachment method_of_obtaining_THD.pdf

 

[steadymind]

you have to measure as mentioned by erikl.
the figure you have posted needs post processing of data from cadence. calculate the thd for each given case vx = 0,1,2 ; vy = 0,1,2; etc. then create a table in excel or similar tool and plot the thd% vs vy for varying vx. i would suggest writing a script to run sim and compute result.

 

[muffassir]

See this thread, especially laoud's recommendation (#2). And perhaps this PDF may be helpful: View attachment 66001

Thanks erikl,

I followed the pdf and calculated the THD=74.11
Is this value is correct(any interpretation??) and is it in percentage or real value..From the past threads t i see that this value is real if i am not wrong .

I measured the THD for Vy input which has 300KHz frequency .The start time i gave for the last cycle from 95us to 100us (pl.see the fig in the 1st post) and fundamental freq=0.

Further i am not able to see the erplot button in my calculator to plot the buffer output.(as mentioned in the pdf).

---------- Post added at 15:21 ---------- Previous post was at 14:09 ----------

you have to measure as mentioned by erikl.
the figure you have posted needs post processing of data from cadence. calculate the thd for each given case vx = 0,1,2 ; vy = 0,1,2; etc. then create a table in excel or similar tool and plot the thd% vs vy for varying vx. i would suggest writing a script to run sim and compute result.

Hey i am new to Analog. Can u please say me what i should vary..DC voltage or AC Magnitude.or Amplitude of the Vsin inputs Vx and vy? and how they effect the THD?

 

[erikl]

... i am not able to see the erplot button in my calculator to plot the buffer output.(as mentioned in the pdf).

May be it's not available in your version. The a.m. PDF, however, suggests:

4. Click print in the waveform calculator.

 

[steadymind]

your fundamental frequency from post#1 is 10khz not zero. redo the thd with 10khz. if freq is 0 then you are looking for dc which is why you get 75.

 

[nazhaahai]

Then I want to simulate the THD+N using spectre，who can help me .

---------- Post added at 11:14 ---------- Previous post was at 09:47 ----------

according for method_of_obtaining_THD.pdf,I calculated the THD=48.986,it is right?

 

[steadymind]

@ nazhaahai -- That pdf has the method to calculate THD, its hard for to say whether your answer is right.