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  1. #1
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    How to measure THD and gain in cadence 6.1.4

    Hello everyone,

    I have designed OTA for hearing aid application. I want to measure THD of OTA. How can i measure it?

    The value that i get is it in percentage or not?

    Another query is that gain of the OTA is the ratio of output current to input voltage or ratio of output voltage to input voltage?

    please help me i am too confused becoz i have calculated as ratio of output voltage to input voltage, but i got it negative dB value.

    And also tell me what is the possible value of gain for OTA of hearing aid application?

    plz, help me........... thanks in advance.........

    •   Alt23rd April 2012, 15:47

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  2. #2
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    Re: How to measure THD and gain in cadence 6.1.4

    hi
    output current to input voltage,
    for THD calc have a look at
    http://www.edaboard.com/thread127782.html

    Regards



    •   Alt23rd April 2012, 16:19

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  3. #3
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    Re: How to measure THD and gain in cadence 6.1.4

    Thanks a lot..........
    How to plot the gain plot of OTA in CADENCE spectre? is it frequency Vs. ratio of output current to input voltage? please help me......
    After taking dB20 and phase(degree) of this plot can i get gain, phase, pahse margin and gain margin?
    please help me i want to find these parameters....
    Thanks in advance



    •   Alt23rd April 2012, 17:35

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  4. #4
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    Re: How to measure THD and gain in cadence 6.1.4

    yes, add input signal to design in testbench view as Vcm and diff signal on top of it, ( simply connect vdiff to pos input of ota with mag of 1, and vcvs with gain of -1 to neg input,) and then run your ac simulation. Ofcourse instead of selecting Vout as in amp u should select Iout .
    from the resulting plots (ac simulation result ) u get what u need



  5. #5
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    Re: How to measure THD and gain in cadence 6.1.4

    sir, i cant understand.... i have done it but still i get negative dB response..........
    I have attached OTA design please guide me...... i really need it....
    Click image for larger version. 

Name:	prog_OTA.png 
Views:	25 
Size:	156.6 KB 
ID:	73101
    Thanks in advance...



    •   Alt24th April 2012, 10:33

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  6. #6
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    Re: How to measure THD and gain in cadence 6.1.4

    Hi
    I have a similar inquiry wherein I have a CMOS OTA and I have to plot its THD in Cadence Spectre.

    I have done parametric analysis in several frequency steps and then when I went to calculator and filled in all 4 parameters and clicked THD in special functions it simply gave me a scalar value.

    But I want to plot THD graph with 5 tones plus fundamental while calculator takes only one frequency at a time.

    Is there any other method of calculating THD without using calculator?

    Pl help....thanks



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