Measurements on buffer and weird output waveform

Discussion in 'General Electronics Chat' started by luma, Jan 29, 2016.

  1. luma

    Thread Starter Member

    Nov 5, 2015
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    Hi guys, here again, As you can remember from the other post I wanted to understand what's wrong in the circuit (CMOS buffer or push pull amplifier) attached.
    Most of you gave me good suggestions to make it work. However before to give up with that buffer I wanted to check for real if that buffer I proposed cannot really work and how it behaves. I built the circuit by using the typical CD4007 and creating a buffer . In the attachment I wrote the number of pins and the signals.
    My test consisted to bias the input of the buffer with a voltage around 5V and check what happen if I increase the input voltage of the signal. This test could give me some info about what is the caratteristc curve (vo/vin) of the buffer. However the output seems to be distorted by the buffer and I don't get why.
    I attached some pictures about measurements with oscilloscope. the green line is the input, the yellow line is the output.
    Anyone can explain me what happen when I increase the amplitude of the input signal? And why there is a distortion?
     
  2. nigelwright7557

    Senior Member

    May 10, 2008
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    You are getting crossover distortion.
    You need a Vgs multiplier before output transistors.
     
  3. Jony130

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    Feb 17, 2009
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    Last edited: Jan 29, 2016
  4. Jony130

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    But TS is using CD4007
     
  5. dl324

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    Mar 30, 2015
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    You show an impossible, and incorrect, bulk connection. As you also did in your other thread...
     
  6. luma

    Thread Starter Member

    Nov 5, 2015
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    Thank you very much for all your answer, however
    thanks for your answer, however what I built is an analogue circut not digital, indeed is a push pull amplifier , not an inverter
     
  7. luma

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    Nov 5, 2015
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    What do you mean? How would you connect the bulk of the mosfet?
     
  8. dl324

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    The bulk of a PMOS device is normally connected to the positive supply and the bulk of the NMOS device is normally connected to the negative supply. In the CD4007, those connections are already made and can't be changed.
     
  9. Jony130

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    PIN 14 to VDD and pin 7 to GND. Also a push pull amplifier do not provide any voltage gain .
     
  10. luma

    Thread Starter Member

    Nov 5, 2015
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    Thanks for your comment, however as is shown in the schematic the bulk are connected as you said. Look better . Second : the bulks on the CD4007 available externally and not internally connected. Look better to the datasheet.
    (p.s in my schematic I forgot to draw the number of the pin for the bulks but the bulk of NMOS is 7 top GND and the bulk of PMOS is 14 to VDD)
     
  11. luma

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    Nov 5, 2015
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    Thank you jony for your answer can you quote, the question, otherwise i cannot understand to which question or sentence you are answering.
     
  12. dl324

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    You need to follow your own advice. In your schematic, you show the connections backwards. The bulk of the PMOS is connected to 0V and the bulk of the NMOS is connected to 10V.
     
  13. luma

    Thread Starter Member

    Nov 5, 2015
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    Photo 29-01-16 16 22 42.jpg

    AND if you see carefully also in my previous thread the bulk are connected correctly
     
  14. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Which connections did you use?

    4007_connections.png

    In the datasheet there is this given for biasing:

    4007_bias.png

    I have also attached the PDF that contains the shown images.

    Bertus
     
  15. luma

    Thread Starter Member

    Nov 5, 2015
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    thank you for your answer the pin i m using are drawed in my schematic, please check there, however is the second pair of mosfet in the image you post it.
    The schematic you show and suggested by the company is just for na inverter while
    i built a push pull amplifier
     
  16. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Why do you post the pictures on its side?
    I will NOT turn my monitor to view the image !
    It can easily be corrected using any kind of paint program:

    Luma_inverter.jpg

    Bertus
     
  17. dl324

    Distinguished Member

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    What you've labeled as NMOS is the PMOS device.

    EDIT: Based on the non-standard symbols you're using.
     
  18. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You WILL need the bias to avoid the cross-over distortion.
    It IS an amplifier as shown.

    Bertus
     
  19. luma

    Thread Starter Member

    Nov 5, 2015
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    my apologies
     
  20. luma

    Thread Starter Member

    Nov 5, 2015
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    Please check the number of the pin.
     
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