Improving rising and falling time of AD8561

Discussion in 'Analog & Mixed-Signal Design' started by m.serdar, Sep 23, 2016.

  1. m.serdar

    Thread Starter New Member

    Sep 23, 2016
    3
    0
    Hello. I tried a basic circuit with AD8561 comparator. The circuits and the output is under this post. I wonder that if this 800us rising and falling time can be reduce or not. Thanks in advance! yükselme zamanında gecikme.jpg
     
  2. ci139

    Member

    Jul 11, 2016
    341
    38
  3. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    2,689
    2,750
    From the datasheet:

    Rise Time 20% to 80% 3.8 ns
    Fall Time 80% to 20% 1.5 ns

    You are doing something wrong.
     
  4. m.serdar

    Thread Starter New Member

    Sep 23, 2016
    3
    0
    Dear joeyd999, yes i read the datasheet...Can you see the wrong?
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,028
    3,237
    Your simulation appears to be way off.
    Even with such a slow input slew rate, the output rise/fall times should be well below 100μs.
    Try reducing the Maximum Timestep to 100ns.
    Also try a higher input frequency (such as 100kHz) and see if that makes a difference.
     
  6. ci139

    Member

    Jul 11, 2016
    341
    38
    what are you exactly measuring on your schematic o_O
    ? the scope ports (ups! - sorry now i see it G CH1 CH2)
    LT Spice ↓↓↓ "thinks"
    _Draft-AD-comp-E00.png
    (((? the digital ground -- pin 6 - is not specified in datasheet -- must dig it out from the web . . . digging . . . seems smth I/O signal chains unbound de-couple ? with common Vcc . . . am i loosing it ??? ))))
    http://www.analog.com/media/en/technical-documentation/application-notes/AN-352.pdf
    i gess that defines it ? referencing your input to digital ground ? further chk-s . . .
    http://www.analog.com/media/en/technical-documentation/data-sheets/AD790.pdf
    i don't have "data hold" or "latch" working in simulation ... yet
     
    Last edited: Sep 23, 2016
  7. m.serdar

    Thread Starter New Member

    Sep 23, 2016
    3
    0
    I will use it as square wave generator from the output of amplified emg signal...Amplified emg signal peak value is 5 volt and about max. 500Hz...and the referans voltage is 1.7 volt. So if the amplified emg signal is bigger than the referans the output will be 5v..and the other condition it will be zero...I want perfect square so i wonder if i can improve the rising or falling time...
     
  8. ci139

    Member

    Jul 11, 2016
    341
    38
    Google Images [comparator input transformer]
    http://www.ko4bb.com/Timing/ClockShaper.php
    http://electronics.stackexchange.com/questions/47255/sct-sensor-to-0-10v-analog-input
    ((http://www.analog.com/library/analogdialogue/archives/49-04/input_protection.html))
    filter (in the mind) = similar apps , related materials (that might be useful by their context)

    LT1016 - shows the digital ground to be the output ground - either the AD model is not fully integral - or - they define/implement it differently ??? running spice compare ...
    _Draft-AD-comp-E0x.png
     
    Last edited: Sep 23, 2016
  9. ci139

    Member

    Jul 11, 2016
    341
    38
    muhahaa (im so stupid)
    _Draft-AD-comp-E03.png
    i only play computer games such as LT Spice -- i usually dont build/test those things -- !! be aware
     
  10. crutschow

    Expert

    Mar 14, 2008
    13,028
    3,237
    All those decoupling capacitors (why so many? :confused:) have no effect on the simulation since the voltage sources are already ideal (zero ohms impedance).
     
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
     
  12. ci139

    Member

    Jul 11, 2016
    341
    38
    to achieve smoother I(Vx) plot ?
     
  13. crutschow

    Expert

    Mar 14, 2008
    13,028
    3,237
    You could use a thousand capacitors but it would still have no effect on the simulation.
     
  14. ci139

    Member

    Jul 11, 2016
    341
    38
    you seem to be right - but with common detergent it's valid ...
    _Draft-AD-comp-E03a.png
     
  15. crutschow

    Expert

    Mar 14, 2008
    13,028
    3,237
    "common detergent "? :confused:
    Are we doing laundry here?
     
  16. ci139

    Member

    Jul 11, 2016
    341
    38
    Isn't the LT-Spice a washing machine :eek:
     
  17. ronsoy2

    New Member

    Sep 25, 2013
    19
    4
    This could be a measurement problem, not the IC itself. I threw it together and the photo below shows the results. The tremendous overshoot is simply because I used a 6 inch ground lead on the scope clip, it is not really there. But you can see the risetime is well under 10 ns, as the data sheet shows it should be. Are you by chance using a x1 probe? That might load down the output but even that seems like it should give about a hundred nanosecond or so rise. Use a x10 probe and a short as you can get away with ground lead to see the true risetime. testerphoto 001.jpg
     
Loading...