Sample and Hold Circuit Help!!

Discussion in 'General Electronics Chat' started by syee10, Oct 11, 2010.

  1. syee10

    Thread Starter Member

    Mar 26, 2010
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    Hi all,

    I am designing a simple sample and hold circuit where the input is a sinusoidal analog input and it is control by a TTL compatible square wave (waveform A). The result waveform i should get is waveform B in the attach file but i tried a millions time i still cant get the same waveform. Someone there can help me out? I had attached all the file in the attachment..
     
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  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I can make a sample and hold (track and hold, more accurately) using your circuit, with a couple of mods. On mine, though, when the sample pulse goes high, the output follows the input instead of being clipped at ground like your output waveform.
     
  3. syee10

    Thread Starter Member

    Mar 26, 2010
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    0
    Can you get the same result as the waveform in 'B' using the circuit i constructed?
     
  4. joemmech

    Member

    Jan 22, 2010
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    0
    If you want a sample and hold circuit, you can try using the HA-5320 IC. It is a sample and hold circuit IC. I have already used it and it is working...Below is the link to its datasheet:

    http://www.intersil.com/data/fn/fn2857.pdf
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Below is my circuit and the results. I have included the .ASC file so that it can be simulated in LTspice.
    I used a different op amp because I did not have a model of LF412.
     
  6. syee10

    Thread Starter Member

    Mar 26, 2010
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    0
    Ron..

    Your result is exactly what i want..anyway i cant open the file you attached here..can you send me the LF356.sub? Thank you =)
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Copy and paste this into Notepad, and save it as ...\lib\sub\LF356.sub.
    Code ( (Unknown Language)):
    1. * connections:    non-inverting input
    2. *                 |   inverting input
    3. *                 |   |   positive power supply
    4. *                 |   |   |   negative power supply
    5. *                 |   |   |   |   output
    6. *                 |   |   |   |   |
    7. *                 |   |   |   |   |
    8. .SUBCKT LF356     1   2  99  50  28
    9. *
    10. *Features:
    11. *Low input bias current =             30pA
    12. *Low input offset current =            3pA
    13. *High input impedance =              1Tohm
    14. *Low input offset voltage =            1mV
    15. *
    16. ****************INPUT STAGE**************
    17. *
    18. IOS 2 1 3P
    19. *^Input offset current
    20. R1 1 3 1E12
    21. R2 3 2 1E12
    22. I1 99 4 100U
    23. J1 5 2 4 JX
    24. J2 6 7 4 JX
    25. R3 5 50 20K
    26. R4 6 50 20K
    27. *Fp2=20 MHz
    28. C4 5 6 1.9894E-13
    29. *
    30. ***********COMMON MODE EFFECT***********
    31. *
    32. I2 99 50 4.65MA
    33. *^Quiescent supply current
    34. EOS 7 1 POLY(1) 16 49 3E-3 1
    35. *Input offset voltage.^
    36. R8 99 49 50K
    37. R9 49 50 50K
    38. *
    39. *********OUTPUT VOLTAGE LIMITING********
    40. V2 99 8 2.63
    41. D1 9 8 DX
    42. D2 10 9 DX
    43. V3 10 50 2.63
    44. *
    45. **************SECOND STAGE**************
    46. *
    47. EH 99 98 99 49 1
    48. F1 9 98 POLY(1) VA3 0 0 0 1.5944E7
    49. G1 98 9 5 6 2E-3
    50. R5 98 9 100MEG
    51. VA3 9 11 0
    52. *Fp1=31.96 HZ
    53. C3 98 11 49.9798P
    54. *
    55. *********COMMON-MODE ZERO STAGE*********
    56. *
    57. G4 98 16 3 49 1E-8
    58. L2 98 17 530.52M
    59. R13 17 16 1K
    60. *
    61. **************OUTPUT STAGE**************
    62. *
    63. F6  99 50 VA7 1
    64. F5  99 23 VA8 1
    65. D5  21 23 DX
    66. VA7 99 21 0
    67. D6  23 99 DX
    68. E1  99 26 99 9 1
    69. VA8 26 27 0
    70. R16 27 28 20
    71. V5  28 25 -.25V
    72. D4  25  9 DX
    73. V4  24 28 -.25V
    74. D3   9 24 DX
    75. *
    76. ***************MODELS USED**************
    77. *
    78. .MODEL DX D(IS=1E-15)
    79. .MODEL JX PJF(BETA=1.25E-5 VTO=-2.00 IS=30E-12)
    80. *
    81. .ENDS
     
  8. syee10

    Thread Starter Member

    Mar 26, 2010
    59
    0
    Ron..

    Thanks ron..actually i am using Labcenter Proteus to do my simulation..but i already tried to use LTspice and it works.. but i wonder what parameter you change to get the sample waveform? I only can get the hold waveform with my Proteus.. so i need to know which parameter i can change to get sample waveform.. the switch is not the active device rite?
     
  9. syee10

    Thread Starter Member

    Mar 26, 2010
    59
    0
    Thanks for your help =)
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I'm not familiar with Proteus. Maybe one of the other members can help.
     
  11. syee10

    Thread Starter Member

    Mar 26, 2010
    59
    0
    Ron,

    Now i have a similar question about it. What if i change the input voltage source to a input current source?the result waveform i want to get is exactly the same with the previous input voltage source. I tried to replace the input voltage source already but i still cannot get the correct output sample and hold waveform. The output waveform of the current i get is continuous zero value. So do you have any idea? Please reply me asap if possible. Thank you
     
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  12. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Why do you want to use current as an input? Where is the current coming from?
    Current will not flow into an open circuit (the input of U1). Remember Ohms law: V=I*R. If R is infinite, V will be infinite.
     
  13. ifixit

    Distinguished Member

    Nov 20, 2008
    638
    108
    Your sample and hold circuit needs a voltage input to work. To convert a current source back to a voltage, put a resistor of a suitable value from the U1 + input to ground.

    Regards,
    Ifixit
     
  14. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Or dump it into the inverting input of a feedback amplifier.
     
  15. syee10

    Thread Starter Member

    Mar 26, 2010
    59
    0
    Based on the journal, there's 2 sample/hold circuit. One for input voltage signal and another one for input current signal? So i need to construct a sample/hold circuit with current input...
     
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