Good Rectifier Diode for High Frequecies?

Discussion in 'General Electronics Chat' started by dumindu89, Jul 3, 2012.

  1. dumindu89

    Thread Starter Member

    Oct 28, 2010
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    I am searching for a good rectifier diode for high frequencies such as 125 MHz to use as a half wave rectifier. If you know such a one please let me know the part number.

    Thanks.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  3. Sensacell

    Well-Known Member

    Jun 19, 2012
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    A PIN diode is a good RF switch, but not a good rectifier. At those frequencies, there may be another way to do it that doesn't involve diode reverse recovery time, which is still about 4 ns in a really fast PN diode. Perhaps a Schottky diode, those beasts can switch in picoseconds, so I hear.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    A Schottky diode would likely work best at those frequencies since it has a very fast reverse recovery. Is this for signal detection (low current)?
     
  5. dumindu89

    Thread Starter Member

    Oct 28, 2010
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    I just need to remove the negative pulse of a sinusoidal wave form. The output will be an input to an IC of 74F series and I need to protect the IC from negative pulses going through the IC.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Then a Schottky would be best. Any Schottky with a voltage rating of 20V or more and a 100mA or more current rating (such as a MBR0520L) should work. Note that you need a series resistor in front of the diode to limit the current.
     
  7. dumindu89

    Thread Starter Member

    Oct 28, 2010
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    I simulated the MBR0520L diode using NI Multisim to check whether it is working in 100 MHz. But it is still giving a the full sinusoidal wave with no half wave rectification at 100 MHz as the output while it is rectifying around 100 kHz. :(

    Will the 74F IC damaged if I do not use a rectifier diode (Maximum output voltage of this sinusoidal wave is 5V) ?
     
    Last edited: Jul 3, 2012
  8. crutschow

    Expert

    Mar 14, 2008
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    You should be able to use the input protection diode on the 74F circuit to limit the negative voltage. Per the 74F data sheet Absolute Maximum Ratings, you must add a series resistor to limit the input current to -30mA (that would be >170Ω for 5V).
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    A germanium diode like 1N34A is very fast but only at very low current.

    Shcottky's are second fastest, silicon type are slowest. Since you didn't spec current, it's hard to pick a component.
     
  10. dumindu89

    Thread Starter Member

    Oct 28, 2010
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    I used a resistor and limited the current and sent the sinusoidal input to the 74F TTL IC and got a output as follows. But the expected output should be a pure square wave.
    [​IMG]

    I think the TTL IC cannot determine what would be the output for the voltages between the Low-level input voltage (0.8V) to High-level input voltage (2V).

    Any effective way to convert this sinusoidal signal to a discrete signal (around 100 MHz) before I input it to a 74F TTL IC?
     
  11. crutschow

    Expert

    Mar 14, 2008
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    Your scope does not show a stable signal so I can't see what is happening. Is the actual signal unstable?

    If so, there are two possible ways to improve it.

    One is to increase the value of the AC voltage so that the input 74F protection diodes act like a clamp on both the positive and negative transitions to square up the input signal.

    The other is to use a 74F Schmidt trigger (if they make one) to avoid any oscillations at the input voltage switch point.
     
  12. takao21203

    Distinguished Member

    Apr 28, 2012
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    I would try a glass 1n4148.

    They are good rectifiers for small switchers.
     
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