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    tx rx switch

    Hi,
    Could someone suggest PIN diodes for a Tx/Rx switch for a transceiver with 4W output power. Frequency 300Mhz up to 800Mhz.

    •   Alt6th April 2009, 10:35

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    m/a-com|pin diode




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    pin diode rx tx

    Hi,
    Is it the forward current that is the limiting factor for the diode to be usable at certain power?
    and another question, Do I need a negative bias voltage if I make the switch with HSMP3832, which is two diodes in series and using the circuit in fig.9 from the datasheet.
    Thanks



    •   Alt6th April 2009, 13:07

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    how to make a diode switch

    I think you will find that that avago pin diode will blow up if you try to use it with 4 watts.

    What isolation do you need in the unselected arm? Do you care about intermods generated in the switch? What is your max insertion loss? Do you care if it takes a long time to switch, say 200 uS?

    It will work better with both positive and negative supplies. Do you mind if the diodes have to be wirebonded?

    Rich
    Last edited by keith1200rs; 1st May 2012 at 09:54. Reason: Advertising removed



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    switch rx tx

    Hi,
    Thanks for the reply.
    I will use it in a handheld radio operating in 300MHz-470MHz, FSK transmision.
    I don't care about distortions, isolation (to some extend, I have to remember that I have a receiver connected to antenna , when the TX is transmitting with 4W, I hope the switch will isolate it).
    I don't care about switching times etc.....
    I would prefer not to use negative voltages, at the moment I have +12 and +3.3V and I would prefer not to add any new voltage converters.

    What diodes do you suggest?
    What parameters are important at this power?



  6. #6
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    4 pin diodes

    And you do not want to use a FET switch for what reason?

    http://www.hittite.com/products/view...view/HMC574MS8

    A pin diode switch will, at the least, have two series diodes at a junction, and more likely have a pair of series-shunt PIN diodes to get the isolation you want to have to protect the receiver. In a series shunt configuration, when the transmitter arm is on, the series diode is strongly forward biased (say 30 mA current), and the shunt diode is reverse biased. For 4 watts, you might want to put -10 volts across that reverse biased diode. This keeps it from partially turning on, which would increase the insertion loss, and in a worst case make the diode fail due to heat.

    If you do not have the -10 Volts, then you have to pick a diode that has a very thick "I" region, so that the diode can not forward bias itself with the 4 watt signal. there are some other issues to consider, related to your pretty low operating frequency (Punch Through).

    So if you really want a 4 W PIN switch, you have to carefully research the diode
    itself.


    Rich

    Added after 10 minutes:

    Something like this type of diode would work well:
    http://www.mpdigest.com/issue/Articl...MA/Default.asp
    Last edited by keith1200rs; 1st May 2012 at 09:54. Reason: Advertising removed



  7. #7
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    masw-000825-12770t

    I notice that M/a-com has a new 20 W pin diode swtich ic, the MASW-000825-12770T, plastic packaged.



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