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    RF mixer fails repeatedly..

    Hi,

    I'm wondering what is causing this problem.. can somebody help me..

    I'm doing a (digital + RF) board testing...So there are 3 ports LO-out RF-out & IF-in from the board to connect a mixer board.The RF signal is decided by the digital section it is a 2 carrier W-CDMA signal.The problem is that this mixer board connected to main board fails occasionally..

    I had evaluated this mixer separately and it is working fine...when connecting to the board at certain times this mixer fails & draws more current..

    The LO & RF signal is well within the absolute maximum/typical ratings..
    What could be the problem..??
    Is there any particular sequence to be followed while turning ON the mixer like
    first LO then supply,then RF or something like that??
    The mixer I'm using is HMC483.Can we do something providing some sort of protection in the Mixer PCB??

    Thanks for any help.

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    Re: RF mixer fails repeatedly..

    What about checking for ESD?



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    Re: RF mixer fails repeatedly..

    hmm... How to check for ESD??
    Last edited by themaccabee; 22nd February 2011 at 08:33.



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    Re: RF mixer fails repeatedly..

    Hello,

    With the current info, this can be anything from ESD, transient phenomena during power up/power down, use outside typical operating conditions, etc.


    Just some things:
    -If the mixer functions, are voltages, currents, etc as expected?
    -Does the mixer fail during operation (with the main board), or immediately after cycling power or other repeatable issue?
    -Do they also fail when running in the lab (under controlled environment, free from ESD isssues)?
    -Do coupling capacitors towards the ports have correct value (and is this value really present on the circuit boards)?
    -Are all supplies stable (so do they supply correct voltage/current and aren't oscillating)?


    1 members found this post helpful.

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    Re: RF mixer fails repeatedly..

    Thank you WimRFP for the suggestions.
    I was thinking on what you said as the second & fourth points.

    Last time i remember the mixer failed , is when i had given RF & LO ,also the IF port was connected to the board .Then when i powered the mixer with the right voltage it was gone.( it drew more current from the supply & current limit LED turned ON)

    So is there any problem that only after the Power supply has been steady RF & LO should be applied or something like that.???
    Any suggestions are most welcome
    Thanks



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    Re: RF mixer fails repeatedly..

    Hello,

    Assuming that RF and LO levels are well within maximum ratings, I don't believe that powering with RF and LO present, and IF connected is a problem.

    Are you sure you didn't damage the mixer by charging discharging a too large DC blocking capacitor in the LO, RF or IF circuitry? Can there be a problem in the sequence that connections are made (for example signal wire makes before corresponding return)? This may lead to ESD like problems.



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    Re: RF mixer fails repeatedly..

    I would guess it is one of 2 things:

    1) power supply sequencing. Some RF circuits draw too much current if the positive voltage is applied before the negative voltage. You may have that sort of problem going on. You might need a sequencer circuit that turns off the positive supply voltage unless the negative voltage is there.l

    2) Something is oscillating as it turns on. YOu might have a FET that is capable of oscilating at higher power (>1 watt). Normally, it has a small signal output, but under some condition (like the RF signal not yet present) it can oscillate at a very high power. This high power oscillation blows up the mixer.



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    Re: RF mixer fails repeatedly..

    Thank you guys for the suggestions,
    1) power supply sequencing. Some RF circuits draw too much current if the positive voltage is applied before the negative voltage. You may have that sort of problem going on. You might need a sequencer circuit that turns off the positive supply voltage unless the negative voltage is there.l
    I power the mixer board (5V,GND)from a bench top PSU.I always connect the GND wire before connecting the +5V wire.I hope its ok.

    The test setup i had been using is as follows,

    Are you sure you didn't damage the mixer by charging discharging a too large DC blocking capacitor in the LO, RF or IF circuitry?
    I ve used the capacitor Values as described in the picture..i m not sure about the design can someone tell me whether it is ok?
    What the datasheet says about IF pin is
    This pin is DC coupled. For applications not requiring
    operation to DC this port should be DC blocked externally
    sing a series capacitor. Choose value of capacitor to pass
    IF frequency desired. For operation to DC, this pin must
    not sink/source more than 40 mA of current or failure may
    result.



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    Re: RF mixer fails repeatedly..

    If you only have one single supply at +5v, you can not have a sequencing problem! I meant if you had both +5 and -5V supplies.



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