mwmmboy said:Hi, what is the operating frequency? Are you sure that with a so hogh power there are not some radianting effects? Is the layout carefully designed?
Bye
vfone said:MA4P7104 is not working properly for frequencies higher than 500MHz.
biff44 said:Did you have it biased up properly? 100 mA per diode when forward biased and 100 VDC reverse bias?
Also, you might have blown out the diodes when switching from one state to the other. Most people turn off the RF high power when switching, and turn the RF back on well after they are sure the diodes have switched. Notice that the thermal resistance is very high for a "high power" diode, meaning they are NOT designed for actually dissipating a lot of heat. Silicon diodes really should not be running over 150 degrees C for even short periods, and 120 degrees C in the steady state. That means that the diodes junction to lead temperature, and lead to ground plane temperature, can not add up to very much!
biff44 said:Well, its been a while. let me see what I can remember!
I am assuming you have a two throw switch here (SPDT, one input and two selectable outputs).
So lets say one of the diodes is forward biased at 80 mA. We will call this D1.
.........
Good luck.
biff44 said:One other thing to check is self rectification. The diode is big enough (thick I region) so that it should not be doing, but it would be worthwhile to check that that is true. When the high power is applied, does the 80 mA forward bias change, as read on a digital current meter?
biff44 said:Interesting point. I did not see those graphs. The data sheet does have some graphs that show parallel resistance diving quickly up to 600 MHz. If those sheets can be extrapolated, then the parallel resistance is more like 2K ohm at 900 MHz (not the 10K I assumed), so power dissipation in reverse biase may be more like 44.7²/2 Kohm = 1 watt. Add some VSWR, etc, and maybe the diode is just overheating, breaking down, and then failing.
And the data sheet shows no series resistance data other than 100 MHz, so what if it changes a lot at 900 MHz also?
biff44 said:2.5 dB of loss for a high power switch is too high. 16 branches? Resistor bias? You are saying things that do not make much sense. post a schematic.
biff44 said:Paste your schemtic into something like MS word, and upload it while posting.
Putting Pin diodes into a filter negates everything posted on this thread so far. Please try not to waste people's time next time.
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