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Sampler diodes with more barrier height?

Started by Joerg February 15, 2014
John Larkin wrote:
> On Thu, 27 Feb 2014 17:56:05 -0800, Joerg <invalid@invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Thu, 27 Feb 2014 17:59:16 +0100, Gerhard Hoffmann <dk4xp@arcor.de> wrote: >>> >>>> Am 27.02.2014 16:02, schrieb John Larkin: >>>>> Several people still make SRDs. M-pulse, Metelics, MAcom (all SRD makers start >>>>> with "M") >>>>> >>>>> MA44767 and MA44769 are SOT23 distributor items, 50-75 cents range. >>>>> >>>> Ah, found them under varactors @Mouser, at least the MA144769-287T >>>> But 600 ps transition time is not that wonderful anymore, got >>>> half a ns from Fairchild NC7sz04p5x :-) >>>> Nobody escapes the CMOS steamroller! >>>> >>>> thanks, Gerhard >>> The 44769 is rated 150 ps transition time, but they will go a bit faster if you >>> drive them hard. >>> >>> The fastest catalog items are around 25-30 ps. >>> >>> http://www.aeroflex.com/AMS/Metelics/micro-metelics-prods-SRDs-beamlead.cfm >>> >>> Somebody makes some really fast 0402 sized parts, can't remember who. >>> >>> Fast SRDs don't store much charge, so they are hard to drive. >>> >> <100psec should be doable with a BFP740 and similar ones with the base >> driven sledgehammer-style. Of course, only very few volts allowed at the >> collector. > > Have you tried that? My experiments along those lines have been > disappointing. >
Not with the BFP yet but with a BFR92 and it performed quite nicely. What happened in your case? How did you drive them?
> PHEMTS switch screamingly fast, and the gates are relatively easy to > drive. Good SRD drivers. In the old tek samplers, they usually used an > avalanche transistor to drive the SRD. HP tended to use a transistor > driving a slow srd driving a fast srd. >
I want to keep things simple. PHEMTs are nice but need a lot of fast gate swing unless followed by an SRD. BJTs almost snap from zero to saturation withing about 100mV on the drive ramp. I don't really care about saturation and recovery because the PRF is low. BJTs are often used for cheap transmitters at UHF or above. Example: http://www.nxp.com/documents/data_sheet/BFG480W.pdf Compression is at +20dBm at 2GHz which is pretty much full swing. Some of the MMIC should also be able to do this but unfortunately have a different pinout. Northrop-Grumman makes massive (and probably very expensive) BJT if you need tons of pulse energy for pulsed radar: http://www.northropgrumman.com/Capabilities/BipolarRFTransistors/Documents/WPTB48F2729Cx.pdf?pdf=Datasheet -- Regards, Joerg http://www.analogconsultants.com/