DIY Ghz sampling head for <100Mhz scopes

[jcbottorff]

How about the MMDL301T1G as a sampling diode? The datasheet says the typical capacitance is 0.9 pF, the minority carrier lifetime is typically 15 ps, and a reverse leakage of typically 13 nADC. They're also $10 for 100 on Digikey (or $0.25/each), with 150K shown as available anywhere on Octopart.

The Avago quad bridge diodes, HSMS-282P-TR1G seems to be going fast on Digikey, there were about 3K a few days ago and I just bough 20 (as I've been toying with sampler ideas), with less than 500 left. Mouser still has about 800. The plus of the multi-device package is the diodes are claimed to be better matched, which is good for a sampling bridge.

Jan

[David Hess]

How about the MMDL301T1G as a sampling diode? The datasheet says the typical capacitance is 0.9 pF, the minority carrier lifetime is typically 15 ps, and a reverse leakage of typically 13 nADC. They're also $10 for 100 on Digikey (or $0.25/each), with 150K shown as available anywhere on Octopart.

Try them and find out.  They are a higher voltage part with higher capacitance though.

The Avago quad bridge diodes, HSMS-282P-TR1G seems to be going fast on Digikey, there were about 3K a few days ago and I just bough 20 (as I've been toying with sampler ideas), with less than 500 left. Mouser still has about 800. The plus of the multi-device package is the diodes are claimed to be better matched, which is good for a sampling bridge.

I think dual diodes make for a better layout and not all samplers use a four diode bridge.  In addition, using two schottky diodes in series for each element seems to yield much better results.

[Marco]

Why not build a sampling gate from a single diode? With the double diode setup ala LLNL the diode voltage theoretically cancels out, but you have to calibrate these things digitally any. Every extra component makes things slower with discretes. Tek could afford long ago to put tiny raw dies on subtrates and modern MMICs can use introductory electronics course component modeling into 10s of GHz ... but not us lesser souls. Of course others must have followed the same reasoning, so with my Google skills I found this patent.

UHS logic could provide a fast step with reasonable amplitude. Or if you want something even faster, the reverse recovery of a saturated BJT.