ChesterW and I have spent the last couple of days doing a dead-bug proto of a single-diode TDR front end I designed for a mutual client. It uses all SOT23, SC-70, 0603, and a super small (0402ish) sampling diode. It includes the TX pulse generator, sample pulse generator, sampling diode, and a ~100~MHz bandwidth buffer and voltage amplifier
Connectors are MMCX to minimize pigtail inductance. Nice clean sampling response, 150-ps 10%-90% (probably 100 ps FWHM), 17 ps p-p jitter, BOM cost $1.30 excluding connectors. (I cheated slightly by replacing the BJT pulse generators with pHEMTs--an extra 80 cents--to make up for the higher stray inductances, so it's really $2.10.)
Chester's bit is the delay generator, back end, and all the secret sauce in the actual transducer we're measuring. It's all done, so he came up from Dallas to lend a shoulder to the prototyping wheel, which was great.
For the test, we used one of JL's very nice P400 digital delay generators to do the timing. That 17 ps jitter number is pretty good, I think, especially since there's no shielding and a bunch of cell phones around. It's neat to be able to tune the delay by 10 ps and see the sampler output change.
Prototyping is sure slow when you're fighting the surface tension of the solder and the tendency of all of the midair solder joints to melt at once. 0603-pitch pad board with ground plane is a big win for this sort of job, but some of the hairiest mid-air things took 10 tries to get right, even under a Mantis.
Fun doing my first-ever sampler, though!
Cheers
Phil Hobbs