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Sampler diodes with more barrier height?

Started by Joerg February 15, 2014
Joerg wrote:
> Folks, > > After John Larkin sent me SMS7621 Schottky RF diodes I played around > with them in the lab. While they perform nicely at room temperature > everything goes to pots at a slightly elevated temperature. At ballpark > 50C the leakage current is already painfully high for use as a sampler > diode. > > Question: Is there a fast RF diode or sampling diode in a reasonable > cost range (low single-digit Dollars) with more barrier height? In > samplers one doesn't care so much about Vf but unfortunately many such > diodes are marketed as RF detectors where Vf does matter. I guess that's > why they leak so much when the temps go up. >
Schottky, like Germanium diodes are inherently leaky (very similar that way) because of the low Vf. A standard plain silicon diode is far better and has a higher barrier height; thousands to choose from, and a fair number of fast ones at decent prices.
On Sat, 15 Feb 2014 17:01:36 -0800, Joerg <invalid@invalid.invalid> wrote:

>John Larkin wrote: >> On Sat, 15 Feb 2014 13:54:05 -0800, Joerg <invalid@invalid.invalid> wrote: >> >>> Folks, >>> >>> After John Larkin sent me SMS7621 Schottky RF diodes I played around >>> with them in the lab. While they perform nicely at room temperature >>> everything goes to pots at a slightly elevated temperature. At ballpark >>> 50C the leakage current is already painfully high for use as a sampler >>> diode. >>> >>> Question: Is there a fast RF diode or sampling diode in a reasonable >>> cost range (low single-digit Dollars) with more barrier height? In >>> samplers one doesn't care so much about Vf but unfortunately many such >>> diodes are marketed as RF detectors where Vf does matter. I guess that's >>> why they leak so much when the temps go up. >> >> The classic 2-diode feedback sampler doesn't much care about leakage. Within >> about a microsecond after the sampling pulse, the delta-v glitch is amplified in >> a charge amp, usually back up to 100% sampling efficiency, and dumped into a >> slow s/h. That voltage, with the diode back-biases, is applied back onto the >> diodes for the next shot. That makes the overall sampling process ultra-linear >> and allows it to work down to very low trigger rates. >> > >If push comes to shove I'll have to use a 2-diode sampler and figure out >a balun for driving. I could also use a follow-up S&H on my single-diode >sampler but it's a real estate and cost issue. Essentially my range gate >will be around 300psec and the sampling cannot happen more than about >once per usec. So around 3000:1. Delta-V is a few tens to hundreds of uV. > > >> There are higher-barrier diodes in the Skyworks family. They have a great sample >> kit. >> > >I think I'll have to talk to the guys there. Things like Schottky >barrier height aren't in the datasheets but their FAEs should know. > > >> What sort of risetime did you get? Are you doing an open-loop sampler? What the >> sampling pulse generator like? >> > >I haven't tried the diodes in a sampler yet because the sampler only >exists on paper so far. > >The sim shows about 120psec rise time. Open loop sampler. Essentially an >RF BJT driven hard by a fast logic chip and then the collector signal is >capacitively coupled into the sampler (fractions of a pF). > >One of the challenges with a post-S&H is that there seem to be no ICs >for that. The SMP04 still needs 4usec, too long, and it costs an arm and >a leg. It's a pity they don't sell the fast samplers from ADCs sans the >ADC. "I'd like to have burger and fries but without the burger".
I did it with discretes; a low charge injection analog switch would work in the downstream s/h. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
On Sun, 16 Feb 2014 02:53:57 +0100, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

>Am 16.02.2014 02:40, schrieb Joerg: >> Gerhard Hoffmann wrote: >>> Am 15.02.2014 22:54, schrieb Joerg: > >> I'll call Skyworks and see what else they can offer. Maybe something >> that isn't so mainstream at distributros but longterm available. >> >> >>> ... Abuse a MGF1302 gate that you may have in your junk box? >>> >> >> It needs to be something that's not unobtanium :-) > >MGF1302 & friends have been workhorses for ham EME for decades... >Someone still makes GaAsFETs, no???? > >:-) Gerhard >
Data sheet: <http://oh3tr.ele.tut.fi/~ftp/atv/mgf1302.pdf> "Where to find MGF-1302's" <http://www.dxmaps.com/mgf1302.html> ...and of course, there's eBay: <www.ebay.com/sch/i.html?_nkw=mgf1302> I use one in an antenna mounted preamp for my 1090 MHz ADS-B receiver. About 0.5dB NF and 20dB gain. Kinda overkill using a 4-8GHz GaAsFET at 1GHz, but they were cheap and easy to ummm... "borrow". -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
"Robert Baer" <robertbaer@localnet.com> wrote in message 
news:DnVLu.407695$PK.221670@fx23.iad...
> Schottky, like Germanium diodes are inherently leaky (very similar > that way) because of the low Vf. > A standard plain silicon diode is far better and has a higher barrier > height; thousands to choose from, and a fair number of fast ones at > decent prices.
A mere 1N4148 for instance is already in the same ballpark as others (i.e., 1-2pF CJO, or something like that), while being a massively better conductor (Vf ~ 0.7V up to, what, a few 100mA, as compared to that BAR18 I mentioned which goes resistive in the 10s of mA). But do PN junction diodes exist with short enough forward and reverse recovery times to actually handle a 200ps pulse? Could one made of GaAs or whatever be better? ...Could a very small LED be suitable? Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
On 2/15/2014 8:01 PM, Joerg wrote:
> John Larkin wrote: >> On Sat, 15 Feb 2014 13:54:05 -0800, Joerg <invalid@invalid.invalid> wrote: >> >>> Folks, >>> >>> After John Larkin sent me SMS7621 Schottky RF diodes I played around >>> with them in the lab. While they perform nicely at room temperature >>> everything goes to pots at a slightly elevated temperature. At ballpark >>> 50C the leakage current is already painfully high for use as a sampler >>> diode. >>> >>> Question: Is there a fast RF diode or sampling diode in a reasonable >>> cost range (low single-digit Dollars) with more barrier height? In >>> samplers one doesn't care so much about Vf but unfortunately many such >>> diodes are marketed as RF detectors where Vf does matter. I guess that's >>> why they leak so much when the temps go up. >> >> The classic 2-diode feedback sampler doesn't much care about leakage. Within >> about a microsecond after the sampling pulse, the delta-v glitch is amplified in >> a charge amp, usually back up to 100% sampling efficiency, and dumped into a >> slow s/h. That voltage, with the diode back-biases, is applied back onto the >> diodes for the next shot. That makes the overall sampling process ultra-linear >> and allows it to work down to very low trigger rates. >> > > If push comes to shove I'll have to use a 2-diode sampler and figure out > a balun for driving. I could also use a follow-up S&H on my single-diode > sampler but it's a real estate and cost issue. Essentially my range gate > will be around 300psec and the sampling cannot happen more than about > once per usec. So around 3000:1. Delta-V is a few tens to hundreds of uV. > > >> There are higher-barrier diodes in the Skyworks family. They have a great sample >> kit. >> > > I think I'll have to talk to the guys there. Things like Schottky > barrier height aren't in the datasheets but their FAEs should know. > > >> What sort of risetime did you get? Are you doing an open-loop sampler? What the >> sampling pulse generator like? >> > > I haven't tried the diodes in a sampler yet because the sampler only > exists on paper so far. > > The sim shows about 120psec rise time. Open loop sampler. Essentially an > RF BJT driven hard by a fast logic chip and then the collector signal is > capacitively coupled into the sampler (fractions of a pF). > > One of the challenges with a post-S&H is that there seem to be no ICs > for that. The SMP04 still needs 4usec, too long, and it costs an arm and > a leg. It's a pity they don't sell the fast samplers from ADCs sans the > ADC. "I'd like to have burger and fries but without the burger". >
There are lots of nice analogue muxes with very low charge injection, and the dual-gate MOSFET trick works even better. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On 2/16/2014 8:43 AM, Tim Williams wrote:
> "Robert Baer" <robertbaer@localnet.com> wrote in message > news:DnVLu.407695$PK.221670@fx23.iad... >> Schottky, like Germanium diodes are inherently leaky (very similar >> that way) because of the low Vf. >> A standard plain silicon diode is far better and has a higher barrier >> height; thousands to choose from, and a fair number of fast ones at >> decent prices. > > A mere 1N4148 for instance is already in the same ballpark as others > (i.e., 1-2pF CJO, or something like that), while being a massively better > conductor (Vf ~ 0.7V up to, what, a few 100mA, as compared to that BAR18 I > mentioned which goes resistive in the 10s of mA). But do PN junction > diodes exist with short enough forward and reverse recovery times to > actually handle a 200ps pulse? Could one made of GaAs or whatever be > better? ...Could a very small LED be suitable? > > Tim >
Pretty well has to be Schottky, because PN junctions of whatever sort have diffusion delays that slow things down very badly. You can't do picosecond sampling with a 1N4148 because it doesn't turn on fast enough. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
In article <ldqf8e$f89$1@dont-email.me>, tmoranwms@charter.net says...
> > "Robert Baer" <robertbaer@localnet.com> wrote in message > news:DnVLu.407695$PK.221670@fx23.iad... > > Schottky, like Germanium diodes are inherently leaky (very similar > > that way) because of the low Vf. > > A standard plain silicon diode is far better and has a higher barrier > > height; thousands to choose from, and a fair number of fast ones at > > decent prices. > > A mere 1N4148 for instance is already in the same ballpark as others > (i.e., 1-2pF CJO, or something like that), while being a massively better > conductor (Vf ~ 0.7V up to, what, a few 100mA, as compared to that BAR18 I > mentioned which goes resistive in the 10s of mA). But do PN junction > diodes exist with short enough forward and reverse recovery times to > actually handle a 200ps pulse? Could one made of GaAs or whatever be > better? ...Could a very small LED be suitable? > > Tim
Too bad the terahertz detector methods couldn't be utilized downward abit. There seems to be more available with detecting that spectrum. Devices like the Golay cell, bolometer, pyroelectric effect, the photo rectification (acoustic which I don't think would work any how).. As for pulsing lasers onto a semi for a detector, I would think the semi would need to be of a large area for the Ghz, if it would work at all? Jamie etc..
"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message 
news:RJ-dncV0roJiUJ3OnZ2dnUVZ_oKdnZ2d@supernews.com...
> Pretty well has to be Schottky, because PN junctions of whatever sort > have diffusion delays that slow things down very badly. > > You can't do picosecond sampling with a 1N4148 because it doesn't turn > on fast enough.
Yeah, that's the point pretty much. I already know a 1N4148 takes a nanosecond or so to do anything, besides blowing the CJO spec by about 5x. But I don't know if there's anything with faster diffusion (GaAs?) or thinner junctions that could do better. Only other thing that comes to mind, then, would be a really small thermionic diode, which doesn't depend on diffusion, more or less (transport is ballistic). The best I have is a few of these, http://www.mif.pg.gda.pl/homepages/frank/sheets/140/2/2-01C.pdf but they're physically much too large for sort of application (self resonant frequency 2.8GHz, plus the feed-throughs for the 5V 0.3A heater, each). But really, even the engineers from the '40s knew the limits of their technology, and though there may be some planar diodes (with flange or coax terminals for mounting in waveguides or cavities), early "hot carrier" (schottky) diodes, e.g., cartridge style, were pretty much the way to go. And hey, there's some on eBay right now: http://www.ebay.com/itm/4-PCS-SYLVANIA-1N23B-S-X-BAND-MICROWAVE-DIODES-TESTED-DET-MIXER-RADAR-/281155049826 Geez, I can't even find specs on the things. Datasheets yes, but they're entirely about VSWR and noise figure -- not even about bias, let alone capacitance! Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
On Sat, 15 Feb 2014 17:01:36 -0800, Joerg <invalid@invalid.invalid> wrote:

>John Larkin wrote: >> On Sat, 15 Feb 2014 13:54:05 -0800, Joerg <invalid@invalid.invalid> wrote: >> >>> Folks, >>> >>> After John Larkin sent me SMS7621 Schottky RF diodes I played around >>> with them in the lab. While they perform nicely at room temperature >>> everything goes to pots at a slightly elevated temperature. At ballpark >>> 50C the leakage current is already painfully high for use as a sampler >>> diode. >>> >>> Question: Is there a fast RF diode or sampling diode in a reasonable >>> cost range (low single-digit Dollars) with more barrier height? In >>> samplers one doesn't care so much about Vf but unfortunately many such >>> diodes are marketed as RF detectors where Vf does matter. I guess that's >>> why they leak so much when the temps go up. >> >> The classic 2-diode feedback sampler doesn't much care about leakage. Within >> about a microsecond after the sampling pulse, the delta-v glitch is amplified in >> a charge amp, usually back up to 100% sampling efficiency, and dumped into a >> slow s/h. That voltage, with the diode back-biases, is applied back onto the >> diodes for the next shot. That makes the overall sampling process ultra-linear >> and allows it to work down to very low trigger rates. >> > >If push comes to shove I'll have to use a 2-diode sampler and figure out >a balun for driving. I could also use a follow-up S&H on my single-diode >sampler but it's a real estate and cost issue. Essentially my range gate >will be around 300psec and the sampling cannot happen more than about >once per usec. So around 3000:1. Delta-V is a few tens to hundreds of uV. > > >> There are higher-barrier diodes in the Skyworks family. They have a great sample >> kit. >> > >I think I'll have to talk to the guys there. Things like Schottky >barrier height aren't in the datasheets but their FAEs should know. > > >> What sort of risetime did you get? Are you doing an open-loop sampler? What the >> sampling pulse generator like? >> > >I haven't tried the diodes in a sampler yet because the sampler only >exists on paper so far. > >The sim shows about 120psec rise time. Open loop sampler. Essentially an >RF BJT driven hard by a fast logic chip and then the collector signal is >capacitively coupled into the sampler (fractions of a pF).
Be wary of the BJT response. I've pulsed all sorts of BJTs, including some of the 45 GHz SiGe parts, and have never seen especially fast output edges. Phemts are different; they can switch fast. Sampling pulses are usually created with SRDs and clipping lines. The really fast samplers use NLTL shock lines. SRD steps are usually pretty-fast steps that are made faster and cleaner with steering diodes. See Agoston's patents. People worked very hard to build samplers and step generators that had clean picosecond response. I've done a little playing with software deconvolution for TDR. The idea is to build a fast but ugly sampling or TDR system and clean up its step response with a software FIR filter, the problem being how to train the filter. https://dl.dropboxusercontent.com/u/53724080/Sampling/TDR_Decon_demo.jpg I have an algorithm that seems to work well, although I've never really understood it. It just seemed like a reasonable thing to do. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
On 2/15/2014 9:28 PM, Robert Baer wrote:
> Joerg wrote: >> Folks, >> >> After John Larkin sent me SMS7621 Schottky RF diodes I played around >> with them in the lab. While they perform nicely at room temperature >> everything goes to pots at a slightly elevated temperature. At ballpark >> 50C the leakage current is already painfully high for use as a sampler >> diode. >> >> Question: Is there a fast RF diode or sampling diode in a reasonable >> cost range (low single-digit Dollars) with more barrier height? In >> samplers one doesn't care so much about Vf but unfortunately many such >> diodes are marketed as RF detectors where Vf does matter. I guess that's >> why they leak so much when the temps go up. >> > Schottky, like Germanium diodes are inherently leaky (very similar > that way) because of the low Vf. > A standard plain silicon diode is far better and has a higher barrier > height; thousands to choose from, and a fair number of fast ones at > decent prices. >
Not at picosecond speeds, there aren't. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net