On Wed, 20 Oct 2021 22:24:36 +0200, Jeroen Belleman <jeroen@nospam.please> wrote:>On 2021-10-20 20:11, Dimiter_Popoff wrote: >> On 10/20/2021 21:04, Jeroen Belleman wrote: >>> On 2021-10-20 18:05, jlarkin@highlandsniptechnology.com wrote: >>>> On Wed, 20 Oct 2021 17:59:06 +0200, Jeroen Belleman >>>> <jeroen@nospam.please> wrote: >>>> >>>>> On 2021-10-20 17:42, Dimiter_Popoff wrote: >>>>>> On 10/20/2021 5:20, jlarkin@highlandsniptechnology.com wrote: >>>>>>> I want to inject a 100 ps test pulse into a 50 ohm transmission line, >>>>>>> tee-wise, sometimes, from a 25 ohm source. So I need a series switch. >>>>>>> >>>>>>> I'd never paid much attention to PIN diodes... they are RF stuff. But >>>>>>> this one is shocking: >>>>>>> >>>>>>> https://www.mouser.com/datasheet/2/249/MADP_008120_12790T-1921620.pdf >>>>>>> >>>>>>> 2 ohms on, 0.14 pF off. >>>>>>> >>>>>>> And that's packaged. Chip and beam-lead parts are even better. >>>>>>> >>>>>>> Of course, in the long-honored RF tradition, there are no DC specs. No >>>>>>> hint of the forward conduction curve. A tiny note suggests that 10 mA, >>>>>>> 1 volt might happen. >>>>>>> >>>>>>> >>>>>>> >>>>>> >>>>>> Thanks for posting this John. I had been looking for something like >>>>>> that for a pulse generator I might want to build one day (after >>>>>> nearly 30 years this day may be coming closer...) and so far I >>>>>> had seen only parts with 1-2 V reverse voltage ability; this one >>>>>> seems to handle way more than I need. >>>>> >>>>> You do realize that it's not the PIN diode that makes the pulse, >>>>> right? A pin diode is merely a switch, and not even a very fast >>>>> one at that. >>>>> >>>>> Jeroen Belleman >>>> >>>> I have seen step-recovery effects in some PIN diodes, but it's rare >>>> and not very useful. I guess the intrinsic region doping profile can >>>> accidentally approach an SRD. Better to buy a real one. >>>> >>>> >>> >>> I honestly have no idea if PIN diodes for RF switching snap. >>> As a rule, they keep conducting for 100ns or so after reversal. >>> I didn't look in detail what happens then. Maybe I'm not curious >>> enough... >>> >>> I was quite happy to use them as RF switches with tiny parasitics. >>> (I would have used a reed, but the parasitic inductance turned >>> out to be too high in my application.) >>> >>> Jeroen Belleman >>> >>> >>> >> >> Ah! Now I understand what you were saying in the other message, >> I misunderstood your idea of "switching" (which in my mind was more >> like redirecting the current). 100ns turn off time is way too much >> for what I am after. > >Just to make sure we clear out any misunderstandings then, such >diodes are optimized to switch RF signals. With a fair amount of >forward current, the dynamic series resistance of the diode is >an ohm or two, so an RF signal can pass through. With a reverse >voltage of appropriate magnitude, the series impedance becomes >very high, and is dominated by a small capacitance, so the RF >signal can not pass. > > From the low impedance state, reverse recovery typically takes >about 100ns, so that down to 10MHz or so, even signals big enough >to drive the diode momentarily in reverse still see a low >impedance. > >PIN diodes aren't necessarily switches. They are also used in >continuously variable attenuators. > >PIN diodes exist from tiny SMD devices handling mW signals or >less, up to hefty power diodes switching multi-kW signals. > >The key to using PIN diodes as RF switches is how to separate >the switching current from the RF signal current, because both >must pass superimposed through the diode. > >Some rectifier diodes, although also called PIN diodes, are >completely different beasts. > >Jeroen Belleman >They may work as power RF switches too, if the capacitance isn't a killer. Some higher-voltage rectifiers are a PIN structure that can make a cool DSRD (drift step-recovery/Grehkov) diode. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
PIN diode
Started by ●October 19, 2021
Reply by ●October 20, 20212021-10-20
Reply by ●October 20, 20212021-10-20
On 21/10/21 6:18 am, John Larkin wrote:> On Wed, 20 Oct 2021 20:24:22 +0200, Gerhard Hoffmann <dk4xp@arcor.de> > wrote: > >> Am 20.10.21 um 19:52 schrieb John Larkin: >>> On Wed, 20 Oct 2021 18:05:10 +0200, Gerhard Hoffmann <dk4xp@arcor.de> >>> wrote: >>> >>>> >>>> No. the S-parameter tables give the conditions used for the measurement. >>> >>> >>> It's the only suggestion of DC operating point in the entire document. >>> Slightly better than nothing, I guess, generous by RF standards. >>> >>> This PIN data sheet has a Vf/If curve, absurdly wrong in the RF >>> tradition. >>> >>> https://www.digikey.com/en/products/detail/infineon-technologies/BA895E6327/12109715 >>> >>> The general tend seems to be high Vf and high reverse leakage. >> >> There is capacitance vs. backward voltage and resistance vs. forward >> current. On page 1. What else could one want? > > Voltage drop vs DC current. Diodes usually specify that, unless they > are "RF" parts. > >> Getting 20 mA forward current through a xyzzy diode is for beginners. > > Beginners with big power supplies.RF switches typically need to stay turned on for the whole cycle. If you want to pass 10mA of RF current, you need 20mA of DC, or more, depending on linearity requirements. Not very familiar with class-A, are you John? RF is almost all class-A. CH
Reply by ●October 20, 20212021-10-20
On 21/10/21 4:51 am, Dimiter_Popoff wrote:> On 10/20/2021 18:59, Jeroen Belleman wrote: >> On 2021-10-20 17:42, Dimiter_Popoff wrote: >>> On 10/20/2021 5:20, jlarkin@highlandsniptechnology.com wrote: >>>> I want to inject a 100 ps test pulse into a 50 ohm transmission line, >>>> tee-wise, sometimes, from a 25 ohm source. So I need a series switch. >>>> >>>> I'd never paid much attention to PIN diodes... they are RF stuff. But >>>> this one is shocking: >>>> >>>> https://www.mouser.com/datasheet/2/249/MADP_008120_12790T-1921620.pdf >>>> >>>> 2 ohms on, 0.14 pF off. >>>> >>>> And that's packaged. Chip and beam-lead parts are even better. >>>> >>>> Of course, in the long-honored RF tradition, there are no DC specs. No >>>> hint of the forward conduction curve. A tiny note suggests that 10 mA, >>>> 1 volt might happen. >>>> >>>> >>>> >>> >>> Thanks for posting this John. I had been looking for something like >>> that for a pulse generator I might want to build one day (after >>> nearly 30 years this day may be coming closer...) and so far I >>> had seen only parts with 1-2 V reverse voltage ability; this one >>> seems to handle way more than I need. >> >> You do realize that it's not the PIN diode that makes the pulse, >> right? A pin diode is merely a switch, and not even a very fast >> one at that. >> >> Jeroen Belleman > > Hey, I know what a diode is and have known how to switch currents > using diodes for well over 30 years :-). > The problem I hope it will solve is I will not inject too much > charge during the switching process, and at 1/4 pF (IIRC) this > will be the case, unless there are some unknown to me at this > point effects, similar to storage time for bipolars etc. >They achieve low capacitance by sweeping (slowly) all the charge carriers out of the intrinsic region, leaving a large gap between the conductors. Damn physics gets in the way of low-C and rapid switching. CH
Reply by ●October 20, 20212021-10-20
On 21/10/21 3:00 am, jlarkin@highlandsniptechnology.com wrote:> On Wed, 20 Oct 2021 18:42:53 +0300, Dimiter_Popoff <dp@tgi-sci.com> > wrote: > >> On 10/20/2021 5:20, jlarkin@highlandsniptechnology.com wrote: >>> I want to inject a 100 ps test pulse into a 50 ohm transmission line, >>> tee-wise, sometimes, from a 25 ohm source. So I need a series switch. >>> >>> I'd never paid much attention to PIN diodes... they are RF stuff. But >>> this one is shocking: >>> >>> https://www.mouser.com/datasheet/2/249/MADP_008120_12790T-1921620.pdf >>> >>> 2 ohms on, 0.14 pF off. >>> >>> And that's packaged. Chip and beam-lead parts are even better. >>> >>> Of course, in the long-honored RF tradition, there are no DC specs. No >>> hint of the forward conduction curve. A tiny note suggests that 10 mA, >>> 1 volt might happen. >>> >>> >>> >> >> Thanks for posting this John. I had been looking for something like >> that for a pulse generator I might want to build one day (after >> nearly 30 years this day may be coming closer...) and so far I >> had seen only parts with 1-2 V reverse voltage ability; this one >> seems to handle way more than I need. > > Yeah, the specs shocked me, after struggling to do this with a > schottky. The carrier lifetime could be a problem with long pulses. > > I love pulse generators. Let me know if I can help. > > There are all sorts of cheap fungens and scopes and such, but pulse > generators are generally still mediocre and expensive. I want to do > one myself some day, a really fast version of our DDG.There is plenty of excitement around the NanoVNA and the TinySA. It's time to do a TinyTDR. Bet you'd sell many thousands. If you do the pulse gen and the sampler I'll do the rest. Clifford Heath
Reply by ●October 20, 20212021-10-20
Am 20.10.21 um 23:34 schrieb Clifford Heath:> On 21/10/21 6:18 am, John Larkin wrote: >> On Wed, 20 Oct 2021 20:24:22 +0200, Gerhard Hoffmann <dk4xp@arcor.de>>>> Getting 20 mA forward current through a xyzzy diode is for beginners. >> >> Beginners with big power supplies. > > RF switches typically need to stay turned on for the whole cycle. If you > want to pass 10mA of RF current, you need 20mA of DC, or more, depending > on linearity requirements.There is no way around the 20mA. It is needed that the serial resistance goes below 2 Ohms. The ds says that the instrinsic zone is 19 um thick. That is more than the copper thickness of my multilayers. That is the reason for the low capacitance. It is also the reason for the slow switching. The 19 um must first be filled with carriers before the onset of conductance. And when switching off, the carriers must be removed from the I zone. When it is empty, the resistance rises suddenly. Snap-off diodes are optimized that the carriers are all gone at the same time. At low frequencies (few MHz) these PIN-Ds act like normal diodes. Then they do NOT behave like resistors. PIN attenuators create IMD at low frequencies. That is not their habit at uwave frequencies. There are some diodes usable down to 1 MHz, but not cheap. Growing the long I zone probably costs a lot. cheers, Gerhard
Reply by ●October 20, 20212021-10-20
onsdag den 20. oktober 2021 kl. 23.34.17 UTC+2 skrev Clifford Heath:> On 21/10/21 6:18 am, John Larkin wrote: > > On Wed, 20 Oct 2021 20:24:22 +0200, Gerhard Hoffmann <dk...@arcor.de> > > wrote: > > > >> Am 20.10.21 um 19:52 schrieb John Larkin: > >>> On Wed, 20 Oct 2021 18:05:10 +0200, Gerhard Hoffmann <dk...@arcor.de> > >>> wrote: > >>> > >>>> > >>>> No. the S-parameter tables give the conditions used for the measurement. > >>> > >>> > >>> It's the only suggestion of DC operating point in the entire document. > >>> Slightly better than nothing, I guess, generous by RF standards. > >>> > >>> This PIN data sheet has a Vf/If curve, absurdly wrong in the RF > >>> tradition. > >>> > >>> https://www.digikey.com/en/products/detail/infineon-technologies/BA895E6327/12109715 > >>> > >>> The general tend seems to be high Vf and high reverse leakage. > >> > >> There is capacitance vs. backward voltage and resistance vs. forward > >> current. On page 1. What else could one want? > > > > Voltage drop vs DC current. Diodes usually specify that, unless they > > are "RF" parts. > > > >> Getting 20 mA forward current through a xyzzy diode is for beginners. > > > > Beginners with big power supplies. > RF switches typically need to stay turned on for the whole cycle. If you > want to pass 10mA of RF current, you need 20mA of DC, or more, depending > on linearity requirements.sure about that? if the frequency is low and/or you are using regular silicon diodes, sure but for pin diodes at high frequencies?
Reply by ●October 20, 20212021-10-20
On Wed, 20 Oct 2021 13:09:01 -0700, John Larkin <jlarkin@highland_atwork_technology.com> wrote:>On Wed, 20 Oct 2021 14:50:53 -0400, legg <legg@nospam.magma.ca> wrote: > >>On Tue, 19 Oct 2021 19:20:04 -0700, jlarkin@highlandsniptechnology.com >>wrote: >> >>>I want to inject a 100 ps test pulse into a 50 ohm transmission line, >>>tee-wise, sometimes, from a 25 ohm source. So I need a series switch. >>> >>>I'd never paid much attention to PIN diodes... they are RF stuff. But >>>this one is shocking: >>> >>>https://www.mouser.com/datasheet/2/249/MADP_008120_12790T-1921620.pdf >>> >>>2 ohms on, 0.14 pF off. >>> >>>And that's packaged. Chip and beam-lead parts are even better. >>> >>>Of course, in the long-honored RF tradition, there are no DC specs. No >>>hint of the forward conduction curve. A tiny note suggests that 10 mA, >>>1 volt might happen. >> >>What's so special? >> >>A simple re-sort of smd marking files by function, voltage and >>current, pulls up quite a few similar or superior devices. >> >>http://ve3ute.ca/query/smd_PIN_V_A_210810E.zip >> >>RL > >The amps and volts numbers appear to be abs max, forward current and >reverse voltage. That tells nothing about the conduction curve. > >RF!You mean the 'R' values . . . ? I'd assumed you were praising C and R specs. You can sort for those. They're a start. For a nominal V/I plot, you'd have to get the datasheet. Nominal plots aren't much use in design, where every part used has to work. RL
Reply by ●October 20, 20212021-10-20
On Thu, 21 Oct 2021 08:34:09 +1100, Clifford Heath <no.spam@please.net> wrote:>On 21/10/21 6:18 am, John Larkin wrote: >> On Wed, 20 Oct 2021 20:24:22 +0200, Gerhard Hoffmann <dk4xp@arcor.de> >> wrote: >> >>> Am 20.10.21 um 19:52 schrieb John Larkin: >>>> On Wed, 20 Oct 2021 18:05:10 +0200, Gerhard Hoffmann <dk4xp@arcor.de> >>>> wrote: >>>> >>>>> >>>>> No. the S-parameter tables give the conditions used for the measurement. >>>> >>>> >>>> It's the only suggestion of DC operating point in the entire document. >>>> Slightly better than nothing, I guess, generous by RF standards. >>>> >>>> This PIN data sheet has a Vf/If curve, absurdly wrong in the RF >>>> tradition. >>>> >>>> https://www.digikey.com/en/products/detail/infineon-technologies/BA895E6327/12109715 >>>> >>>> The general tend seems to be high Vf and high reverse leakage. >>> >>> There is capacitance vs. backward voltage and resistance vs. forward >>> current. On page 1. What else could one want? >> >> Voltage drop vs DC current. Diodes usually specify that, unless they >> are "RF" parts. >> >>> Getting 20 mA forward current through a xyzzy diode is for beginners. >> >> Beginners with big power supplies. > >RF switches typically need to stay turned on for the whole cycle. If you >want to pass 10mA of RF current, you need 20mA of DC, or more, depending >on linearity requirements. > >Not very familiar with class-A, are you John? RF is almost all class-A. > >CHOne virtue of PIN diodes is that a very little DC current can switch a lot of RF current. Not very familiar with semiconductors, are you? -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
Reply by ●October 20, 20212021-10-20
On Thu, 21 Oct 2021 00:22:10 +0200, Gerhard Hoffmann <dk4xp@arcor.de> wrote:>Am 20.10.21 um 23:34 schrieb Clifford Heath: >> On 21/10/21 6:18 am, John Larkin wrote: >>> On Wed, 20 Oct 2021 20:24:22 +0200, Gerhard Hoffmann <dk4xp@arcor.de> > >>>> Getting 20 mA forward current through a xyzzy diode is for beginners. >>> >>> Beginners with big power supplies. >> >> RF switches typically need to stay turned on for the whole cycle. If you >> want to pass 10mA of RF current, you need 20mA of DC, or more, depending >> on linearity requirements. > >There is no way around the 20mA. It is needed that the serial resistance >goes below 2 Ohms. >A pin diode doesn't quit conducting when the current reverses. That's the point of the thick I region with a long charge recombination lifetime. A little DC current can switch a lot of RF current. The Macom part that I cited is under 2 ohms RF resistance at 100 MHz and 10 mA DC. The RF current is limited by power dissipation. Which, of sourse, they don't specify. Without useful data and without Spice models, I suppose people design around these parts by fiddling. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
Reply by ●October 20, 20212021-10-20
On Thu, 21 Oct 2021 08:41:39 +1100, Clifford Heath <no.spam@please.net> wrote:>On 21/10/21 3:00 am, jlarkin@highlandsniptechnology.com wrote: >> On Wed, 20 Oct 2021 18:42:53 +0300, Dimiter_Popoff <dp@tgi-sci.com> >> wrote: >> >>> On 10/20/2021 5:20, jlarkin@highlandsniptechnology.com wrote: >>>> I want to inject a 100 ps test pulse into a 50 ohm transmission line, >>>> tee-wise, sometimes, from a 25 ohm source. So I need a series switch. >>>> >>>> I'd never paid much attention to PIN diodes... they are RF stuff. But >>>> this one is shocking: >>>> >>>> https://www.mouser.com/datasheet/2/249/MADP_008120_12790T-1921620.pdf >>>> >>>> 2 ohms on, 0.14 pF off. >>>> >>>> And that's packaged. Chip and beam-lead parts are even better. >>>> >>>> Of course, in the long-honored RF tradition, there are no DC specs. No >>>> hint of the forward conduction curve. A tiny note suggests that 10 mA, >>>> 1 volt might happen. >>>> >>>> >>>> >>> >>> Thanks for posting this John. I had been looking for something like >>> that for a pulse generator I might want to build one day (after >>> nearly 30 years this day may be coming closer...) and so far I >>> had seen only parts with 1-2 V reverse voltage ability; this one >>> seems to handle way more than I need. >> >> Yeah, the specs shocked me, after struggling to do this with a >> schottky. The carrier lifetime could be a problem with long pulses. >> >> I love pulse generators. Let me know if I can help. >> >> There are all sorts of cheap fungens and scopes and such, but pulse >> generators are generally still mediocre and expensive. I want to do >> one myself some day, a really fast version of our DDG. > >There is plenty of excitement around the NanoVNA and the TinySA. >It's time to do a TinyTDR. Bet you'd sell many thousands. If you do the >pulse gen and the sampler I'll do the rest. > >Clifford HeathI have around here somewhere a proto PCB that has a pretty fast, reasonably cheap TDR circuit. It seemed to work but I haven't had time to really play with it. It would need a DAC and an ADC and a lot of code to make a sellable instrument. I also have a deconvolution algorithm that makes an ugly ringy TDR into a beautiful TDR. That's key to doing TDR easily with Digikey parts on FR4. https://www.dropbox.com/s/iqpldbkq2awdeml/TDR_Decon_demo.jpg?raw=1 Pretend the yellow trace is the nasty TDR hardware response. The purple trace is the impulse response of the filter which when convolved with the ugly one turns it into the perfect white one. You can't see the green target waveform because the white processed one perfectly overlays it. My code computes the required FIR filter. This is the ill-posed deconvolution problem. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
