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PIN diode

Started by Unknown October 19, 2021
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
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.
On 10/20/2021 21:02, John Larkin wrote:
> On Wed, 20 Oct 2021 20:51:32 +0300, Dimiter_Popoff <dp@tgi-sci.com> > 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. > > Pins will switch fast signals, but turning the switch on/off is slow, > so they can't *make* fast signals. > > There are potentially useful GHz-speed IC switches, but the switch > times are terrible. > > Making fast pulses still requires lots of parts on boards, > old-fashioned circuit design. > > > >
I am not after your ps range pulses stuff, never been there (yet). It is ns range current switching, I had found some diodes (I think again after something you had posted) which are good but the voltages between which I have to switch the current are inconvenient, doable though. Will keep on looking, no rush after 30 years of waiting :-). Meantime my pulser is still a mercury wetted relay based, about 30 years old.
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? Getting 20 mA forward current through a xyzzy diode is for beginners. Gerhard
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
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. -- 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
On Wed, 20 Oct 2021 21:15:12 +0300, Dimiter_Popoff <dp@tgi-sci.com>
wrote:

>On 10/20/2021 21:02, John Larkin wrote: >> On Wed, 20 Oct 2021 20:51:32 +0300, Dimiter_Popoff <dp@tgi-sci.com> >> 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. >> >> Pins will switch fast signals, but turning the switch on/off is slow, >> so they can't *make* fast signals. >> >> There are potentially useful GHz-speed IC switches, but the switch >> times are terrible. >> >> Making fast pulses still requires lots of parts on boards, >> old-fashioned circuit design. >> >> >> >> > >I am not after your ps range pulses stuff, never been there (yet). >It is ns range current switching, I had found some diodes (I think >again after something you had posted) which are good but the voltages >between which I have to switch the current are inconvenient, doable >though. Will keep on looking, no rush after 30 years of waiting :-). >Meantime my pulser is still a mercury wetted relay based, about >30 years old.
The tiny EPC GaN fets can switch 10s of volts in under 1 ns. MiniCircuits SAV-series parts are cool, to about 10 volts. Laser drivers are fun, like the Leo Bodnar thing. -- 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
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! -- 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
On 10/20/2021 22:22, John Larkin wrote:
> On Wed, 20 Oct 2021 21:11:12 +0300, Dimiter_Popoff <dp@tgi-sci.com> > 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. > > Treat it like a tiny relay. > > Phemts can be truly fast switches, parts like SAV541. >
I get it now that Jeroen said about the 100ns turn off time, I am not an RF person so when I hear of a fast diode I think fast switching, not HF insulation capability with slow switching, did not even know this was on offer :-). I have looked at various diodes, the one in the .asc file now is some SMS7630 which looks good (last time I have checked it was about a year ago). If this diode sounds familiar to you chances are I have seen it in one of your posts. This pulser has been in the state "this interesting part hit me, perhaps I could use it for it" for decades now...
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