Phil Hobbs wrote:> On 02/17/2014 01:55 AM, miso wrote: >> Phil Hobbs wrote: >> >>> 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 >>> >> >> I'm all ears for the dual gate MOSFET trick. Are they using one of the >> gates >> to shield the charge injection of the other gate? >> >> Back in the day, much effort went into complimentary switches in charge >> transfer circuits. All sorts of games regarding clock rates (not too >> fast, >> not to slow), etc. >> >> > It's pretty simple--you connect the input to the source and G2, storage > cap to D, sample pulse to G1. (It works best with parts that bias > properly with V_G2S = 0.) Works great with 3N201s. ;) > > You usually wouldn't do it that way because of the resistance > nonlinearity, but you don't care much about that in a sampler, assuming > the sample gate is several time constants wide. >Unfortunately it hardly ever is. Mostly the time constant is 10x to 100x the sample gate width. So one either has to live just with the small delta-V as a sampled signal for processing or let this run over a hundred cycles or so and accumulate in a post sampler. Or use the feedback trick from the old HP days that John described to make the sampler cap ratchet up. The ratcheting should be easier with the dual-gate circuit though because there won't be any leakage. Might not even need the feedback or post-sampling at all. But capacitances are probably quite high, or at least higher than 0.25pF. Possibly the nonlinearityy could be servoed out by running a 2nd dual-gate in a slower fashion. That's how I sometimes did controllable delay circuits. It would be nice to have a dual-dual-gate FET for that but having them close to each other with some serious copper on the inner layers could work. -- Regards, Joerg http://www.analogconsultants.com/
Sampler diodes with more barrier height?
Started by ●February 15, 2014
Reply by ●February 17, 20142014-02-17
Reply by ●February 17, 20142014-02-17
On 02/17/2014 10:20 AM, Joerg wrote:> Phil Hobbs wrote: >> On 02/17/2014 01:55 AM, miso wrote: >>> Phil Hobbs wrote: >>> >>>> 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 >>>> >>> >>> I'm all ears for the dual gate MOSFET trick. Are they using one of the >>> gates >>> to shield the charge injection of the other gate? >>> >>> Back in the day, much effort went into complimentary switches in charge >>> transfer circuits. All sorts of games regarding clock rates (not too >>> fast, >>> not to slow), etc. >>> >>> >> It's pretty simple--you connect the input to the source and G2, storage >> cap to D, sample pulse to G1. (It works best with parts that bias >> properly with V_G2S = 0.) Works great with 3N201s. ;) >> >> You usually wouldn't do it that way because of the resistance >> nonlinearity, but you don't care much about that in a sampler, assuming >> the sample gate is several time constants wide. >> > > Unfortunately it hardly ever is. Mostly the time constant is 10x to 100x > the sample gate width. So one either has to live just with the small > delta-V as a sampled signal for processing or let this run over a > hundred cycles or so and accumulate in a post sampler. Or use the > feedback trick from the old HP days that John described to make the > sampler cap ratchet up. > > The ratcheting should be easier with the dual-gate circuit though > because there won't be any leakage. Might not even need the feedback or > post-sampling at all. But capacitances are probably quite high, or at > least higher than 0.25pF. > > Possibly the nonlinearityy could be servoed out by running a 2nd > dual-gate in a slower fashion. That's how I sometimes did controllable > delay circuits. It would be nice to have a dual-dual-gate FET for that > but having them close to each other with some serious copper on the > inner layers could work. >Right, it's the second sampler I'm talking about. Normally getting a 100-ns TC and a 1-us window isn't so hard. In a fast sampler running inside a sampling loop (where the previous sample is added to the bias voltages), the diode conditions are kept pretty nearly constant from sample to sample. 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
Reply by ●February 17, 20142014-02-17
Phil Hobbs wrote:> On 02/17/2014 10:20 AM, Joerg wrote: >> Phil Hobbs wrote: >>> On 02/17/2014 01:55 AM, miso wrote: >>>> Phil Hobbs wrote: >>>> >>>>> 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 >>>>> >>>> >>>> I'm all ears for the dual gate MOSFET trick. Are they using one of the >>>> gates >>>> to shield the charge injection of the other gate? >>>> >>>> Back in the day, much effort went into complimentary switches in charge >>>> transfer circuits. All sorts of games regarding clock rates (not too >>>> fast, >>>> not to slow), etc. >>>> >>>> >>> It's pretty simple--you connect the input to the source and G2, storage >>> cap to D, sample pulse to G1. (It works best with parts that bias >>> properly with V_G2S = 0.) Works great with 3N201s. ;) >>> >>> You usually wouldn't do it that way because of the resistance >>> nonlinearity, but you don't care much about that in a sampler, assuming >>> the sample gate is several time constants wide. >>> >> >> Unfortunately it hardly ever is. Mostly the time constant is 10x to 100x >> the sample gate width. So one either has to live just with the small >> delta-V as a sampled signal for processing or let this run over a >> hundred cycles or so and accumulate in a post sampler. Or use the >> feedback trick from the old HP days that John described to make the >> sampler cap ratchet up. >> >> The ratcheting should be easier with the dual-gate circuit though >> because there won't be any leakage. Might not even need the feedback or >> post-sampling at all. But capacitances are probably quite high, or at >> least higher than 0.25pF. >> >> Possibly the nonlinearityy could be servoed out by running a 2nd >> dual-gate in a slower fashion. That's how I sometimes did controllable >> delay circuits. It would be nice to have a dual-dual-gate FET for that >> but having them close to each other with some serious copper on the >> inner layers could work. >> > > Right, it's the second sampler I'm talking about. Normally getting a > 100-ns TC and a 1-us window isn't so hard. >Looks like I may have to live with single-diode and then there's only a few tens of nsec available. It might have to be discrete again since even what they call fast (ADG820 and similar) isn't that great in speed. At least in the reasonable price range.> In a fast sampler running inside a sampling loop (where the previous > sample is added to the bias voltages), the diode conditions are kept > pretty nearly constant from sample to sample. >Or one just lives with the delta-V without a loop. Could be averaged locally or digitally later since AD converters have become so cheap. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●February 17, 20142014-02-17
On 02/17/2014 11:05 AM, Joerg wrote:> Phil Hobbs wrote: >> On 02/17/2014 10:20 AM, Joerg wrote: >>> Phil Hobbs wrote: >>>> On 02/17/2014 01:55 AM, miso wrote: >>>>> Phil Hobbs wrote: >>>>> >>>>>> 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 >>>>>> >>>>> >>>>> I'm all ears for the dual gate MOSFET trick. Are they using one of the >>>>> gates >>>>> to shield the charge injection of the other gate? >>>>> >>>>> Back in the day, much effort went into complimentary switches in charge >>>>> transfer circuits. All sorts of games regarding clock rates (not too >>>>> fast, >>>>> not to slow), etc. >>>>> >>>>> >>>> It's pretty simple--you connect the input to the source and G2, storage >>>> cap to D, sample pulse to G1. (It works best with parts that bias >>>> properly with V_G2S = 0.) Works great with 3N201s. ;) >>>> >>>> You usually wouldn't do it that way because of the resistance >>>> nonlinearity, but you don't care much about that in a sampler, assuming >>>> the sample gate is several time constants wide. >>>> >>> >>> Unfortunately it hardly ever is. Mostly the time constant is 10x to 100x >>> the sample gate width. So one either has to live just with the small >>> delta-V as a sampled signal for processing or let this run over a >>> hundred cycles or so and accumulate in a post sampler. Or use the >>> feedback trick from the old HP days that John described to make the >>> sampler cap ratchet up. >>> >>> The ratcheting should be easier with the dual-gate circuit though >>> because there won't be any leakage. Might not even need the feedback or >>> post-sampling at all. But capacitances are probably quite high, or at >>> least higher than 0.25pF. >>> >>> Possibly the nonlinearityy could be servoed out by running a 2nd >>> dual-gate in a slower fashion. That's how I sometimes did controllable >>> delay circuits. It would be nice to have a dual-dual-gate FET for that >>> but having them close to each other with some serious copper on the >>> inner layers could work. >>> >> >> Right, it's the second sampler I'm talking about. Normally getting a >> 100-ns TC and a 1-us window isn't so hard. >> > > Looks like I may have to live with single-diode and then there's only a > few tens of nsec available. It might have to be discrete again since > even what they call fast (ADG820 and similar) isn't that great in speed. > At least in the reasonable price range. > > >> In a fast sampler running inside a sampling loop (where the previous >> sample is added to the bias voltages), the diode conditions are kept >> pretty nearly constant from sample to sample. >> > > Or one just lives with the delta-V without a loop. Could be averaged > locally or digitally later since AD converters have become so cheap. >Assuming that one has a sufficiently accurate model of diode behaviour under dynamic conditions. Feedback is nice that way. A BF908 has a reverse transfer capacitance (G1-D) of typically 0.03 pF. The G2-D capacitance would be more of a worry, but one more cascode stage should fix that. I'll have to build one of those one of these days--I haven't used one in about three zillion years. 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
Reply by ●February 17, 20142014-02-17
On Sunday, February 16, 2014 9:35:42 PM UTC-5, John Larkin wrote:> > Nothing that you'd ever be involved with. >...and you either from what I can see...
Reply by ●February 17, 20142014-02-17
On 02/17/2014 11:25 AM, Phil Hobbs wrote:> On 02/17/2014 11:05 AM, Joerg wrote: >> Phil Hobbs wrote: >>> On 02/17/2014 10:20 AM, Joerg wrote: >>>> Phil Hobbs wrote: >>>>> On 02/17/2014 01:55 AM, miso wrote: >>>>>> Phil Hobbs wrote: >>>>>> >>>>>>> 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 >>>>>>> >>>>>> >>>>>> I'm all ears for the dual gate MOSFET trick. Are they using one of >>>>>> the >>>>>> gates >>>>>> to shield the charge injection of the other gate? >>>>>> >>>>>> Back in the day, much effort went into complimentary switches in >>>>>> charge >>>>>> transfer circuits. All sorts of games regarding clock rates (not too >>>>>> fast, >>>>>> not to slow), etc. >>>>>> >>>>>> >>>>> It's pretty simple--you connect the input to the source and G2, >>>>> storage >>>>> cap to D, sample pulse to G1. (It works best with parts that bias >>>>> properly with V_G2S = 0.) Works great with 3N201s. ;) >>>>> >>>>> You usually wouldn't do it that way because of the resistance >>>>> nonlinearity, but you don't care much about that in a sampler, >>>>> assuming >>>>> the sample gate is several time constants wide. >>>>> >>>> >>>> Unfortunately it hardly ever is. Mostly the time constant is 10x to >>>> 100x >>>> the sample gate width. So one either has to live just with the small >>>> delta-V as a sampled signal for processing or let this run over a >>>> hundred cycles or so and accumulate in a post sampler. Or use the >>>> feedback trick from the old HP days that John described to make the >>>> sampler cap ratchet up. >>>> >>>> The ratcheting should be easier with the dual-gate circuit though >>>> because there won't be any leakage. Might not even need the feedback or >>>> post-sampling at all. But capacitances are probably quite high, or at >>>> least higher than 0.25pF. >>>> >>>> Possibly the nonlinearityy could be servoed out by running a 2nd >>>> dual-gate in a slower fashion. That's how I sometimes did controllable >>>> delay circuits. It would be nice to have a dual-dual-gate FET for that >>>> but having them close to each other with some serious copper on the >>>> inner layers could work. >>>> >>> >>> Right, it's the second sampler I'm talking about. Normally getting a >>> 100-ns TC and a 1-us window isn't so hard. >>> >> >> Looks like I may have to live with single-diode and then there's only a >> few tens of nsec available. It might have to be discrete again since >> even what they call fast (ADG820 and similar) isn't that great in speed. >> At least in the reasonable price range. >> >> >>> In a fast sampler running inside a sampling loop (where the previous >>> sample is added to the bias voltages), the diode conditions are kept >>> pretty nearly constant from sample to sample. >>> >> >> Or one just lives with the delta-V without a loop. Could be averaged >> locally or digitally later since AD converters have become so cheap. >> > > Assuming that one has a sufficiently accurate model of diode behaviour > under dynamic conditions. Feedback is nice that way. > > A BF908 has a reverse transfer capacitance (G1-D) of typically 0.03 pF. > The G2-D capacitance would be more of a worry, but one more cascode > stage should fix that.Or run G2 from the buffer output, which would also fix it. Have to try that. 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
Reply by ●February 17, 20142014-02-17
Phil Hobbs wrote:> On 02/17/2014 11:25 AM, Phil Hobbs wrote: >> On 02/17/2014 11:05 AM, Joerg wrote: >>> Phil Hobbs wrote: >>>> On 02/17/2014 10:20 AM, Joerg wrote: >>>>> Phil Hobbs wrote: >>>>>> On 02/17/2014 01:55 AM, miso wrote: >>>>>>> Phil Hobbs wrote: >>>>>>> >>>>>>>> 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 >>>>>>>> >>>>>>> >>>>>>> I'm all ears for the dual gate MOSFET trick. Are they using one of >>>>>>> the >>>>>>> gates >>>>>>> to shield the charge injection of the other gate? >>>>>>> >>>>>>> Back in the day, much effort went into complimentary switches in >>>>>>> charge >>>>>>> transfer circuits. All sorts of games regarding clock rates (not too >>>>>>> fast, >>>>>>> not to slow), etc. >>>>>>> >>>>>>> >>>>>> It's pretty simple--you connect the input to the source and G2, >>>>>> storage >>>>>> cap to D, sample pulse to G1. (It works best with parts that bias >>>>>> properly with V_G2S = 0.) Works great with 3N201s. ;) >>>>>> >>>>>> You usually wouldn't do it that way because of the resistance >>>>>> nonlinearity, but you don't care much about that in a sampler, >>>>>> assuming >>>>>> the sample gate is several time constants wide. >>>>>> >>>>> >>>>> Unfortunately it hardly ever is. Mostly the time constant is 10x to >>>>> 100x >>>>> the sample gate width. So one either has to live just with the small >>>>> delta-V as a sampled signal for processing or let this run over a >>>>> hundred cycles or so and accumulate in a post sampler. Or use the >>>>> feedback trick from the old HP days that John described to make the >>>>> sampler cap ratchet up. >>>>> >>>>> The ratcheting should be easier with the dual-gate circuit though >>>>> because there won't be any leakage. Might not even need the >>>>> feedback or >>>>> post-sampling at all. But capacitances are probably quite high, or at >>>>> least higher than 0.25pF. >>>>> >>>>> Possibly the nonlinearityy could be servoed out by running a 2nd >>>>> dual-gate in a slower fashion. That's how I sometimes did controllable >>>>> delay circuits. It would be nice to have a dual-dual-gate FET for that >>>>> but having them close to each other with some serious copper on the >>>>> inner layers could work. >>>>> >>>> >>>> Right, it's the second sampler I'm talking about. Normally getting a >>>> 100-ns TC and a 1-us window isn't so hard. >>>> >>> >>> Looks like I may have to live with single-diode and then there's only a >>> few tens of nsec available. It might have to be discrete again since >>> even what they call fast (ADG820 and similar) isn't that great in speed. >>> At least in the reasonable price range. >>> >>> >>>> In a fast sampler running inside a sampling loop (where the previous >>>> sample is added to the bias voltages), the diode conditions are kept >>>> pretty nearly constant from sample to sample. >>>> >>> >>> Or one just lives with the delta-V without a loop. Could be averaged >>> locally or digitally later since AD converters have become so cheap. >>> >> >> Assuming that one has a sufficiently accurate model of diode behaviour >> under dynamic conditions. Feedback is nice that way. >> >> A BF908 has a reverse transfer capacitance (G1-D) of typically 0.03 pF. >> The G2-D capacitance would be more of a worry, but one more cascode >> stage should fix that. > > Or run G2 from the buffer output, which would also fix it. Have to try > that. >True, but if you need a buffer or a charge amp with a beefy output you might as well use a Schottky diode there, too :-) -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●February 17, 20142014-02-17
On Mon, 17 Feb 2014 08:34:44 -0800 (PST), bloggs.fredbloggs.fred@gmail.com wrote:>On Sunday, February 16, 2014 9:35:42 PM UTC-5, John Larkin wrote: > >> >> Nothing that you'd ever be involved with. >> > >...and you either from what I can see...I use sampling scopes all the time, and have a modest collection of antiques and manuals. I have an actual Lumatron box https://dl.dropboxusercontent.com/u/53724080/Sampling/Lumatron.jpg (single point-contact diode sampler, avalanche transistor, hideous but historical) and a Tek type N plugin (also single diode, but pretty) and a 1S1 and a 1S2 https://dl.dropboxusercontent.com/u/53724080/Sampling/1S2-547.jpg The 1S2 was a wonderful gadget; I learned a lot about picosecond electronics from that plugin. A bunch of HP stuff, too https://dl.dropboxusercontent.com/u/53724080/Sampling/HP/1430guts.jpg https://dl.dropboxusercontent.com/u/53724080/Sampling/HP/HP185/188head3.jpg https://dl.dropboxusercontent.com/u/53724080/Sampling/HP/HP185/training2.jpg On my bench I have a Tek 11802 with a bunch of sampling heads. The SD24 head does 20 GHz sampling/TDR and, as Phil says, it makes a good picosecond pulse generator, too. I recently got a 50 GHz head (SD32?) from ebay. Seems fine. I built a 2-diode sampler, similar to my sketch, and it worked fine. Tr was about 70 ps, which is around 5 GHz. https://dl.dropboxusercontent.com/u/53724080/Sampling/Sampler1.JPG A 20 GHz sampler is feasible with surface-mount parts on FR4... I've seen it done. It would be great fun to go into the sampler business, but it's hard to compete with all the gear on ebay. Anybody who wants to get good at picosecond electronics can do it for $1000 and some time. This was probably the world's first sampling oscilloscope: https://dl.dropboxusercontent.com/u/53724080/Sampling/ondo.gif Here's Mark Kahr's superb paper on the history of sampling scopes: https://dl.dropboxusercontent.com/u/53724080/Sampling/MarkMTT.pdf -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
Reply by ●February 17, 20142014-02-17
On Mon, 17 Feb 2014 08:05:06 -0800, Joerg <invalid@invalid.invalid> wrote:>Phil Hobbs wrote: >> On 02/17/2014 10:20 AM, Joerg wrote: >>> Phil Hobbs wrote: >>>> On 02/17/2014 01:55 AM, miso wrote: >>>>> Phil Hobbs wrote: >>>>> >>>>>> 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 >>>>>> >>>>> >>>>> I'm all ears for the dual gate MOSFET trick. Are they using one of the >>>>> gates >>>>> to shield the charge injection of the other gate? >>>>> >>>>> Back in the day, much effort went into complimentary switches in charge >>>>> transfer circuits. All sorts of games regarding clock rates (not too >>>>> fast, >>>>> not to slow), etc. >>>>> >>>>> >>>> It's pretty simple--you connect the input to the source and G2, storage >>>> cap to D, sample pulse to G1. (It works best with parts that bias >>>> properly with V_G2S = 0.) Works great with 3N201s. ;) >>>> >>>> You usually wouldn't do it that way because of the resistance >>>> nonlinearity, but you don't care much about that in a sampler, assuming >>>> the sample gate is several time constants wide. >>>> >>> >>> Unfortunately it hardly ever is. Mostly the time constant is 10x to 100x >>> the sample gate width. So one either has to live just with the small >>> delta-V as a sampled signal for processing or let this run over a >>> hundred cycles or so and accumulate in a post sampler. Or use the >>> feedback trick from the old HP days that John described to make the >>> sampler cap ratchet up. >>> >>> The ratcheting should be easier with the dual-gate circuit though >>> because there won't be any leakage. Might not even need the feedback or >>> post-sampling at all. But capacitances are probably quite high, or at >>> least higher than 0.25pF. >>> >>> Possibly the nonlinearityy could be servoed out by running a 2nd >>> dual-gate in a slower fashion. That's how I sometimes did controllable >>> delay circuits. It would be nice to have a dual-dual-gate FET for that >>> but having them close to each other with some serious copper on the >>> inner layers could work. >>> >> >> Right, it's the second sampler I'm talking about. Normally getting a >> 100-ns TC and a 1-us window isn't so hard. >> > >Looks like I may have to live with single-diode and then there's only a >few tens of nsec available. It might have to be discrete again since >even what they call fast (ADG820 and similar) isn't that great in speed. >At least in the reasonable price range. > > >> In a fast sampler running inside a sampling loop (where the previous >> sample is added to the bias voltages), the diode conditions are kept >> pretty nearly constant from sample to sample. >> > >Or one just lives with the delta-V without a loop. Could be averaged >locally or digitally later since AD converters have become so cheap.One problem with the single-diode sampler is that variations in the sampling pulse height rip right through with the signal, which can get noisy. And it tends to be nonlinear. And there is a huge kickout of the sampling pulse to the input connector. The old Lumatron boxes, and the Tektronix N, were single-diode samplers with avalanche transistor strobe generators. They were fairly nasty. LeCroy did a single-diode sampler a while back but discontinued it. LeCroy did a lot of weird things, like their untriggered DDS timebase for telecom eye diagrams. It would be interesting to see what could be done with MiniCircuits parts (baluns and mixers) to make an open-loop bridge sampler. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
Reply by ●February 17, 20142014-02-17
John Larkin wrote:> On Mon, 17 Feb 2014 08:05:06 -0800, Joerg <invalid@invalid.invalid> wrote: > >> Phil Hobbs wrote:[...]>> >>> In a fast sampler running inside a sampling loop (where the previous >>> sample is added to the bias voltages), the diode conditions are kept >>> pretty nearly constant from sample to sample. >>> >> Or one just lives with the delta-V without a loop. Could be averaged >> locally or digitally later since AD converters have become so cheap. > > One problem with the single-diode sampler is that variations in the sampling > pulse height rip right through with the signal, which can get noisy. And it > tends to be nonlinear. And there is a huge kickout of the sampling pulse to the > input connector. >Yes, those are generally the downsides. But the sampling pulse can be kept fairly constant and calculated out. The kickout is huge because the sampling pulse roars right through the diode capacitance. But in equivalent time samplers that is mostly just an EMC concern. Provided that the load does not go berserk upon being hit with the kickout.> The old Lumatron boxes, and the Tektronix N, were single-diode samplers with > avalanche transistor strobe generators. They were fairly nasty. LeCroy did a > single-diode sampler a while back but discontinued it. LeCroy did a lot of weird > things, like their untriggered DDS timebase for telecom eye diagrams. >Luckily my stuff doesn't need to be high precision but it has to be cheap and small. For samplers it's truly slim pickens. Just now looking for something useful for the post-sampler. All the commercial S&H chips I saw so far are slow as snails, even the pricey ones.> It would be interesting to see what could be done with MiniCircuits parts > (baluns and mixers) to make an open-loop bridge sampler. >I mostly came away disappointed when canvassing the commercial offerings. That was the same during my masters project in the mid-80's. I was designing a CCD camera that would beat the daylights out of the camera the CCD manufacturer was offering (and it did). After a frustrating search I just wound my own bridge sampler transformers. Which I should have done in the first place, would have saved me time. For the diodes I used matched quads, I believe from HP. Four individual diodes per pouch. -- Regards, Joerg http://www.analogconsultants.com/
