RF Transistor Noise Source
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From: Jim Thompson on 29 Dec 2009 15:14 On Tue, 29 Dec 2009 10:05:26 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 29 Dec 2009 00:43:19 -0800, Robert Baer ><robertbaer(a)localnet.com> wrote: > >>RST Engineering wrote: >>> . >>> . >>> There was a general discussion in this NG a couple of weeks ago about >>> using a lightly-biased zener as a noise source. There was no clear >>> definition about how flat or to what frequency the noise was useful. >>> >>> It got me to thinking and I'll do the experiment as soon as I can >>> clean off my bench, but what do you think I'm going to see for >>> reasonable noise bandwidth if I use a small signal (like a 2N5770 or >>> 918) and use the emitter-base junction as the zener. Most of them >>> zener somewhere around 5 volts and that should be reasonable. >>> >>> Most of the comments regarding bandwidth using a "regular" zener >>> centered around the rather large junction area necessary to carry some >>> decent current; the junction of an RF transistor ought to be at least >>> an order of magnitude (several??) smaller than that. >>> >>> Thoughts? >>> >>> Jim >> Well, all of the bipolar transistors seem to have the_specification_ >>of a max reverse VBE of 5 volts, but in fact they all zener in the 8 >>volt region. > >Lots of NPNs zener around 5 volts. If you use the collector and >emitter, you get a "reference zener", a zener in series with a >forware-biased diode, around 6.2 volts with a very low TC. > >For some reason, PNP transistors sometines have higher zener voltages, >10-12 volts maybe. > >John "For some reason"? Try doping levels. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Help save the environment! Please dispose of socialism responsibly!
From: Phil Hobbs on 29 Dec 2009 16:57 On 12/29/2009 12:40 PM, John Larkin wrote: > On Tue, 29 Dec 2009 02:59:51 -0500, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >> On 12/29/2009 12:07 AM, Tim Wescott wrote: >>> On Mon, 28 Dec 2009 19:08:29 -0500, Phil Hobbs wrote: >>> >>>> On 12/28/2009 6:59 PM, Tim Wescott wrote: >>>>> On Mon, 28 Dec 2009 14:49:06 -0800, RST Engineering wrote: >>>>> >>>>>> On Mon, 28 Dec 2009 16:07:24 -0600, Tim Wescott<tim(a)seemywebsite.com> >>>>>> wrote: >>>>>> >>>>>>> On Mon, 28 Dec 2009 13:49:05 -0800, RST Engineering wrote: >>>>>> >>>>>> >>>>>>> It'll be good to know what your results are. >>>>>>> >>>>>>> Twenty years ago you could buy a noise diode from MA-COM (IIRC; it >>>>>>> may have been some other company), home-brew your own circuit to hold >>>>>>> it, then send it back to MA-COM for calibration. I don't know if you >>>>>>> still can. >>>>>>> >>>>>>> A noise diode was, of course, 'just a zener', optimized for use at >>>>>>> microwave frequencies. >>>>>> >>>>>> Noisecom and Micronetics are the only two I know of. Noisecom used to >>>>>> sell "factory seconds" to hams for pennies on the dollar but that >>>>>> practice seems to have gone by the wayside. They, as you noted, would >>>>>> also do a calibration of your design for a few bucks. Gone also. >>>>>> >>>>>> It will be fun to get back to experimenting with something where I >>>>>> don't have a real good idea what the answer is going to be. >>>>>> >>>>>> Jim >>>>> >>>>> I think it's Noisecom that I was thinking of. Dang; I should have >>>>> taken advantage while I could. >>>>> >>>>> I have thought that if you were building something low-noise enough you >>>>> could measure the noise figure with a pair of transmission lines >>>>> terminated in resistors: drop one into ice water (or dry-ice/acetone, >>>>> or LN2), and heat the other one up (boiling water, or a >>>>> not-quite-melted- solder heat furnace). Then switch between them. >>>>> With no current flowing through the resistors, you'd certainly know >>>>> their noise temperatures! >>>>> >>>>> >>>> A common approach in physics labs is to terminate the input with a 300 >>>> kelvin resistor, measure the noise, dunk the resistor in liquid >>>> nitrogen, and measure it again. Works great. >>>> >>> Goodness you keep the heat turned up -- or is that in the summer? >>> >>> It's about 293K in here now, because I can get comfort cheaper with a >>> sweater than by turning up the heat. >>> >> >> Nope, we reduce waste by keeping the house about 59 F in the winter (55 >> at night). So since it's 3 AM here, I'll see your 293 and raise you -8 >> kelvins. ;) > > That sort of frugality would get me divorced. You've met Mo and > probably noticed her unfavorable mass/surface area ratio. > Unfavourable for climate control purposes, anyway. Great for beach purposes. > Car seat warmers are another great marriage-saving invention. > Never did like them. > All of which explains this week's automation project. > Gotcha. My son Simon is going to make some dough by insulating the attic. I wanted to use vermiculite but you basically can't get it any more--which is a pity. You have to use a bit more, but you don't wind up with red eyes and itchy skin the way you do with rock wool or fibreglass. I'm a warm-blooded sort of cove, actually--I nearly melted down in Costa Rica a couple of weeks ago. Cheers Phil Hobbs "There is no bad weather, there are only wrong clothes." -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: Jim Thompson on 29 Dec 2009 17:12 On Tue, 29 Dec 2009 16:57:23 -0500, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: [snip] > >.... My son Simon is going to make some dough by insulating the >attic. I wanted to use vermiculite but you basically can't get it any >more--which is a pity. [snip] That IS a shame. Best insulated house I ever owned had vermiculite filled walls. Only problem was if I cut a hole to add, for instance, another electrical outlet... it poured out on the floor. So I'd catch it in a bucket, do my wire pulling, put the box in place, and seal it. Then go up in the attic and re-pour the vermiculite ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Help save the environment! Please dispose of socialism responsibly!
From: whit3rd on 29 Dec 2009 17:37 On Dec 28, 1:49 pm, RST Engineering <jwei...(a)gmail.com> wrote: > . > . > There was a general discussion in this NG a couple of weeks ago about > using a lightly-biased zener as a noise source. There was no clear > definition about how flat or to what frequency the noise was useful. Avalanche breakdown results in amplification of shot noise. A true 'Zener' (like Claude Zener described) diode is a good approximation of low-voltage breakdown (under 5V) and doesn't have that amplification effect. So, better noise production will occur with higher voltage diodes (I'd try 20V or so), than with a B-E breakdown. The B-E area of any suitable transistor will be large, and limit your high frequency output due to capacitance; maybe a small-signal junction diode will do better. Best, actually, might be a Ne lamp (same avalanche breakdown, very low shunt capacitance), but that'll take some high voltage to strike, and has magnetic field sensitivity. I've seen microwave noise sources that had a discharge lamp inside a waveguide. Point-contact diodes or Schottky will have age degradation issues, because the junction is near the surface. Probably. They aren't really tested or specified for that kind of bias, so you can't assume the right precautions are in place (field rings, surface passivation) to stabilize operation in this reverse-conduction condition.
From: krw on 29 Dec 2009 18:40
On Tue, 29 Dec 2009 05:23:02 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Phil Hobbs" <pcdhSpamMeSenseless(a)electrooptical.net> wrote in message >news:4B39B6F7.1050504(a)electrooptical.net... >> Nope, we reduce waste by keeping the house about 59 F in the winter (55 at >> night). So since it's 3 AM here, I'll see your 293 and raise you -8 >> kelvins. ;) > >Geesh! I try falling asleep at home without a space heater and wake up all >sore, apparently from shivering all night. Has to be at least 68F in here >to be comfortble, I'd guess. Wow! When we lived in VT we had the set-back thermostat set to 59F at night and 64F during the day, with a spike to 68F early morning (with weekends having a different definition of "early"). At night we'd boost it up when we got too cold. Now we keep it at a pretty constant 67F. The heat pump doesn't like being set back. The recovery time sucks. >'Course, at school I'm spoiled, because the hot water radiators are always >cooking at a toasty 72 or so. That's too warm for the winter. |