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No, I'd be willing to bet the sound card is way too noisy to be useful as a source at these levels. The diode bias supply has only a few nV/ rt Hz of noise. The sound card would be useful as the detector/ FFT analyzer.
George H.
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Yeah, I first thought it was some excess noise in the diode, but then noticed that to BW was dropping at the higher currents... as you say, more noise gain. With a lower voltage noise opamp I could have extended the linear range.
Say is that why even a low voltage zener would be a better noise source? (The dynamic impedance is higher.) What is the dynamic impedance of a zener?
George H.
My preference for noise sources is shot noise or thermal noise. Zeners have weird behaviour, and anything involving avalanches is liable to be destructive, and so change that behaviour over time.
To use forward conduction shot noise, I'd probably use a diode-connected transistor with the cathode grounded, followed by a noninverting amp. To be fancy, one could use a dual diode such as a BAV99K, like this. That gets you sqrt(2) times the noise and gets rid of most of the DC offset. A MAT14 with two diode-connected transistors per side would get you twice the noise and pretty well get rid of the DC drift as well.
Cheers
Phil Hobbs
OP27 or something VCC |\
0--RRRR------*----------------------|+\ | | >----------*---0 | GND *-|-/ | | | | |/ | | | | | | | | | | | *-----R2R2------* | | | | | R --- --- 1 BAV99K \ / \ / R V V 1 --- --- | | | | *------------* GND | | | R/2 R/2 R/2 R/2 | | VEE | 0------------*-- 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 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
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The right sort of scrambler could increase the run length.
John
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With 10k ohm input impedance, it's already got a heavy hit against it for nV/rtHz
Yeah just put one of those 1nV/rtHz Linear parts in front of it with a gain of 100 and the soundcard is waaaaay below
The transistor will produce much more noise than the zener. Manufacturers have worked to reduce the noise from the zener, not so for the transistor. The MPSH-10 costs 12 cents in one-offs from futurelec
-- Using Opera's revolutionary email client: http://www.opera.com/mail/
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Oh more 'fancy' tricks, with diodes. But I'm hip to that now.
How much noise can you get out of this? Let's just stick to the single diode with cathode grounded.
I crunched a few numbers and got less than I would from just a resistor.... (Say I run 100uA through it, current noise is sqrt(2*e*I) =3D
5.6e**-12 x Rdiode (250 ohms) ~ 1.4nV/rtHz.... Not worth the trouble. (Unless I made some silly mistake.)George H.
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Although # 2 probaly makes a fair white noise generator all by it's self :)
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And how do they do that? The semiconductor physics don't give them a lot of options.
Newark offers the ON-Semi MMBZ5223BLT1G 2.7V Zener for 3.5 cents (one- off) in an SOT-23 packages, There are slightly cheaper parts further down the list.
-- Bill Sloman, Nijmegen
Yes, I tried the zener idea. No Go. The amp produced more noise. I will try an RF transistor next.
Have done digital noise gen before, but the parts count was too high for my app.
I do recall one manufacturer producing a dedicated white noise IC, but I understood it is no longer available.
Leo
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What circiut? Something similar to what Phil posted? You might try sticking the zener into a TIA. But I don't think low voltage zeners are going to give much more noise than pn diodes.
I know squat about uP's but why not a pseudo-random bit stream that get's mixed up... Like Tim and others suggested. That seems to me to be lower parts count than any analog method.
George H.
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Any idea how much one of the diodes costs? (I won't ask about the modules)
George H.
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The shot noise voltage on a PN junction looks just like a resistor equal to the junction resistance at a temperature of T_amb/2.
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 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Large junction area (big cap)
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I've use the transistor before - I'd post a circuit but considering the trouble I am having with another circuit... Depending on the frequency and resolution you need an 8 pin micro might work. I got 20kHz+ from an 12F683 running at 20MHz and using 5 binary weighted resistors as a DAC.
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It's not that big. As I mentioned, this would only be a factor if you wanted very high frequency noise, which the OP doesn't seem to need.
-- Bill Sloman, Nijmegen
I seem to racall pricing starting at $10 or some such, much more for deep microwave stuff.
They do have some parts that make nice noise at low currents. Tiny junctions maybe? I'd suspect that a microwave transistor b-e junction might be similar.
Somebody with time could research zener noise versus voltage, junction area, stuff like that.
John
The use of avalanche in gas tubes (where the ions can erode the terminals) has some aging issues, but Zener breakdown, if the diode is a 'buried' type (without surface-of-die lateral currents) one wouldn't need to worry much about aging at low current. The more significant problem is in selecting devices that haven't got significant mode-hopping current fluctuations (some zeners at low current have multiple quasistable states). That, I presume, is what you're calling 'weird behaviour'. I really like avalanche, because it offers SO MUCH broadband power gain, the rest of the amplification job is greatly simplified.
Don't know what to say. In the experiments I did the transistor junctions were an order of magnitude or more nosier than OTS zener diodes
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