Adjustable current mirror

I'm considering those versus Kikusui at the moment. Any comments, John?

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)

Great stuff. Jim's dad played in a Bluegrass band but not sure if any of their pieces are online for lisnin' in. We only have one small local station that plays Bluegrass once in a while but luckily there's plenty of web streams.

--
Regards, Joerg

http://www.analogconsultants.com/

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I grew up on this...

Every Saturday night on local TV station WSAZ, LIVE ;-)

And I used to be able to get this on AM radio even when I was in Cambridge going to school...

...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     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Do you mean something like this?

Nice piece and the cool look on the face of the banjo player in contrast to the music is hilarious!

But currently I'm more a fan of classical English folk songs, as in my latest piano performance:

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de

=20

like=20

roughly=20

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a=20

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so Xc =3D=20

small=20

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plus=20

I would be wondering what the DCR would mount up to. If that gets too = high=20 even a 600 mV source would not get to a dozen pA.

Magnetization=20

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I had suggested a 2 x 2 mm core, which implies the average diameter is a 4mm square, or 16mm circumference. 4e6 turns at 16mm is 640Mmm = 640km. Copper is 17nohm*m or 1.74 x 10^15 ohms. Hmm, that seems unbelievably high.

If it remains 64MH over a suitable range of frequencies, it will have Q = 1 at 4.3MHz. That's definitely not going to happen!

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Hmm ... sez "on air now" Rush Limbaugh :-)

--
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

Alright, my kind of music!

Very nice. You also have a pretty good keyboard there.

I just tuned our old piano but one of the B2 tuning pins is slipping. Darn, now I have to find time to take the strings out and do the old sandpaper trick, hoping the strings won't snap ...

--
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

Thanks. The keyboard is good, but I'm using it as a MIDI keyboard, only and a soft synthesizer on PC (Pianoteq). But I'm still searching for the perfect sound. Currently there is no software available which sounds and feels like an acoustic piano, or at least I don't know it.

Take care, the tension of the strings can be high.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de

Also saw a quad (MMPQ3904). Are these thermally coupled in any special way, or are they just dies stuck together with epoxy?

Is the cost of a dual or quad array (and the chance of it not working with my chincy PCB drawing skills) justified over, say, gluing a few TO-92's together?

Tim

When I was a student (1958-1962) it was strictly a hillbilly station. ...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     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Here's one for real purists:

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Most of the duals/quads are separate chips in one package. The thermal coupling is atrocious, not much better than separate parts.

John

For currents 'up to 5 mA' and 0.5V collector bias, the thermal coupling doesn't have to deal with a lot of self-heating. It' only has to be good against temperature gradients in the printed wiring board, and breezes. Surface mount parts MIGHT match better if the PCB were slotted to make thermal breaks.

Logarithm converters are commonly seen with TO-92 discretes in a chunk of metal to keep T matched. Aluminum block, heatsink goo, Teflon standoffs for the sensitive points... buying a quad is certainly less ugly.

I did some tests on a UPA800, a tiny 2-chip RF dual. Differential theta was ballpark 120 K/W. So your 2.5 mW will cause a temperature imbalance of about 0.3K, which is an offset of around 750 microvolts.

John

Yeah, but remember it's a 0.1-to-10 multiple of 5mA, or potentially up to

50mA (although I may limit that to 5-20mA for practical reasons). The

The THAT300 quad transistors are on a silicon die, isolated by oxide; that makes them closer and connected by high-thermal-conductivity silicon, compared to multichip versions. Spec sheet doesn't have a real number, though.

This

ftp://jjlarkin.lmi.net/UPA800_Slow_Xtalk_500uv.JPG

is the Vbe drop of one transistor, as the other is pulsed at 80 milliwatts. Vertical scale is 500 uV/div. Interesting thermal transient.

John

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The duration of the downslope is indicative of a transient temperature change due to hot-transistor heating cold-transistor; that's the duration of significant temperature difference between the two. The longer upslope, while the heat bleeds out the heatsink, occurs with transistor temperatures at/near match, so isn't indicative of any error in circuit outputs.

If the transistors are in square array, for a mirror gain of 1, you can put the unknown-input and output transistors diagonally opposite, and their matched heat output means the balance is maintained. When the mirror gain is at an extreme, the current imbalance will generate some error... especially the highest heat production, which is the output transistor at high input with high gain. It might be worth servo-ing a cascode transistor to get the output voltage burden to 0.3V.