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Old 27th August 2012, 01:58 PM   #321
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Quote:
Originally Posted by john curl View Post
No, please do NOT use those devices: Use J113, J175 devices.
OK, I need to dig up the Spice models of the J113/J175. Meanwhile, I plugged in the J310/J271 instead as the output stage of the venerable Melcor 1731, and it doesn't look terribly bad for 6+2 actives: GBW of ~3 MHz. Degeneration can be added, LTP compensation changed, etc., to improve this.
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Old 27th August 2012, 02:09 PM   #322
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Originally Posted by linuxguru View Post
OK, I need to dig up the Spice models of the J113/J175. Meanwhile, I plugged in the J310/J271 instead as the output stage of the venerable Melcor 1731, and it doesn't look terribly bad for 6+2 actives: GBW of ~3 MHz. Degeneration can be added, LTP compensation changed, etc., to improve this.
I was wondering when someone was going to grab one of the professional discrete opamps. API2520 anyone? DOA-12, DOA-17 from Five Fish... etc.

Maybe we should make it fit the pro plugin format of 1.1" square?
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Old 27th August 2012, 02:14 PM   #323
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Originally Posted by dirkwright View Post
Too much yapping about dies and other things and not enough modeling!
2mv untrimmed...wait till you start finding thermal response issues in the 10 to 100 millisecond realm..then you'll come crying to the die people. Plastic just doesn't have a high diffusion velocity...

jn
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Old 27th August 2012, 02:18 PM   #324
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Originally Posted by jneutron View Post
2mv untrimmed...wait till you start finding thermal response issues in the 10 to 100 millisecond realm..then you'll come crying to the die people. Plastic just doesn't have a high diffusion velocity...

jn
Fortunately for me, I don't know what this means!

(except that it sounds bad)
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Old 27th August 2012, 02:37 PM   #325
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Originally Posted by dirkwright View Post
Fortunately for me, I don't know what this means!

(except that it sounds bad)
Da#n..I was sipping coffee...

As a die pulls current, it heats up a bit. The best thing would be for both die to be thermally in contact with each other to minimize the change of one vs the other. I recall somebody actually epoxying a temp monitor to the top surface of some power chips to do this, though I don't like that...

Thermally, it takes about 100 uSec to 10 milliseconds for the thermal wave to make it to the substrate a die is attached to, under that time frame no external parts can sense a temp rise directly to comp the circuit.

The LM 194 transistor pair was the ultimate in this regard, as it had two pairs of transistors, cross connected on the chip. This prevented thermal gradients from affecting the performance, made for some good matching.

jn
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Old 27th August 2012, 02:45 PM   #326
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My work back in the day was with mil spec hybrids, so laser scribing was a definite no-no...we had to pass PIND testing.

jn
Have you seen the femto-second laser cutting? Too fast for the phonons.
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Old 27th August 2012, 02:54 PM   #327
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Quote:
Originally Posted by jneutron View Post
Da#n..I was sipping coffee...

As a die pulls current, it heats up a bit. The best thing would be for both die to be thermally in contact with each other to minimize the change of one vs the other. I recall somebody actually epoxying a temp monitor to the top surface of some power chips to do this, though I don't like that...

Thermally, it takes about 100 uSec to 10 milliseconds for the thermal wave to make it to the substrate a die is attached to, under that time frame no external parts can sense a temp rise directly to comp the circuit.

The LM 194 transistor pair was the ultimate in this regard, as it had two pairs of transistors, cross connected on the chip. This prevented thermal gradients from affecting the performance, made for some good matching.

jn
HAHA.

OK, but I don't think they make power transistors like this, do they?

I would assume that the input differential pairs would be monolithic if possible. For example, I know that I can get current mirrors (SMD) that are in one unit with 3 really tiny tabs. I do know that PNP and NPN transistor pairs are available as one unit also, but I do not know if jeft's are available like that any more. So, maybe have to change the circuit to bipolar inputs in order to take advantage of monolithic construction and stability? somebody? anybody?

I'm virtually certain that the two DOA's from Five Fish use monolithic transistor pairs at the input stage. I'm just not sure about getting complementary sets (I mean an NPN monolithic pair that are a complement to another PNP monolithic pair).

I've posted this link before and got no responses.
Linear Integrated Systems - Products
They make monolithic transistor pairs but they don't say if they are complementary sets.

If not, then the topology for the DOA has to be changed.
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Old 27th August 2012, 03:09 PM   #328
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Default Bryston DOA

Bryston, similar to GAS
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Old 27th August 2012, 03:17 PM   #329
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Originally Posted by dirkwright View Post
HAHA.

OK, but I don't think they make power transistors like this, do they?
I don't think so. Gluing a comp chip on top, yes.

Using chips on board would be thermally the fastest, it just requires bonding the wires to the copper traces. Many manu's currently do it, then glob top them. The tech is pretty good now, so it's rather reliable.

It'd be great to find a house out there willing to do small scale proto's using a design created in this thread..

It also allows pre-matching of any device type for use on the front end.. And man, the component density increase would allow major circuits on the same real estate over smt.

jn

Last edited by jneutron; 27th August 2012 at 03:21 PM.
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Old 27th August 2012, 03:26 PM   #330
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The JLH design in #306 is an interesting and useful design, both to talk about, and to upgrade to newer devices.
The original parts made by Motorola were available since the very late '60's and were the FIRST 'complementary' pair easily available. I used them for complementary jfet followers in 1970, and within a year developed the complementary differential jfet input stage with them. However, by 1972, Siliconix came out with better, higher Gm devices that appear today as the J113 and J175, derived from the NC and PS geometry that they developed. Unfortunately, due to mobility differences between the N and P channel material, the N channel jfets had about twice the Gm as the P channel.
Later, much later, when Toshiba introduced its line of complementary fets, they compensated for this by making the P channel larger to get a better Gm match, losing parasitic capacitance similarity, unfortunately, but a better overall combination, that we have run with for about 1/3 century, and now we are losing out.
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