steps
reliably=20
while=20
=46or fully continuous i would look at a application of a Gilbert cell = multiplier. =20 There are some relatively exposed Gilbert cell ICs available.
=46or a steppy solution an 8 or more bit (multiplying) current diverting = DAC. Though i am not sure if a DAC will work well over two decades of = reference=20 current, you may have to subrange to two or three steps (that may = overlap).
Both solutions will require some appropriate scaling before or after or = both.
...
-V'
or=20
plifer.gif
are on=20
I doubt if i still have the schematic. I should be able to do a fresh=20 instance with current parts. In a couple of days as an LTspice file OK. The parts to the original may be unobtainium now.
Hmm. I have some MC1496's laying around, that's halfway there. Or use a TIA. I wouldn't need four quadrants, one would be enough. That would even suggest a JFET. The problem is making the 0.1 to 10 ratio repeatable with an output from 50nA to 50mA (maybe not 50 on the highest range, I could settle for 5mA max.). That means putting the programming current into the tail is tricky (a regular current mirror would do okay), and the output can only be varied from 1 to 0.01 instead of 0.1 to 10 times (well, close enough).
In this circuit,
Thanks, this is something to think about.
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
That circuit is so astoundingly bad that it's worth saving.
John
Bad for what?
It has an unusually wide range, as discrete circuits go. On 680pF, I got from 1Hz to 4.5MHz in a single range. Six decades isn't bad for a 2N440x. Smaller RF BJT's would go lower, or you could do range switching or more exotic approaches (leaky photodiode?).
Besides the wide range, what impressed me is the diffamp got the 2N4403 switching in about 20ns, for a balls-out maximum frequency around 35MHz. Faster transistors would also take this arbitrarily high (the PHEMTs you're so fond of would probably make a proper RC oscillator in the GHz). Say, do they even make P type stupidfast transistors, SiGe or otherwise? I remember they don't bother with P type GaAs or InP since they suck for holes.
I don't remember if, when set at ~10Hz or so, the frequency drifted by a decade or so when I touched the leftmost transistor. It ought to. I do remember seeing it change in steps, since I was using a wirewound pot.
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
Certainly worth saving. You might learn something from those of us who can _really_ design at the device level, instead of copying from... ;-) ...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.
Let's see how many people can each find one problem.
The most obvious one is the the charge/discharge currents depend on the betas of the upper and lower mirror transistors. That's probably why there are two PNPs and three NPNs: they were selected to work.
John
Well, the duty cycle ended up fairly close to 50% just picking random 440x's out of the box. No selection, put it together and it worked. Why, were you expecting 3 PNP's and 2 NPNs if they were selected?
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
? The top mirror gives +I, the bottom mirror gives -2*I, where I is the current through the NPN emitter follower.
When the 2N4403 (emitter connected to +8) is "on" you get +I (cause it conducts the -2I away through the diode), when it is off you get a net of -I.
I got a crap mark in Uni for a circuit much like this one, because the TA didn't understand it. 8-(
There are sufficient "errors" in there to suppose drafting goofs. ...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.
If you select the transistors carefully, or get lucky.
Putting two or three or seventeen transistors in parallel in a circuit like this doesn't scale the mirror ratios, it just sort of half-assed averages out the betas. If there is a 2:1 ratio, it's because the NPNs have an average beta twice that of the PNPs.
A 2N4403 has a min specified beta of 60 at 1 mA, typ about 250, no specified max.
Or because he did?
Next problem?
John
Hoo Haa! Keep the BS coming, I'm keeping score ;-)
It's not nearly as bad as my first glance suggested.
Snot-nosed comment. Probably voted for Obama ;-)
...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.
John Larkin's statement there is SO-DUMBASSED as to warrant special mention ;-) Keep note of that!
The only thing that stands out as defective in the schematic is that the placement of the two 1N914's is wrong to accomplish the desired up/down current steering.
I was using such a saw-tooth scheme (with substantial improvement :-)
30+ years ago in GenRad switchers, which continue to work just fine to this day (built around LM339's). ...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.
Oops, misread the mirror connections. It's not a great mirror setup, but it's not seriously beta dependent.
Plenty of other issues, though.
John
Jim Thompson a écrit :
??? Not even, but the schmidt trigger has wrong feedback (take it from the other 3904 collector). And the 100p miller cap is not only unnecessary but worsens the PSRR without any benefit.
It seems your silicon has one unnecessary pass.
-- Thanks, Fred.
Yep, the real defect is the Schmitt. Swapping phase still doesn't fix it. I can't figure out what was the intent of whoever designed this.
Have no idea why people spray capacitors around ;-)
My "silicon"? Those GenRad supplies used everything off-the-shelf. ...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.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
Breadboard, duh ?-)
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
Indeed! Then the 4.7k positive feedback is actually positive.
That's ONE error. Come on, can't you so-called professionals do better than this? ;-D
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
Hmmm, look harder...
I meant that "virtual one" when you said: >>> The only thing that stands out as defective in the schematic is that >>> the placement of the two 1N914's is wrong to accomplish the desired >>> up/down current steering.
-- Thanks, Fred.
The mirrors are just fine (for a hacker circuit), but I had to patch up the Schmitt...
In general, the operating currents are way too high. ...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.
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