Why are you guys discussing electronics in a political discussion group?
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7 years ago
-- Rick C
current limiter thingie
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7 years ago
Sure. Jfets enhance a bit as the gate goes in the conducting direction, positive in an n-fet. It's not huge. Phemts, with higher transconductance, can enhance well over 2:1.
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-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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7 years ago
Its really the Vpinhoff/Vtho bit that does the damage. There are two main parameters, a W/L (gm) factor, and the pinchoff. Pinchoff varies all over the place. gm factor not so much.
-- Kevin Aylward
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- SuperSpice
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7 years ago
Can't say I'm overally keen on that technique. For low voltages, its a floating gate. Not wonderful for noise pickup. HF Feedthrough upsetting it not that great either.
As I know you are well aware, its electrically better to switch the gate to the relevant terminal, dependant on the input polarity. A tad more circuitry though...
-- Kevin Aylward
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- SuperSpice
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7 years ago
Indeed.
-- Kevin Aylward
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- SuperSpice
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7 years ago
We need to make those jfets great again.
-- John Devereux
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7 years ago
It was a demo for current-limiting.
Sure >:-}
Of course. The demo was for the paisan-level... they'd gag and throw-up if I showed a full-fledged protection scheme for an unpowered bus driver (bus signal voltages larger than local VDD).
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.
"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie
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7 years ago
It's a welcome change. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.
"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie
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7 years ago
Odd, that you'd call high capacitance 'terrible'. High capacitance makes them good for a parametric amplifier input. Horses for courses.
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7 years ago
[snip]
Actually the typical protection case would switch the _body_ (P-channel MOS device)... the gate would a separate control mechanism... tri-state, whatever. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.
"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie
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7 years ago
In my business, 1 pF is a lot of capacitance.
I'd think the high series resistance of a jfet diode would be bad news for RF. Have you used a jfet as a parametric amp? Why not use a real varicap?
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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7 years ago
Ah, define 'real'. Capacitance versus voltage IS real for Zener diodes, JFETs, varicaps, photodiodes, etc. Low-input-current parametric amps aren't really the target for varicap duals, the varicap specs for leakage and capacitance near zero-voltage bias are ... sparse to empty.
Not sure about series resistance of "a jfet diode", either. Balancing inputs, how does that enter into figure-of-merit?