I'm familiar with the techniques for linearizing a JFET for audio attentuator/compression applications.
Does anyone know of a similar approach using MOSFET's ??
...Jim Thompson
-- | James E.Thompson, P.E. | 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
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| 1962 |
If we knew what we were doing, it wouldn't be called research... -- Albert Einstein
A differential pair of MOSFETs has the same sigmoid transfer characteristic as any other diff pair; and if you modulate the source current, the gain goes down. So, the same current mirrors as in (for instance) CA4046, and some suitable cascade of low-gain diff pairs, can do compression. I'd almost prefer to do it with switches and resistors, though: attenuation with resistors is predictable and MOSFETs were born to switch.
I need a MOSFET-based variable resistor that is linear in the first AND third quadrant.
...Jim Thompson
--
| James E.Thompson, P.E. | 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
Cannot help much myself, but figs. 74-78 of the following ENORMOUS pdf (a scanned document) might provide some clues. It's a patent about MOSFET implementation of complete radio receivers, including audio attenuators and AGC.
--
| James E.Thompson, P.E. | 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
Your "2 resistors trick" is spot on. I just pasted two resistors into the simulator (AC-coupled the feedback one so it didn't drop the control voltage), then twiddled the ratio until I had symmetry.
Interesting, it's different from the 1:1 you usually see with a JFET...
I have 190K (feedback) and 1Meg from the control.
One digit asymmetry at the third place to the right of the decimal point!
Thanks for the _push_ ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | 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
p140, except, for a MOSFET, I used 190K for the upper resistor, 1Meg for the resistor from Vcontrol to the gate. I also have a capacitor in series with the 190K.
...Jim Thompson
--
| James E.Thompson, P.E. | 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" a écrit dans le message de news: snipped-for-privacy@4ax.com...
Wow, great!
But I'm somewhat surprised at the resistors ratio. This trick works for a JFET because it has an almost quadratic Id (some that I precisely measured had a 1.85 exponent and required tweaking the resistor ratio, but just a bit). I just mentionned this because I knew (maybe erroneously) that it'd be integrated and you'd have small geometry mosfets (hence they won't work in the subthershold region were they aren't quadratic anymore and they don't have the parasitic diode too). Now the ratio you came to seems to indicate otherwise...
It'd be interesting to know more about the mosfet and its bias/working conditions... Maybe you can post its parameters (but I'm not holding my breath there).
"Jim Thompson" a écrit dans le message de news: snipped-for-privacy@4ax.com...
Wow, great!
But I'm somewhat surprised at the resistors ratio. This trick works for a JFET because it has an almost quadratic Id (some that I precisely measured had a 1.85 exponent and required tweaking the resistor ratio, but just a bit). I just mentionned this because I knew (maybe erroneously) that it'd be integrated and you'd have small geometry mosfets (hence they won't work in the subthershold region were they aren't quadratic anymore and they don't have the parasitic diode too). Now the ratio you came to seems to indicate otherwise...
It'd be interesting to know more about the mosfet and its bias/working conditions... Maybe you can post its parameters (but I'm not holding my breath there).
Must stay resistive at ±2mA current signal drive, decent to ±5mA
As usual I can't say anything about the application right now, maybe in six months, or so.
...Jim Thompson
--
| James E.Thompson, P.E. | 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 |
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