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From: maitre Aliboron on 20 Apr 2006 12:39
Any idea for a voltage controlled current source
(linear of course) to be implemented in a CMOS
process? The difficult part is to get rid of process
variations (the most dispersed component seems to
be the poly resistor)

Variants from standard textbook bias sources
(Vittoz, PTAT, Wilson...) seem not to work properly;
I get changes of more than +/- 40% from centered value.
Temperature compensation is not important, nor PSRR.

I'm looking for solutions which compensate
resistors variations, for example making use of
a differential pair. I could make use of a bandgap,
if necessary, though I prefer to avoid it.
Do you know any solution?

thanks.

maitre Aliboron


From: Jim Thompson on 20 Apr 2006 13:08
On Thu, 20 Apr 2006 18:39:25 +0200, "maitre Aliboron"
<aliboron(a)despammed.com> wrote:

>Any idea for a voltage controlled current source
>(linear of course) to be implemented in a CMOS
>process? The difficult part is to get rid of process
>variations (the most dispersed component seems to
>be the poly resistor)
>
>Variants from standard textbook bias sources
>(Vittoz, PTAT, Wilson...) seem not to work properly;
>I get changes of more than +/- 40% from centered value.
>Temperature compensation is not important, nor PSRR.
>
>I'm looking for solutions which compensate
>resistors variations, for example making use of
>a differential pair. I could make use of a bandgap,
>if necessary, though I prefer to avoid it.
>Do you know any solution?
>
>thanks.
>
>maitre Aliboron
>

Use an external accurate resistor ?:-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

Old Latin teachers never die...they just decline
From: maitre Aliboron on 20 Apr 2006 13:15
> Use an external accurate resistor ?:-)

impossible... :-))

For the moment I'm oriented toward something weird and
not usual like CCII, differential transconductors or very nice
stuff like that... But I guess I can find something simpler, (I
highly hope).


--
maitre Aliboron


From: Frank Miles on 20 Apr 2006 13:27
In article <e28dfu$ce6$1(a)newsreader.mailgate.org>,
maitre Aliboron <aliboron(a)despammed.com> wrote:
>Any idea for a voltage controlled current source
>(linear of course) to be implemented in a CMOS
>process? The difficult part is to get rid of process
>variations (the most dispersed component seems to
>be the poly resistor)
>
>Variants from standard textbook bias sources
>(Vittoz, PTAT, Wilson...) seem not to work properly;
>I get changes of more than +/- 40% from centered value.
>Temperature compensation is not important, nor PSRR.
>
>I'm looking for solutions which compensate
>resistors variations, for example making use of
>a differential pair. I could make use of a bandgap,
>if necessary, though I prefer to avoid it.
>Do you know any solution?
>
>thanks.
>
>maitre Aliboron

Does it all have to be on-chip?
Can you make accurate capacitors?

-f
--
From: Jim Thompson on 20 Apr 2006 13:34
On Thu, 20 Apr 2006 19:15:29 +0200, "maitre Aliboron"
<aliboron(a)despammed.com> wrote:

>> Use an external accurate resistor ?:-)
>
>impossible... :-))
>
>For the moment I'm oriented toward something weird and
>not usual like CCII, differential transconductors or very nice
>stuff like that... But I guess I can find something simpler, (I
>highly hope).

How can you make an accurate absolute value?

I _have_ done systems that periodically re-calibrate themselves, but
you have to feed it a reference during the re-calibration.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

Old Latin teachers never die...they just decline
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