| Author |
Message |
John B
Guest
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 Posted:
Thu Dec 08, 2005 5:35 pm Post subject:
Re: adding an enable to a bipolar op-amp, how??? |
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On 07/12/2005 the venerable Hank etched in runes:
| Quote: | Hi,
I am converting the 0 to 4.096V output of a DAC into -2.048V to
+2.048V using an op-amp as a differential amplifier. On powerup, the
DAC is reset to 0V, which obviously makes the output of the op-amp
-2.048V. I want the output of the op-amp to be 0V on powerup until I
enable it with 5V logic.
Is there a really easy way of implementing this that I am just
missing? All of my solutions seem too complicated for such a
seemingly simple requirement. :-(
Thanks,
Hank
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Use a CA3130 op-amp. It has an output enable pin.
--
John B
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Tony Williams
Guest
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| Posted:
Fri Dec 09, 2005 10:54 am Post subject:
Re: adding an enable to a bipolar op-amp, how??? |
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In article <4dd5ed9a31tonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@ledelec.demon.co.uk> wrote:
| Quote: | Switch 2R R
4.096Vref -+----+/+------/\/\---+---/\/\--+--> Vout
| _ |
+--|- \ |
|Op >--+
+--|+_/
|
DAC(at 0V) +------------/\/\----+---/\/\--+0V
R 2R |
~ ~~
Quietly correcting a drawing typo before anyone
else notices and comments.
--
Tony Williams. |
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Fred Bloggs
Guest
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| Posted:
Fri Dec 09, 2005 5:35 pm Post subject:
Re: adding an enable to a bipolar op-amp, how??? |
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Tony Williams wrote:
| Quote: | In article <4398268A.6010003@nospam.com>,
Fred Bloggs <nospam@nospam.com> wrote:
.
. +5
. |
. |
. 4.096V >--[R3]-+-[R4]------|----.
. | | |
. | | OA |
. '---------|-\ |
. | >---+-> Out
. .---------|+/
. | |
. Vin >--[R1]-+-[R2]------+--- 0v.
[snip]
A caveat Fred. A 'RRIO' opamp whose o/p stage is a
bipolar transistor with a parallel c-c FET for the final
pulldown will get it's Vout lifted by the current through
R3+R4. The '324-type is quite an ambush for this effect
when running on single rail. Must use an opamp with a
genuine CMOS o/p stage.
|
Right- well anyone who would use an LM324 for a 12-bit system would
deserve it- maybe something like even a LT1013 would be good- and this
will sink the feedforward bias. Then U04 type for the pulldown gate on
V- with a Miller cap to make the transition without too much disruption.
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Jim Thompson
Guest
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| Posted:
Fri Dec 09, 2005 5:35 pm Post subject:
Re: adding an enable to a bipolar op-amp, how??? |
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On Fri, 09 Dec 2005 10:54:29 +0000 (GMT), Tony Williams
<tonyw@ledelec.demon.co.uk> wrote:
| Quote: | In article <4dd5ed9a31tonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@ledelec.demon.co.uk> wrote:
Switch 2R R
4.096Vref -+----+/+------/\/\---+---/\/\--+--> Vout
| _ |
+--|- \ |
|Op >--+
+--|+_/
|
DAC(at 0V) +------------/\/\----+---/\/\--+0V
R 2R
~ ~~
Quietly correcting a drawing typo before anyone
else notices and comments.
|
I noticed, but didn't think it needed comment ;-)
...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 |
I love to cook with wine. Sometimes I even put it in the food. |
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