opamp clamp

I just picked the LT1124 because I use them sometimes and the model was there in LT Spice, so I knew about what it behaves like. In real life, I plan to use an LF353, which is a lot slower. BCX70 and 71 for the transistors. Should be bog stable. I wouldn't normally bother to simulate something this simple.

John

[snip]

For some reason I couldn't find the LT1124 in my copy of LTspice, but I found it on Linear's website.

One needs to express caution, bog slow doesn't necessarily equate with bog stable.

My biggest scare was recent. An amplifier that PSpice said has serious ringing/near oscillation and my LoopGain tool couldn't cope with the multiple feed back loops (Auggie Ochoa and I presently working a solution), came out of chip processing working just ducky.

In case you haven't noticed, I tend toward overly cautious ;-)

...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     |
             
         America: Land of the Free, Because of the Brave

Sure, but the emitter followers have voltage gains below 1, and the amp is unity-gain stable, so it's pretty simple. The only gotcha is possible VHF oscillations in the transistors themselves, but the resistive voltage divider thing in the base kills that.

Well, you can't change parts, or cut-and-jumper, if things get grim. I can. I also leave hooks (unpopulated caps, zero-ohm jumpers, alternate loop compensations) when I have a funny feeling about things, so we can move on and build boards without first analyzing everything to death. Besides which, I'm chairman of the board and I'm unlikely to fire myself.

John

[snip]

Sno-o-o-ort ;-)

Actually, in the I/C world, we do leave spare parts wherever there's space.

And we do FIB (focused ion beam) patches, cutting "wires" and making other connections to debug problem areas.

The aforementioned chip, where ALL of my stuff works ;-) the ESD designer blew it and created a sneak path between the +2.5V and +1.8V supplies, so we FIB'd it to find how it was happening.

...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     |
             
         America: Land of the Free, Because of the Brave

Yeah, but which one are you going with?

Which clamp? The 3-resistor, dual emitter-follower thing. If I make the +5 and -5 supplies accurate and more important make them track, I can clamp a few tenths of a volt inside +5 and ground, enough to guarantee that downstream single-supply stuff won't get railed.

John

Then, logically, since I'm happy, everybody is happy.

John

I'm happy, too ;-)

...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 | |

| 1962 | America: Land of the Free, Because of the Brave

Do you design chips such that a maximum number of interconnects are FIBable, to leave more latitude for patching?

John

Mostly it's arranged such that "cells" (individual functions) can be detached and tested individually.

When it's a more leisurely pace we often create test metal masks to allow separated functional testing.

In this particular case a test mux was built-in to do that, but the ESD fart munged that up :-(

...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     |
             
         America: Land of the Free, Because of the Brave

I'm not happy. George W Bush is still the 'decider' for all of us, making lots of *bad* decisions.

I suppose you'd rather have Al Gore ?:-)

...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     |
             
         America: Land of the Free, Because of the Brave

He decides virtually nothing about my life. And last time I looked, Congress passed the laws and the Courts reviewed and enforced them.

Congress is even less popular now than W.

Is the occupant of the White House so influential that he/she controls your happiness?

John

You are happy with him running the country, I am not.

Makes me happy too.

Everyone makes *bad* decisions. That's what makes hindsight so cool.

--
Keith

He doesn't run my life. Only I do that.

John

--
Geez, John, It must be wonderful to be able to be so above it all
that something like the assassination of Benazir Bhutto doesn\'t
alter your state of blissful self-indulgence.

--
Hmm... You\'re above the law and the IRS doesn\'t exact their toll on
you?

What a convenient fantasy!

Roughly 200,000 people die every day, and both you and I will die one of these days, too. You can let that reality ruin the few days you are blessed with, or you can appreciate your body and this planet. It's your choice.

And if you sometimes feel bad about people suffering and dying, donate heavily to Doctors Without Borders and girls's schools in Africa and family homeless shelters, like we do, instead of reading newspaper headlines and clucking.

John