Gated Opamp

You could always stick an analogue switch in there.

Graham

Amusing! You wouldn't happen to be with Raytheon, El Segundo, would you? Ther aren't any MC1445/1545 to be had, but I'd be happy to recreate one for you, on the process of your choice ;-)

...Jim Thompson

On Thu, 14 Jul 2005 23:04:10 -0500, Thomas Dean wroth:

Add a pair of inversly connected (back to back parallel) signal diodes where I've shown "series" and "parll". The ones between the amp and the xducer will conduct during the transmitt pulse and you'll only lose .6 volts. The ones at the rcvr, along with the added resistor will limit the voltage the receiver sees to .6 volts during the transmitt pulse.

After the transmit pulse, the series diodes will disconnect the amp from the transducer because the revceive voltage will be less than .6 volts and the parallel diodes won't conduct either so the rcvr amp gets the signal.

Make the resistor between the transducer and the receive amp equal to the amp's input impedance.

Jim

The MC1445/1545 was a very useful device. I'm surprised that it was obsoleted by Motorola and not picked up by someone.

I note, with considerable amusement (and pride :-), that the first OpAmp I ever designed, MC1530/31 (~1963), is still being manufactured by Lansdale.

...Jim Thompson

The 733 originated, IIRC, from Fairchild.... may have even been a Widlar design before National got started.

...Jim Thompson

ST make the (cheap) 'TSH94' quad opamp. 2 of the amps can be switched on/off, using logic enable pins.

Capping the NF at at least 3dB right off the bat, and ignoring transmission mismatch loss...

Hello Thomas,

Even if there was I would hesitate to design in such a part. It might go obsolete on you down the line. All it takes is a major purchaser to end a legacy product and sales qties dropping below what their executives consider profitable enough. Then you might hear that dreaded clang of the last order bell.

Look at T/R switches. They can be designed around ordinary diodes. If you use Google try the differend spellings such as TR, T/R and T-R. I believe Agilent still has the T/R app notes out there from the old HP times.

Regards, Joerg

Hello Jim,

Probably the market was too small or dried up for some reason. This has often doomed very nice chips such as logamps. They were excellent but the world just didn't need enough tons of them.

Wow, so it is in it's 5th decade. Stuff from my hand that is still in production is only in the 2nd. But in medical most designs do not stay in production too long.

I still have the MC1590 in a round can. IIRC you had your hands in that one, too. And used lots of 733's since they were always an absolute bargain. I always thought the 733 was a Philips design since that's where ours came from but Motorola had them as well.

Regards, Joerg

Hello Jim,

The surprising thing is that National dropped the LM733 while TI still sells the uA733. Must be a good seller since it lists at 34c on their page. That is still one heck of a deal. Considering that the chip is from around 1970 it almost has the legacy of the Corvette.

Regards, Joerg

I've used the Analog Devices AD810 for something close to this. See

-- Regards, Carl Ijames carl.ijames at verizon.net

Hello John,

These look nice. In a transducer application the OP needs to make sure that nothing gets fried though. If the pulse doesn't exceed the rails and the tranducer doesn't ring too badly he may be ok.

Another issue is pulse recovery. In ultrasound that is a big factor, mainly how fast the amplifier recovers from T/R switch feed-through and how far down that riniging is after x microseconds.

Regards, Joerg

Hello John,

But it's around $1.50 and single sourced. I wouldn't hold my breath unless you designed it into something that runs into the millions of units per year.

These European companies could generate a lot more sizzle for their chips if they knew how to design a good web site. Meaning a fast and engineer-friendly version.

Yes. That's essentially why we have work. If it was easy it would already be done wherever engineers are cheapest.

ROFL!

That's all being outsourced anyways. Except for paint, of course.

Regards, Joerg

The chip pulls notional equality with the LM324. Used so many of 'em the ST bean counters daren't pull the 'obsolete' stunt, (yeah ... in my dreams).

Weirdness, unknowns, ringdowns and feedthroughs are (of course!) part of the fun of electronics. If looking for a quieter life, I'd start off counting beans and if that was too exciting, maybe find a career watching paint dry, escalating to maybe doing some C++/C/C#/java/delphi/VB ... programming :). regards john

The old ca3262, quad gated inverting power driver with independent current- and temp-limits on each output?

That's a nice part, for video frequencies. I see they updated the datasheet in 2000, now complete with schematic and spice model.

"Joerg" a écrit dans le message de news:ACbCe.3779$ snipped-for-privacy@newssvr21.news.prodigy.com...

ST

dreams).

the

dry,

:).

That one can be outsourced too. You just need a webcam on the paint side. Then a single manned shop can watch many walls drying. One can specialize on just one color to even be more boring.

Yes. Small mercies!. Their datasheet still though looks like a scruffy, throwaway scan. OTOH, I do a lot of video security equipment. The gating aspect is a godsend. regards john