I've been doing some designs operating off low supply voltages lately,
2-2.5 volts. The OPAx322 series is a really nice amp. 20 MHz, RRIO, 10 v/usec, runs down to 1.8 volts. They come off the rails clean not a problem at all it's hard to get them to mis-behave.They're a little too pricey to be called a jelly bean but in performance per dollar it blows away stuff like the AD8515.
That's very nice. Most modern rrio opamps come off the rails fast and clean, so make good comparators.
They tend to be stable with capacitive loads, too.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
It worked great for my low-voltage inductive transducer/sensor project to drive current into the inductor; the meander-wire transducer is a sloppy load with a lot of parasitic C but the amps handle it fine, and
65 mA drive per channel is pretty beefy for a low-voltage CMOS type.
The ST TSV99x is a cheaper alternative, one of the least expensive low-voltage RRIO CMOS types. But with somewhat worse specs on supply voltage range and noise. Also not unity-gain stable.
One unusual feature, they include an internal charge pump for the input transistors, eliminating a zero-offset-shift problem affecting most other RRIO op-amps. This adds 28us of extra startup time. The S version adds an enable pin.
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Thanks,
- Win
I noticed that and I also wondered what black magic they use to get the input voltage noise density so low despite there being a freaking switcher on the chip. It's still almost twice as good as some other amps around the same price point.
Black magic is the right word, they aren't telling.
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Thanks,
- Win
One old rrio, I think a Burr-Brown, with an internal power supply for the front end, ran the supply a some hundreds of MHz.
Hang a spectrum analyser probe near it!
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
A spectrum analyzer and impedance analyzer are next on the lab-to-buy list.
I could probably budget a HP 4192A or Wayne Kerr 6425 from the
80s-boatanchor-series for the latter. Don't know about the former
Aha, HP 4192A, a real workhorse. So many invaluable measurements.
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Thanks,
- Win
looks like it weighs as much as a horse, too. Gonna need a sturdier bench
They could have started with whatever the TPS60240 charge pump is doing:
"The dual-phase operation lowers the output ripple voltage significantly compared to a standard single-phase charge pump. In addition, the linear feedback of the operational amplifier eliminates the ripple during discharge of the output capacitor."
Regards, Clemens
There are some other tricks. See Jim Williams, "A Monolithic Switching
Plenty more info on google.
: y
So great how Williams put his personality into his app-notes. AN70 pg 13: "Note 14: The term ?cascode,? derived from ?cascade to cathode,? is applied to a configuration that places active devices in series. The benefit may be higher breakdown voltage, decreased input capaci- tance, bandwidth improvement, etc. Cascoding has been employed in op amps, power supplies, oscilloscopes and other areas to obtain performance enhancement. The origin of the term is clouded and the author will mail a magnum of champagne to the first reader correctly identifying the original author and publication"
I wonder if anyone won that champagne...
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