Forums

TI opamp

Started by John Larkin March 10, 2015
On Wednesday, 11 March 2015 01:52:37 UTC+11, John Larkin  wrote:
> On Tue, 10 Mar 2015 11:28:27 +0100, David Brown > <david.brown@hesbynett.no> wrote: > > >On 10/03/15 04:53, bitrex wrote: > >> John Larkin <jlarkin@highlandtechnology.com> Wrote in message: > >>> > >>> > >>> Has anybody used this one? > >>> > >>> http://www.ti.com/product/lme49990 > >>> > >>> Sounds too good to be true. > >>> > >>> > >>> -- > >>> > >>> John Larkin Highland Technology, Inc > >>> picosecond timing laser drivers and controllers > >>> > >>> jlarkin att highlandtechnology dott com > >>> http://www.highlandtechnology.com > >>> > >>> > >> > >> I know audiophiles wet their panties over that one...if you do a > >> Google search on it a lot of designs from audio enthusiast sites > >> pop up > >> > > > >/Real/ audiophiles don't use opamps ! > > /Real/ audiophiles are notorious lunatics. I have a long list > somewhere around of idiotic audio terms, like "macrodynamics" and > "soundstaging" and "bass speed." > > This amp looks better than the LT1028. I hope it doesn't have a > similar noise peak off the graph.
The AD797 is another - better - alternative to the LT1028. I suggested it back in about 1997 when somebody was looking for an alternative to the LT1028, and the guys that tried it were pretty happy with it. http://www.analog.com/media/en/technical-documentation/data-sheets/AD797.pdf Some audiophiles used integrated circuits for more or less rational reasons. They aren't all lunatics. People like Peter Baxandall and Peter Walker qualified as audiophiles, but despised the subjectivists quite as much as you do - and probably for better reasons. -- Bill Sloman, Sydney
On Mon, 09 Mar 2015 20:36:05 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

> > >Has anybody used this one? > >http://www.ti.com/product/lme49990 > >Sounds too good to be true.
Probably BiCMOS. Look at the input bias current... bipolar input stage... could possibly be all bipolar given the 38V total supply capability. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 03/09/2015 11:36 PM, John Larkin wrote:
> > > Has anybody used this one? > > http://www.ti.com/product/lme49990 > > Sounds too good to be true. > >
I've looked at that part in the past, but never used it. It's quiet, like the ADA4898, runs off +-15V, has excellent linearity, and its PSR and CMR are amazing. Its main drawback is a crappy slew rate: 22 V/us for a 110 MHz GBW. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On 03/10/2015 10:57 AM, John Larkin wrote:
> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> > wrote: > >> On 3/9/2015 10:36 PM, John Larkin wrote: >>> >>> >>> Has anybody used this one? >>> >>> http://www.ti.com/product/lme49990 >>> >>> Sounds too good to be true. >> >> Note that the GBW is 110MHz on page 1 of the specs :) > > Yup. The ADI low-noise amps, still relatively noisy, are slow. The > LT1028 is below 1 nv/rthz but has issues. > >> >> Nice op-amp! > > Sure looks it. > > >
The ADA4898 is about 90 MHz, and the ADA4899 is 500 MHz GBW, though limited to +-5V. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Tue, 10 Mar 2015 11:55:07 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 03/09/2015 11:36 PM, John Larkin wrote: >> >> >> Has anybody used this one? >> >> http://www.ti.com/product/lme49990 >> >> Sounds too good to be true. >> >> >I've looked at that part in the past, but never used it. It's quiet, >like the ADA4898, runs off +-15V, has excellent linearity, and its PSR >and CMR are amazing. > >Its main drawback is a crappy slew rate: 22 V/us for a 110 MHz GBW. > >Cheers > >Phil Hobbs
But 22V/us is plenty good enough for audio... that's a "power" bandwidth of ~300kHz. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 03/10/2015 12:10 PM, Jim Thompson wrote:
> On Tue, 10 Mar 2015 11:55:07 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 03/09/2015 11:36 PM, John Larkin wrote: >>> >>> >>> Has anybody used this one? >>> >>> http://www.ti.com/product/lme49990 >>> >>> Sounds too good to be true. >>> >>> >> I've looked at that part in the past, but never used it. It's quiet, >> like the ADA4898, runs off +-15V, has excellent linearity, and its PSR >> and CMR are amazing. >> >> Its main drawback is a crappy slew rate: 22 V/us for a 110 MHz GBW. >> >> Cheers >> >> Phil Hobbs > > But 22V/us is plenty good enough for audio... that's a "power" > bandwidth of ~300kHz. > > ...Jim Thompson >
Sure thing. But clearly they traded off speed for other things. The classical 741-style architecture with no current boosters or emitter degeneration gets you a slew rate of about 0.3V*GBW, and this one is only 70% of even that. I guess they did that to get more phase margin, perhaps? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Tue, 10 Mar 2015 11:55:07 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 03/09/2015 11:36 PM, John Larkin wrote: >> >> >> Has anybody used this one? >> >> http://www.ti.com/product/lme49990 >> >> Sounds too good to be true. >> >> >I've looked at that part in the past, but never used it. It's quiet, >like the ADA4898, runs off +-15V, has excellent linearity, and its PSR >and CMR are amazing. > >Its main drawback is a crappy slew rate: 22 V/us for a 110 MHz GBW. > >Cheers > >Phil Hobbs
True. But it's cheap! -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Tue, 10 Mar 2015 08:55:02 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Mon, 09 Mar 2015 20:36:05 -0700, John Larkin ><jlarkin@highlandtechnology.com> wrote: > >> >> >>Has anybody used this one? >> >>http://www.ti.com/product/lme49990 >> >>Sounds too good to be true. > >Probably BiCMOS. Look at the input bias current... bipolar input >stage... could possibly be all bipolar given the 38V total supply >capability. > > ...Jim Thompson
Sure, the front end is likely giant NPNs with lots of current, to keep the voltage noise down. It probably has bias current cancellation, which makes the current noise worse, if anything. OP-27 sort of thing. Probably all bipolar. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Am 10.03.2015 um 15:57 schrieb John Larkin:
> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> > wrote: > >> On 3/9/2015 10:36 PM, John Larkin wrote: >>> >>> >>> Has anybody used this one? >>> >>> http://www.ti.com/product/lme49990 >>> >>> Sounds too good to be true. >> >> Note that the GBW is 110MHz on page 1 of the specs :) > > Yup. The ADI low-noise amps, still relatively noisy, are slow. The > LT1028 is below 1 nv/rthz but has issues.
The AD797 is not significantly noisier or slower, if at all. I really like the ADA4898-2. Depending on how it's measured, a little bit lower ft than the LME, but more than twice the slew rate, no 300 KHz noise mole hill like LT1028, and with 2 amplifiers/SO-8 quite a good price, especially if you average 20 devices for _really_ low voltage noise from low impedance sources. < http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > and, related: < http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf > < http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf > regards, Gerhard
On Tue, 10 Mar 2015 12:14:05 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 03/10/2015 12:10 PM, Jim Thompson wrote: >> On Tue, 10 Mar 2015 11:55:07 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 03/09/2015 11:36 PM, John Larkin wrote: >>>> >>>> >>>> Has anybody used this one? >>>> >>>> http://www.ti.com/product/lme49990 >>>> >>>> Sounds too good to be true. >>>> >>>> >>> I've looked at that part in the past, but never used it. It's quiet, >>> like the ADA4898, runs off +-15V, has excellent linearity, and its PSR >>> and CMR are amazing. >>> >>> Its main drawback is a crappy slew rate: 22 V/us for a 110 MHz GBW. >>> >>> Cheers >>> >>> Phil Hobbs >> >> But 22V/us is plenty good enough for audio... that's a "power" >> bandwidth of ~300kHz. >> >> ...Jim Thompson >> > >Sure thing. But clearly they traded off speed for other things. The >classical 741-style architecture with no current boosters or emitter >degeneration gets you a slew rate of about 0.3V*GBW, and this one is >only 70% of even that. I guess they did that to get more phase margin, >perhaps? > >Cheers > >Phil Hobbs
Probably phase margin. Slew rate, GBW, and phase margin are all interrelated with input stage current and the pole-splitting capacitor. See Op-Amp-Config.zip on the Device Models & Subcircuits Page of my website. Simply plugging into the subcircuit the parameters for slew rate, GBW and phase margin, from a datasheet, will get you quite close to actual performance. (I need to update that model to include swing limits, current limiting and rail currents... I know how, having done it making a model for a commercial customer... just haven't gotten round tuit ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.