input bias current of a current-mode opamp

Started by John Larkin in sci.electronics.design7 years ago 6 replies

We think we've observed bias current drift on some THS3062 current-mode opamps, on the non-inverting input, roughly 10 uA in 6 months,...

We think we've observed bias current drift on some THS3062 current-mode opamps, on the non-inverting input, roughly 10 uA in 6 months, systematic in one direction across multiple amps. A regular opamp has, say, an NPN differential pair, identical transistors run at relatively low emitter and base currents. A current-mode opamp has PNP and NPN transistor bases on the ni input, with fa...


remarkable opamp

Started by John Larkin in sci.electronics.design3 years ago 44 replies

http://www.ti.com/product/OPA197/description The data sheet is as impressive as the part itself. It talks about the things that most opamp...

http://www.ti.com/product/OPA197/description The data sheet is as impressive as the part itself. It talks about the things that most opamp data sheets avoid. -- John Larkin Highland Technology, Inc lunatic fringe electronics


Another mistake

Started by George Herold in sci.electronics.design10 years ago 30 replies

Opps, I made another mistake. I=92ve got an opamp driving a unity gain power opamp. |\ OPA134 Vin---|+\ |\OPA544 | >...

Opps, I made another mistake. I=92ve got an opamp driving a unity gain power opamp. |\ OPA134 Vin---|+\ |\OPA544 | > --+----|+\ +-|-/ | | > --+--Vout | |/ | +-|-/ | +--10R--+ | |/ | | +-------+ R | GND With 10 ohms hanging on the output there is a bit of cross-over distortion. Hey, I thought, I=92ll just fe


interviews

Started by John Larkin in sci.electronics.design7 years ago 233 replies

We're interviewing design engineers and interns, all EE graduates or soon to be. So far, nobody knows the basics of what an opamp or a...

We're interviewing design engineers and interns, all EE graduates or soon to be. So far, nobody knows the basics of what an opamp or a transistor does. One guy, prompted, got an opamp output polarity right; we might hire him. This is good news for us, I suppose; what we do will be in increasing demand. All I need to do is hire smart people and teach them what I know. -- John Larki...


RRIO OpAmp Recommendation?

Started by Jim Thompson in sci.electronics.design7 years ago 15 replies

I need a rail-to-rail I/O OpAmp, 5V Vcc is fine, slow speed setting a current mirror. What would you guys in the discrete world recommend as...

I need a rail-to-rail I/O OpAmp, 5V Vcc is fine, slow speed setting a current mirror. What would you guys in the discrete world recommend as being well-behaved, no peculiarities, etc? (And readily available ;-) Thanks! ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations ...


Is it ok to use GBW as a lowpass?

Started by Piotr Wyderski in sci.electronics.design4 years ago 38 replies

Say I would like to amplify small signals at 100kHz, the opamp has GBW=3MHz, so I set gain to 20 in order to have bandwidth of 150kHz. What *in...

Say I would like to amplify small signals at 100kHz, the opamp has GBW=3MHz, so I set gain to 20 in order to have bandwidth of 150kHz. What *in practice* would happen to a 500kHz signal? The sim and a bench test show substantial attenuation, which is desired, but is it a general rule or just a property of a particular opamp? Could it cause any instabilities/distortion in the baseband? Be...


Comparator as operational amplifier

Started by Klaus Kragelund in sci.electronics.design4 years ago 25 replies

Hi So as always, I am looking for the last cent I have a design where I need a pretty fast opamp, something that settles the output within 1...

Hi So as always, I am looking for the last cent I have a design where I need a pretty fast opamp, something that settles the output within 1 us I have a free 25ns propagation delay comparator in the design, so I thought I could trick that comparator into changing gender to a opamp So first attempt was this: https://www.dropbox.com/l/scl/AAA0Q564c4zABf23i2HmIUbsbcyWmFTynLs (


2mV opamp

Started by Anonymous in sci.electronics.design7 years ago 74 replies

Hi folks I need a max 2mV offset opamp, and it needs to be as common as possible, found in discarded consumer appliances. I'm well rusted re...

Hi folks I need a max 2mV offset opamp, and it needs to be as common as possible, found in discarded consumer appliances. I'm well rusted re what offerings there are out there now - any suggestions? Sadly the 324 & 358 arent low offset enough, 061/071/081 are much higher offset, and 741/4558 are no good either. NT


OPA552 as power regulator

Started by John Larkin in sci.electronics.design3 years ago 42 replies

I need some programmable power supply rails, maybe -5 to +40 volts or so. We have some OPA552s in stock, a nice 60 volt power opamp. It's...

I need some programmable power supply rails, maybe -5 to +40 volts or so. We have some OPA552s in stock, a nice 60 volt power opamp. It's a decomp, and it will be driving a big capacitive load, so there is an oscillation hazard. One of my guys got the model from TI and kluged it into LT Spice. The symbol is ugly but it seems to work. We don't know how to make it look like a real opamp. ...


Bad OpAmp Spice Models?

Started by Jim Thompson in sci.electronics.design8 years ago 6 replies

I'm trying to make a list of OpAmp Spice models that either poorly model power supply currents, or not at all. Suggestions, hopefully with...

I'm trying to make a list of OpAmp Spice models that either poorly model power supply currents, or not at all. Suggestions, hopefully with details of how they deviate from the real device, would be appreciated. Thanks! ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations ...


OPAMP ASTABLE

Started by John Larkin in sci.electronics.design8 years ago 91 replies

I was thinking about building a small, low power dc/dc converter, +5 to maybe -25 volts, to bias a photodiode. I only need maybe 0.5 mA, but...

I was thinking about building a small, low power dc/dc converter, +5 to maybe -25 volts, to bias a photodiode. I only need maybe 0.5 mA, but I want the converter to be very quiet, which means no sharp switching edges or shoot-throughs. After futzing with a few ideas, I figured that a pair of r-r opamps, with reasonable slew rates, could do it. So, the opamp astable multivibrator. The comp...


Isolated high voltage opamp

Started by bitrex in sci.electronics.design7 years ago 21 replies

So I have a need for an analog isolation amplifier thing into a HV section at low audio frequencies. I remembered the "HV opamp" thing that...

So I have a need for an analog isolation amplifier thing into a HV section at low audio frequencies. I remembered the "HV opamp" thing that John Larkin posted a while back and that seems to work well, but I'd like to isolate the feedback via pwming it and sending it back across the barrier via an optocoupler and integrating. I dont really want to chop it first and have more LV elec...


HV OpAmp

Started by Jim Thompson in sci.electronics.design6 years ago 26 replies

HV OpAmp... Can be built to arbitrary HV supplies, just change Q1 and Q2 to higher voltage devices. ...

HV OpAmp... Can be built to arbitrary HV supplies, just change Q1 and Q2 to higher voltage devices. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC


PSRR match in dual opamp

Started by Allan Herriman in sci.electronics.design7 years ago 9 replies

Hi all, I was wondering about how well matched the PSRR is between the two channels of a dual opamp. Background: I have a physics...

Hi all, I was wondering about how well matched the PSRR is between the two channels of a dual opamp. Background: I have a physics package that has two outputs. Each output can be modelled as a floating voltage source with about 1Mohm source resistance. The voltages are tiny (uV), about the same amplitude as the Johnson noise of the source. The bandwidth is DC to about 50kHz. I...


filters

Started by John Larkin in sci.electronics.design10 years ago 15 replies

This cool. http://tinyurl.com/3jyxpke Click "filter expert" then "dual supplies." Then click on a box on one of the surfaces. I...

This cool. http://tinyurl.com/3jyxpke Click "filter expert" then "dual supplies." Then click on a box on one of the surfaces. I came up with a new-to-me filter architecture that *almost* works for me. It's a degenerated MFB lowpass, where the opamp itself replaces the usual opamp-r-c integrator. http://dl.dropbox.com/u/53724080/Circuits/MFB_hack.JPG This is freaky becau...


Using consumer-grade power amp as Power opamp

Started by Dave M in sci.electronics.design5 years ago 44 replies

Has anyone used any of the consumer-grade audio power amps such as the LM1825, TDA2030, or TDS7297 as a basic DC power opamp? Any reason they...

Has anyone used any of the consumer-grade audio power amps such as the LM1825, TDA2030, or TDS7297 as a basic DC power opamp? Any reason they shouldn't be used as power supply regulators, TEC controllers, etc? Dave M


G-Job Time, Need R-R I/O OpAmp

Started by Jim Thompson in sci.electronics.design9 years ago 2 replies

G-Job Time, Need R-R I/O OpAmp... Slow, so low GBW is OK But need VCC > = 8V Recommendations? ...

G-Job Time, Need R-R I/O OpAmp... Slow, so low GBW is OK But need VCC > = 8V Recommendations? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048


How close to rails?

Started by Anonymous in sci.electronics.design7 years ago 3 replies

Hi again This time designing a simple v to f using an opamp. Again it needs to use w= hatever parts are to hand from scrap consumer goods,...

Hi again This time designing a simple v to f using an opamp. Again it needs to use w= hatever parts are to hand from scrap consumer goods, nothing will be bought= . Question is how close to the rails can the inputs go while ensuring 90-95= % of opamps will work? I'm out of date regarding the opamps on the market. AFAICT the most common opamp out there in consumer gear is LM358. 324 is a=...


Problem with SCR.. or is it

Started by captoro in sci.electronics.design6 years ago 12 replies

Hello, I have an opamp driving the base of an SCR. Here is the...

Hello, I have an opamp driving the base of an SCR. Here is the circuit: https://www.dropbox.com/s/0w70dtwisqda6od/Message_1443999207152.jpg?dl=0 The output of the opamp is is great, Basically goes high when the + input receives a fainth signal. The problem is that the led does not always turn on, most of the time it does. I saw a few times the LED would light with no input. I chang...


How much current can an opamp source

Started by panfilero in sci.electronics.design8 years ago 2 replies

Hello, How do you figure out how much current an opamp can source from the datashe= et? I'm looking at this instrumentation amplifier...

Hello, How do you figure out how much current an opamp can source from the datashe= et? I'm looking at this instrumentation amplifier (datasheet link below) an= d the only things I find that relate to current is=20 link: http://www.ti.com/lit/ds/symlink/ina210.pdf Maximum Input Current to any pin is 5mA - which makes me think "any" includ= es power pins, which means this thing can't ...