What should I look for buying Opamps?

[AllanBertelsen]

I need an opamp as OPA2340 https://www.ortodoxism.ro/datasheets/texasinstruments/opa2340.pdf
In the shop where I'm looking for components they don't have this particular one.
But everywhere you can get LM324. Would that be an OK alternative? I mean, isn’t all those opams nearly the same?
I don’t have much experience with opams. Please tell me someone, what are the most important characteristics to look for when choosing opamps?

 

[Nigel Goodwin]

What are you wanting to use it for?, different opamps are suitable for different uses - an LM324 is an really ancient quad device, with a VERY low spec. The Texas TL0xx series are pretty good general purpose ones, suitable for many uses, and of quite high quality as well.

 

[AllanBertelsen]

It's for an ultrasonic receiver like the one on figure 2 in this pdf
**broken link removed**

 

[mneary]

That circuit is designed for a gain of about 75 (21 db) at 40 kHz. This is beyond the capability of the LM324 and right on the edge even for the TL0xx. The second stage is a comparator (using the same amp). This could be slower if needed. Also, the circuit uses a single 5V supply, and although we know 5V works on the older opamps, it isn't specified.

The OPA2340 is designed for 2.7V (and up) and has the required bandwidth.

If you can provide a list of what's available to you, maybe someone can sort it out. It could also be built with transistors (5 or 6 per channel) if you're clever.

 

[AllanBertelsen]

I'm not clever when it comes to analogue circuits. I feel a lot more comfortable at digital circuits.
I have been looking for components at rapidonline. **broken link removed**
In my project a mobile ultrasonic transmitter should send a signal and three or more receivers should pick up the signal at a distance of 10 to 40 meters (30 to 130 feet).
I have been looking at this project https://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2004/vsn2/webpage/appendix_b.html that does not use op-ams, but I doubt that it would work at these distances.

 

[AllanBertelsen]

What about this one?
TLC27L4CN **broken link removed**
Can it be used as both amplifier and comparator?

 

[AllanBertelsen]

What about this one?
TLC27L4CN **broken link removed**
Can it be used as both amplifier and comparator?

No - I think it is to slow.

But what about LM324 - It operate down to 3V single supply. Bandwidth at 1Mz. Voltage gain at 100db. Is this the values I should be evaluating on?

 

[Nigel Goodwin]

No - I think it is to slow.

But what about LM324 - It operate down to 3V single supply. Bandwidth at 1Mz. Voltage gain at 100db. Is this the values I should be evaluating on?

No, as we've already said, the LM324 is far too low a spec.

 

[AllanBertelsen]

I give up

I give up.
Sorry for the trouble.
I have been studying ultrasonic transducers. They will never be able to work at a distance of more than 6 meters.

 

[audioguru]

The schematic for the ultrasonic receiver has the correct pins numbers but has the symbols for the + and - inputs backwards.

 

[mneary]

But what about LM324 - It operate down to 3V single supply. Bandwidth at 1Mz. Voltage gain at 100db. Is this the values I should be evaluating on?

LM324 has 100db gain at DC, but only unity gain at around 1 MHz. That's with a 30V supply. It's worse at 10V, and they don't even publish bandwidth data for 5V.

 

[Hero999]

The second stage is a comparator (using the same amp).

Be careful when using op-amps as comparators.
https://www.electro-tech-online.com/custompdfs/2007/04/sloa067.pdf
https://www.analog.com/UploadedFiles/Application_Notes/46875282066493AN_849.pdf

 

[gramo]

I still use the LM324 in "buffer" applications with PIC micro's. Single supply, & dirt cheap, sure there’s a little noise - but its negligible for most low key projects

 

[Nigel Goodwin]

I still use the LM324 in "buffer" applications with PIC micro's. Single supply, & dirt cheap, sure there’s a little noise - but its negligible for most low key projects

There's nothing with LM324's, but you need to be aware of their limitations (as with any device) and also that they are extremely old and low spec. Audioguru does seem a little paranoid about them though, and 741's as well

 

[audioguru]

I aren't paranoid about the buzzing crossover distortion that comes from an old LM324 when it has 100% negative feedback which reduces it but doesn't eliminate it.
Others on the web also joke about its horrible distortion.
One person measured 3% crossover distortion. He reduced it to only 0.002% by adding a pullup resistor so that one of its output transistors operates in class-A:

 

[Hero999]

You also tend to love the TL/7x/8x series, though is it can oscillate when driving a capacitive load.

 

[audioguru]

The TL07x and TL08x opamps have FET inputs. When their negative-going input common-mode voltage range is exceeded then they suddenly invert the signal when you don't expect it. Newer Fet input opamps don't do dat.

 

[mneary]

The TL0[7,8]x series also isn't any good on a 5V supply. Data sheet starts at +/-5 (10V total).

They do some things well, but before designing you definitely need to look at the data sheet. Most of the specs are almost the same: Bandwidth, output current, and power consumption in particular. The LM324 has a lower minimum operating voltage, better common mode performance, and the TL0[7,8]x series has lower bias current, the phase reversal problem, and instability with capacitive loads.

 

[gramo]

The TL07x and TL08x opamps have FET inputs. When their negative-going input common-mode voltage range is exceeded then they suddenly invert the signal when you don't expect it. Newer Fet input opamps don't do dat.

Sounds good, What newer FET opamps would they be?

 

[audioguru]

Sounds good, What newer FET opamps would they be?

Texas Instruments Burr Brown OPA134 single, OPA2134 dual and OPA4134 quad opamps have FET inputs but don't have the phase inversion problem of older ones.