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OPA1656: High-Performance CMOS Audio Op Amp

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C

ClaudeG

Member
Joined 2015
Seems sadly TI sample program is restricted, perhaps not open to non US residents any more? Or it is the activity of the company, who knows...

No worries, will purchase some at Mouser when avail.

Meanwhile, to the lucky ones... please confirm/infirm it sounds exactly as OPA1656 :)

Claude
 
J

johnc124

Member
Joined 2006
soundanalog.com/
mcphervi said:
Hi Johnc124 - I'm looking at building a simple unity gain buffer with the OPA1656. Is the chip stable with output connected directly to the -ve terminal or is there a recommended feedback resistor? Not going to lie, the equation discussion on page 22 of the datasheet is marginally over my head..
Thanks!

https://e2e.ti.com/blogs_/archives/...resistors-in-the-feedback-of-a-buffer-ask-why
Click to expand...
The OPA1655 should be stable with the output connected directly to the inverting input, assuming you don't have large capacitive loads directly on the output.
 
S

sound signal

Member
Joined 2008
the.sound-signal.com
Hi @johnc124,

Re. distortion due to source impedance with the OPA1656 and common mode input signal voltages: do you have any data for that, or for the same mechanism with the OPA627 which you say the OPA1656 improves upon? I have not been able to find any.

johnc124 said:
The OPA1641 [...] has the most stable input capacitance vs. common mode voltage that I've measured on any op amp. When we developed the OPA1656, this was also a major design target [...]

This article shows the measurements I took on the OPA164x family. [...]

The performance of the CMOS audio op amps is actually fairly close and maybe slightly better than the OPA627, which was somewhat famous for its performance in this use case.
Click to expand...

With best wishes for the festive season and the new year.
 
M

MarcelvdG

Member
Joined 2003
MOS transistors are known for their large 1/f noise, although you can reduce it as much as you like by using very large gate area devices, at the expense of more chip area and more capacitance.

Still, I think 1/f noise is overrated for audio. When you take into account A- or ITU-R 468-weighting, it doesn't contribute all that much to the total noise.
 
B

BrianL

Member
Joined 2002
I doubt that the OPA1656 is made on a jellybean CMOS process. You usually don't get 40V supply capability on such a process. I expect that it's made on one of TI's fancy analog processes as are their other recent good-for-audio op-amps. I expect the process has bipolar (both genders), JFETs and CMOS transistors available to the chip designers. Note that the OPA1656 is described as 'FET-input', and I expect a lot of the remaining circuitry is bipolar transistors.
 
X

xtraforcz

Member
Joined 2018
Being a relatively cheap op-amp, it is very unlikely to be made in fancy processes.

As John said in several previous posts, OPA1656 is made on a quite mature CMOS process. Thus, I speculate that it is an old technology, say, 0.6um or 0.35um, that has been optimized for analog application.
 
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