[hpsdr] THD in Op Amps

[Arthur J. Lekstutis]

I subscribe to a Texas Instruments mailing list. Recently they announced 
an operational amplifier (OPA365) that attracted my attention. A big 
selling feature is that its "rail-to-rail input without crossover". That 
rings a bell from something I learned in school 30 years ago, and I 
probably should understand instantly, but I don't remember the details. 
I too often look at operational amplifiers as idealized black boxes.

They go on to compare this amplifier to "competitor" amplifiers, and 
graph the THD+Noise ratio vs. Vin=Vout (Vpp). Interestingly; they show 
very bad performance on the other amplifiers at high signal levels.

Are there many low THD+Noise amplifiers that suffer so badly at high 
signal levels, especially rail-to-rail? That would certainly be good to 
know. I would expect this to impact the large signal IMD significantly.

Later,
Artie Lekstutis
KC2MFS


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