Other Parts Discussed in Thread: OPA211, OPA189, LMP7731
The OPA2210 has exceptionally low noise temperature (optimum noise resistance calculated by dividing the input voltage noise by the input current noise and noise temperature calculated by determining at which temperature an ohmic resistor having that resistance value generates the same voltage and current noise as the amplifier input), being about 160k @ 1Hz and about 70k above 1kHz.
Furthermore, the optimum noise resistance is quite stable over frequency (similar 1/f corner frequencies for voltage and current noise).
Unfortunately, the optimum noise resistance is about 5kohm (rising to about 5.8kohm in the flicker region), which is quite high for many applications.
Is there a similar OpAmp from TI with a lower optimum noise resistance but similarly low noise temperature (especially at 0.1 to 10Hz)?
If not, is an according amplifier planned?
If both would not be the case, may I suggest this as a new product?
If you would increase the current of the input differential stage by a factor of about 6 to 7, then the optimum noise resistance would decrease by the same factor and the noise voltage would be like 2.5 times lower while the noise current would be 2.5 times higher. Maybe it would be advisable to increase the geometry of the input transistors (like take what is now in the OPA2210 and just put 3 additional input transistor pairs aside to the existing one, quadrupling the emitter area) in order to keep the flicker corner frequency about the same (I assume flicker noise might not scale as linearly with collector current, but if it would, the extra emitter area might not even be necessary).
With these measures, you could bring the input voltage noise down to values only achieved by the famous LT1128/1028 while even beating it with respect to flicker current noise to quite an extent (the LT1028 has about 66k noise temperature above 1kHz at about 800 ohms noise resistance, pretty much the same as my above proposed amplifier, but it has about 372k at about 127 ohms noise resistance at 1Hz, which would be clearly beaten by the presumed 160k at about 930 ohms noise resistance of an OPA2210 modified to about 6.25 times of input stage current).
If then there was also a slightly decompensated version (like the LT1028 is with respect to its 1128 brother), there would finally be a new king of low noise in the low frequency low source impedance area.
Even if there would be just an unity gain stable version, I would soo love to buy it and I am sure many others would too.
Many thanks in advance for considering my suggestion (I still hope that you are just about to announce that very product tomorrow).