Hallo Russell,

your reply make people think, that MCS1210 is showing extremely low noise performance. But the information you gave is rather confusing and questionable!

1. You defined ENOB (effective number of bits) as:

ENOB = 24 - log2(STDlsb)

What does this mean?

I learnt the following definition:

ENOB = (SNR - 1.76)/6.02

where 'SNR' is the actual Signal-to-Noise-Ratio, measured in deziBel (dB) and where 'ENOB' is measured in bits. How do the two definitions fit together?

2. You wrote:

If we look at the same 4 Hz data rate (15 Hz data rate) and a gain of 32 (+/- 78 mV) the decimation ratio will be 1023. That will give an ENOB of about 20 which is 149 nV of RMS noise.

You took the ENOB data from the figure of datasheet, which is valid for fdata = 10Hz. But for f-3dB = 4Hz you must take into account the noise performance referring to fdata = 15.3Hz according to the formula (sinc3-filter):

fdata = f-3dB / 0.262

If you take the data for fdata = 10Hz you get f-3dB = 2.62Hz and for this lowered bandwidth noise performance is some better, of course.
A first order approximation yields, that noise level is proportional to square root of bandwidth. This can be verified by reading datasheet of AD7730 and ADuC824. So, very probably, noise performance will be worse than what you have stated by the factor:

SQRT(4Hz / 2.62Hz) = 1.24

If you get 149nVeff in your calculation, real data will be 149nVeff x 1.24 = 185nVeff!

3. ENOB = 20 you get, if you take the data for 'Buffer OFF' condition. But having the buffer off has some disadvantages. Consequently, when comparing MCS1210 with others, having the buffer on, only 'Buffer ON' data should be taken. And then MCS1210 yields ENOB = 19 ...

4. Datasheet of AD7730 states in 'Table I' that for f-3dB = 4Hz and input voltage range of +-80mV output noise is 155nVeff. In 'Table II' they state, that this is equivalent to an resolution of 17.5 bits.
In your reply you state:

That will give an ENOB of about 20 which is 149 nV of RMS noise.

How the hell, can your 149nVeff, which is nearly the same as 155nVeff, give a resolution of 20 bits, when at the same time people of 'Analog Devices' say, that resolution is 17.5 bits??? This is totally confusing!!!

I guess, that when removing all these smart tricks, MCS1210 isn't any longer that superior!

Kai