PS081 datasheet(37/155 Pages) AMSCO

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3-14

PSØ81

noise as low as 10nV at 3.3V can be achieved, or expressed in ENOB up to19.5 Bits (related to

2mV/V). An overview of the converter precision at different update rates is given in several tables

in section 2.4. However, a rough estimation can be done by the equations given in the following.

The base converter precision for a half bridge at avrate = 1 (only for calculation purposes, not re-

commended to be used) and a recommended discharge time of 90 to 150 µs in fast settling mode

and 2 mV/V excitation is:

With internal comparator:

13.3 Bit eff.

With external bipolar comparator: 13.8 Bit eff.

At higher values of avrate[] the resolution is calculated as:

The Bridge-factor is:

2 for full bridges

4 for quattro bridges

Example 1:

avrate = 12, Quattro bridge, internal comparator

ENOB = 13.3 + ln(

√(12*4))/ln(2) = 13.3 + 2.8 = 16.1 Bit eff. = 70,000 effective divisions =

10,000 peak-peak divisions in fast settle mode (without SINC-filter).

Example 2:

avrate = 450, Full bridge, external comparator

ENOB = 13.8 + ln (

√(450*2))/ln(2) = 13.8 + 4.9 = 18.7 Bit eff. = 425,000 effective divisions =

70,000 peak-peak divisions in fast settle mode (without SINC filter).

Example 3:

avrate = 100, Full bridge, external comparator, expressed in nV RMS

ENOB = 13.8 + ln (

√(100*2))/ln(2) = 13.8 + 3.8 = 17.6 Bit eff.

2^17.6 = 198,700 eff. divisions with a 2mV/V sensor operated at 3V

g 3V x 2mV/V = 6000µV

divided by 198,700 = 30.2nV RMS

Note: The effective number of bits (ENOB) in the equation are related to 2mV/V sensitivity of the

sensor. If the sensitivity is different with your sensor, the result needs to be corrected by the reduc-

tion in sensitivity. E.g.: you calculate 18.7 bit with the equation, but your sensor has only 1mV/V

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