CS5378 datasheet(56/88 Pages) CIRRUS

56 / 88 page

CS5378

DS639F2

15. GAIN AND OFFSET CORRECTION

The CS5378 digital filter can apply gain and offset

corrections to the measurement data. Also, an off-

set calibration algorithm can automatically calcu-

late the offset correction value.

A gain correction value is written to the GAIN reg-

isters (0x21), while an offset correction value is

written to the OFFSET register (0x25). Gain and

offset corrections are enabled by the USEGR and

USEOR bits in the FILTCFG register (0x20).

When enabled, the offset calibration algorithm will

automatically calculate an offset correction value

and write it into the OFFSET register. Offset cali-

bration is enabled by writing the EXP and ORCAL

bits in FILTCFG.

15.1 Gain Correction

Gain correction in the CS5378 normalizes sensor

gain in multi-sensor networks. It requires an exter-

nally calculated correction value to be written into

the GAIN register (0x21).

A gain correction value is 24-bit two’s complement

with unity gain defined as full scale, 0x7FFFFF.

Gain correction always scales to a fractional value,

and can never gain the digital filter data greater

than one.

Output Value = Data * (GAIN / 0x7FFFFF)

Unity Gain: GAIN = 0x7FFFFF

50% Gain: GAIN = 0x3FFFFF

Zero Gain: GAIN = 0x000000

Once the GAIN register is written, the USEGR bit

in the FILTCFG register enables gain correction.

15.2 Offset Correction

Offset correction in the CS5378 cancels the DC

bias of a measurement channel by subtracting the

value in the OFFSET register (0x25) from the dig-

ital filter output data word.

An offset correction value is 24-bit two’s comple-

ment with a maximum positive value of 0x7FFFFF,

Figure 32. Gain and Offset Correction

FIR

IIR

Filters

Filter

Output to High Speed Serial Data Port (SD Port)

Offset

Correction

Output Rate 4000 SPS ~ 1 SPS

SINC

Filter

MDI Input

512 kHz

Correction

Gain

Offset

Calibration

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