CS5376 View Datasheet(PDF) - Cirrus Logic

Part Name

Description

MFG CO.

CS5376

Low Power Multi-Channel Decimation Filter

Cirrus Logic 

CS5376

the maximum and minimum data values from the

CS5376.

Relative Gain = [(maximum - minimum) / 2]

The lowest value of relative gain from all sensors in

a measurement network determines a standard gain

value.

Standard Gain = minimum relative gain

The gain correction value for a specific measure-

ment channel is calculated as the value required to

scale that sensor’s relative gain down to the stan-

dard gain value.

Gain Correction = [(standard gain / relative gain) *

0x7FFFFF]

Once calculated, a sensor’s gain correction value is

written to the GAIN register for that measurement

channel.

9.2 Offset Correction

Offset correction in the CS5376 is used to cancel

the DC bias in a measurement channel. It uses val-

ues from the OFFSET1, OFFSET2, OFFSET3, and

OFFSET4 registers to shift the output data and

eliminate systematic offsets. Offset correction val-

ues are 24-bit 2’s complement with a maximum

positive value of 0x7FFFFF (decimal 8388607),

and a maximum negative value of 0x800000 (deci-

mal 8388608).

Calculation of offset correction values is performed

manually using output data from each channel, or

automatically using the internal offset calibration

algorithm. When offset correction values are calcu-

lated manually, they must be written into the OFF-

SET registers. When using the offset calibration

algorithm, the calculated offset correction values

are written to the OFFSET registers automatically.

Once the OFFSET registers are written, the USE-

OR bit (bit 13) in the FILT_CFG register enables

offset correction.

Offset correction is a simple subtraction of the off-

set correction value from the output data, with

overflow protection ensuring the corrected value

does not exceed the maximum limits. If offset cor-

rection causes the output data to exceed a 24-bit 2’s

complement maximum, the output data value will

saturate.

Output Value = Data - Offset Correction

Max Positive Output Value = 0x7FFFFF

Max Negative Output Value = 0x800000

9.2.1 Offset Register Calculation

An offset correction value manual calculation uses

output data from the CS5376 when no signal is in-

put to the sensor. Background noise measurements

are averaged to determine the DC bias present in

the measurement channel.

DC Offset = [Sum(Noise Data) / Num Data]

Once determined, the manually calculated offset

correction value is written to the OFFSET register

for that channel.

9.3 Offset Calibration

An offset calibration algorithm is included in the

CS5376 to automatically calculate offset correction

values. When using the offset calibration algo-

rithm, no signal should be present on the sensor.

Background noise data is used to calculate an aver-

age offset value for each measurement channel.

Offset calibration is an exponential averaging func-

tion that places increased weight on current input

samples. The exponential weighting factor is set by

the EXP bits (bits 16-20) in the FILT_CFG regis-

ter. Increasing the exponent value applies greater

weight to earlier samples and produces a smoother

averaging function requiring a longer settling time.

Decreasing the exponent value applies greater

weight to later samples and produces a noisier av-

eraging function requiring a shorter settling time.

Typical exponential values range from 0x05 to

DS256PP1

66

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