MA780 – 8-BIT TO 12-BIT LOW-POWER ANGLE SENSOR

MA780 Rev. 1.2

MonolithicPower.com

27

8/30/2021

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APPENDIX A: DEFINITIONS

Effective Resolution

(3σ Noise Level)

Smallest angle increment distinguishable from the noise. The resolution

is measured by computing three times

σ (the standard deviation in

degrees) taken over 1,000 data points at a constant position. The bit

resolution is calculated as: log2(360 / 6σ).

Refresh Rate

Rate at which new data points are stored in the output buffer.

Latency

The time elapsed between the instant when the data is ready to be read

and the instant at which the shaft passes that position. The lag in degrees

is lag = latency x v, where v is the angular velocity (in deg/s).

Power-Up Time

Time until the sensor delivers valid data beginning at start-up (VDD <

3V).

Start-Up Time

Time until the sensor front end delivers valid data to the digital treatment

block when recovering from idle mode.

Filter Settling Time

Time for the filter to deliver a stable angle (i.e. when the error is smaller

than the noise at the particular filter window setting).

Integral Nonlinearity

(INL)

Maximum deviation between the average sensor output (at a fixed

position) and the true mechanical angle (see Figure A1).

Figure A1: Resolution, INL, Lag

INL can be obtained from the error curve err(a) = out(a) - a, where out(a)

is the average output across 1000 sensor outputs, and a is the

mechanical angle indicated by a high precision encoder (<0.001 deg).

INL can be calculated with Equation (A1):

max(err(a)) - min(err(a))

INL =

2

(A1)

Drift

The angle variation rate when one parameter is changed (e.g.

temperature, VDD) while all the others, such as the shaft angle, remain

constant.