29 - 37
Data Sheet - D e t a i l e d D e s c r i p t i o n
Figure 23. Example of Linearity Error Over 360º
7.12.2 Transition Noise
Transition noise is defined as the jitter in the transition between two steps. Due to the nature of the measurement principle (Hall sensors +
Preamplifier + ADC), there is always a certain degree of noise involved. This transition noise voltage results in an angular transition noise at the
outputs. It is specified as 0.06 degrees rms (1 sigma)
1. This is the repeatability of an indicated angle at a given mechanical position. The
transition noise has different implications on the type of output that is used:
Absolute Output; SSI Interface: The transition noise of the absolute output can be reduced by the user by applying an averaging of read-
ings. An averaging of 4 readings will reduce the transition noise by 50% = 0.03º rms (1 sigma).
PWM Interface: If the PWM interface is used as an analog output by adding a low pass filter, the transition noise can be reduced by lower-
ing the cutoff frequency of the filter. If the PWM interface is used as a digital interface with a counter at the receiving side, the transition
noise may again be reduced by averaging of readings.
Incremental Mode: In incremental mode, the transition noise influences the period, width and phase shift of the output signals A, B and
Index. However, the algorithm used to generate the incremental outputs guarantees no missing or additional pulses even at high speeds (up
to 10.000 rpm and higher).
7.12.3 High Speed Operation
The AS5140H samples the angular value at a rate of 10.42k samples per second. Consequently, the incremental and the absolute outputs are
updated each by 96µs. At a stationary position of the magnet, this sampling rate creates no additional error.
Absolute Mode. With the given sampling rate of 10.4 kHz, the number of samples (n) per turn for a magnet rotating at high speed can be
In practice, there is no upper speed limit. The only restriction is that there will be fewer samples per revolution as the speed increases.
Regardless of the rotational speed, the absolute angular value is always sampled at the highest resolution of 10 bit. Likewise, for a given number
of samples per revolution (n), the maximum speed can be calculated by:
1. Statistically, 1 sigma represents 68.27% of readings; 3 sigma represents 99.73% of readings.