am8192b RLS, am8192b Datasheet - Page 9

• Manufacturer Part Number: am8192b
• Description: Angular Magnetic Encoder Ic
• Manufacturer: RLS

Data sheet
AM8192BD01_05
Issue 5, 14
Hysteresis
The AM8192B uses an electrical hysteresis when converting analogue signals to digital. The hysteresis must
always be larger than the peak noise to assure a stable digital output. The effect is a position hysteresis when
rotating the magnet CW or CCW. Hysteresis is one of the configurable parameters of the interpolator.
Variation of hysteresis when the recommended value is set:
* Measured at slow movement to avoid delay caused by filtering.
** Standard deviation of the hysteresis measured on 3000 samples.
Noise and filtering
The AM8192B uses Hall sensors for detecting the magnetic flux distribution. Noise on the Hall sensors is
seen as noise on the output position. The noise can be represented as a standard deviation or peak value.
The peak value is 5 times larger than the standard deviation.
For reducing the noise an RC filter is used on the sine and cosine signals. 10 kΩ resistors and 120 pF
capacitors are inside the chip and external capacitors can be added. The recommended value for external
capacitors is 22 nF, but this can be changed if needed. Using an RC filter introduces an output position delay
when rotating at high speeds. Position delay can be calculated as follows:
At high rotational speed the analogue amplitude decreases. Normally, this amplitude drop is negligible. It
must only be considered in the combination of large frequency and large capacitors. The amplitude should not
drop below 0.5 V.
The hysteresis used must always be larger than the peak noise. If peak noise is larger than hysteresis, the
output direction could change even when magnet rotation direction is not. The interpolator always assures
that the incremental output will not have missing pulses. If the peak noise is larger than resolution,
intermediate pulses are generated. The intermediate pulses will be generated with minimal time distance t
Minimal time distance of generated pulses t
available resolutions table in the “Interpolator” section on page 7).
© 2009 RLS d.o.o.
Parameter
Hysteresis
Hysteresis standard deviation
th
January 2009
Fig. 10: Hysteresis
Δ
ϕ
=
Arc
tan
Symbol
Hyst
Hyst
{
f
/
STDEV
f
Δ
0
}
A
=
TD
1
Min.
0.06
−
is defined by the resolution setting of AM8192B (see the
1
f =
1
Typ.
0.17
0.035
+
Available typical hysteresis:
* Recommended value
⎛
⎜
⎝
frequency
A
Hysteresis
0
0.088
0.176
0.352
0.703
1.406
f
f
0
⎞
⎟
⎠
Max.
0.25
2
,
f
0
Unit
deg
deg
Unit
deg
deg
deg
deg
deg
deg
=
2 (
π
associate company
RC
Note
*
**
Note
= 360°/4096
= 360°/2048 *
= 360°/1024
= 360°/512
= 360°/256
)
−
1
TD
9
.