AMG-SM101 Datasheet, PDF (4/17 Pages) alpha microelectronics gmbh – Inductive Proximity Sensor IC

4. Block Diagram
AMG-SM101
Inductive Proximity Sensor IC
OscOut
OscIn
Vlin
Vcc
4,5V
4,5V
A
Y
B
S0
D_LED
P_LED
Rh
NO/NC
Vref
1,2V
Figure 2: Block Diagram
Monoflop
OUTN
Rcl
300mV
Ccl
5. Block Descriptions
5.1. LC Oscillator
The LC oscillator utilises the operational amplifier OA featuring a high gain-bandwidth product. The
positive feedback of this operational amplifier produces negative resistance at Pin OSCin to
compensate for energy losses in an external LC tank.
The LC oscillator generates a sinusoidal 100kHz…1MHz signal as long as no metallic object is present
within the sensing range of the sensor. As soon as a metallic object is placed in close proximity of the
external inductor (called proximity transducer in proximity detection applications) its Q factor drops due
to eddy currents induced in the object. This leads to higher energy losses in the LC tank, and if the
distance between the transducer and the object is small enough, the oscillations are broken.
5.2. Oscillation Detector
This block, consisted of a peak detector, low-pass filter and comparator with hysteresis, determines
whether the oscillator oscillates or not. It also implements a hysteresis function. The output of the
detector is used to drive, through the NO/NC multiplexer, the output drivers of the chip. The detector
features a dedicated pin Cdet to connect an external capacitor controlling the cut-off frequency of the
low-pass filter. This low pass filter eliminates malfunction of the sensor in the presence of short
interfering signals which might be received by the magnetic field-sensitive inductive transducer.
Therefore, if the IC is expected to work in a ‘harsh’ environment it is advised that the value of CF be
increased at the expense of reaction time of the IC.
AMG-SM101 Revision: B
06.11.12
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