AMS AS3933 Manual - Página 9

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AS3933 Standard Board

4.2.3 Clock Generator

The clock source for the AS3933 can be selected here. The AS3933 Demoboard has an on-board

crystal oscillator that is used by default. In case the RC oscillator is used it can be calibrated to

achieve a higher precision.

The RC oscillator can be calibrated via the microcontroller or the LC antenna.

The antenna can be damped in order to limit the range. Therefore a resistor inside the AS3933 is

switched into parallel to the antenna. The value of the resistor can be selected between 1kΩ to

27kΩ.

The performance of the Demodulator can be optimized according to the bit rate and preamble

length. For a higher bit rate the time constant needs to decrease. Adjust the Envelope Detector's

time constant according to your symbol rate. The recommended time constants for different symbol

rates are listed in the datasheet.

There are two possibilities to set the threshold level for the Data Slicer: the dynamic threshold and

the absolute threshold. The absolute threshold is set by selecting the hard threshold enable bit. In

quit environments (no noise sources present) the absolute threshold can be reduced by additionally

setting the hard threshold reduction bit. The dynamic threshold is enabled automatically when the

hard threshold enable bit is not set.

In case the dynamic threshold is enabled the noise immunity of the Data Slicer can be adjusted via

the Data Slicer time constant. Increasing this time constant will result in improved noise immunity

only if the minimum preamble length is also adjusted. Therefore, it is not possible to select a

specific Data Slicer time constant in the GUI but different minimum preamble lengths. The Data

Slicer's time constant is internally linked to this setting. The recommended minimum preamble

lengths for different Data Slicer time constants are listed in the datasheet.

The Data Slicer's comparator hysteresis can be adjusted between 20mV and 40mV. Furthermore,

the data slicer hysteresis can be active for either only positive edges or for both (positive and

negative) edges.

The Gain Reduction of the channel amplifier can be selected between 0dB up to -24dB. When the

setting AGC UP-DOWN is selected the maximum achievable gain is also defined by this setting.

4.2.10 Gain Reduction

The Frequency Detection Tolerance can be tighter or more relaxed. For details please see the

datasheet.

ams Demo Kit Manual, Confidential

Page 9

[v1-02] 2014-Jul-11

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