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AS3930

Single Channel Low Frequency Wakeup Receiver

austriamicrosystems AG 

AS3930

Datasheet - Detailed Description

AS3930 needs the following external components:

Power supply capacitor – CBAT – 100 nF

32.768 kHz crystal with its two pulling capacitors – XTAL and CL (it is possible to omit these components if the internal RC oscillator is used

instead of the crystal oscillator)

Input LC resonator

In case the internal RC-oscillator is used (no crystal oscillator is mounted), the pin XIN has to be connected to the supply, while pin XOUT should

stay floating. Application diagrams with and without crystal are shown in Figure 1 and Figure 2.

8.1 Operating Modes

8.1.1 Power Down Mode

In Power Down Mode, AS3930 is completely switched off. The typical current consumption is 400 nA.

8.1.2 Listening Mode

In listening mode only the channel amplifier and the RTC are running. In this mode the system detects the presence of a carrier. In case the

carrier is detected, the RSSI can be displayed.

In this mode it is possible to distinguish the following three sub modes:

Standard Listening Mode. The channel amplifier that is capable of detecting the presence of the carrier frequency, is active all the time.

ON/OFF Mode (Low Power Mode). The channel amplifier is active for one millisecond after which it is switched off. The OFF-time is

programmable (see R4<7:6>).

Figure 11. ON/OFF Mode

Channel

t0

t0 + 1ms

Presence

of Carrier

t0 + T

t0 + T + 1ms

t0 + 2T

Time

Time

Further, for both sub modes, it is possible to enable a feature called Artificial Wake-up. If the Artificial Wake-up is enabled, then the AS3930

produces an interrupt after a certain time regardless of whether any activity is detected on the input. The period of the Artificial Wake-up is

defined in the register R8<2:0>. The user can distinguish between Artificial Wake-up and Wake-up based on the field detection (frequency or

pattern detection) since the Artificial Wake-up interrupt lasts only 128µs. With this interrupt the microcontroller (μC) can get feedback on the

surrounding environment (e.g. read the false wake-up register R13<7:0>) and/or take actions in order to change the setup.

8.1.3 Preamble Detection / Pattern Correlation

The preamble detection and pattern correlation are only considered for the wake-up when the data correlator function is enabled. See R1<1>.

The correlator searches first for preamble frequency (constant frequency of Manchester clock defined according to bit-rate transmission, see

Table 19) and then for data pattern.

If the pattern is matched, then the wake-up interrupt is displayed on the WAKE output and the chip goes in data receiving mode. If the pattern

fails, then the internal wake-up is terminated and no IRQ is produced.

www.ams.com/LF-Receiver/AS3930

Revision 1.5

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