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AS3935

Datasheet - Detailed Descri p ti on

8.7 Analog Front-end (AFE) and Watchdog

The AFE amplifies and demodulates the AC-signal picked up by the antenna. Since the AS3935 is a lightning sensor based on narrowband

receiving technique (center frequency of 500kHz and a bandwidth of about 33kHz), the AFE bandwidth is meant to be greater than the antenna

bandwidth. In this way, it is possible to consider that the gain within the antenna bandwidth as constant.

The gain of the AFE by default is optimized to operate indoor (e.g. inside a building). If the AS3935 operates outdoor, then the AFE gain setting

has to be set to a lower value, as shown in the Table 15. Indoor and Outdoor setting must be selected according to the type of the application.

The output signal of the AFE is monitored by the watchdog, which enables the signal validation (see Signal Verification on page 11) in case the

input signal crosses a certain threshold. The AS3935 is automatically set back to Listening Mode once the Signal Validation block has made an

assessment on the nature of the received signal (lighting or disturber). With register REG0x01[3:0] it is possible to change the level of this

threshold to increase the robustness to disturbers. If higher thresholds are used, the AS3935 would loose sensitivity for very far lightning events,

with an improvement of the man-made disturber rejection as benefit.

Figure 20 shows the degradation of the detection efficiency (sensitivity of lightning detection) over the distance for different threshold settings.

Figure 20. Detection Efficiencies vs. Distance for Different Settings for WDTH, if SREJ=0000

Table 15. AFE Setting, Outdoor vs. Indoor

AFE Setting

REG0x00[5:1]

Indoor

10010

Outdoor

01110

60%

40%

20%

0.0

0

10

20

30

40

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

Radius [km]

WDTH