AS3933 datasheet(20/64 Pages) AMSCO

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ams Datasheet

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[v1-08] 2015-Sep-02

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AS3933 − Detailed Description

Listening Mode

In listening mode, the chip is active and looks continuously for

the presence of the carrier on the input of all active channels.

In this mode, only the active channel amplifiers and the Clock

Generator are running. In case the carrier is detected, then the

RSSI measurements get started on all three channels and the

result is stored in the memory.

If the three dimensional detection is not required, then it is

possible to deactivate one or more channels. In case only two

channels are required, then the deactivated channel must be

the number two; while in case only one channel is needed, then

the active channel must be the number one.

Inside the listening mode, it is possible to distinguish the

following three low power sub modes:

Standard Listening Mode. All channels are active at the same

time.

Scanning Mode (Low Power Mode 1). In this sub-mode, a time

slot T=1ms is defined and in each time slot only one channel

can be active. As shown in Figure 21 when a certain time slot is

over, the current active channel is switched OFF and the next

channel becomes active and so on. If, for example all three

channels are enabled, in the first time slot the only active

channel is the number one. When the first time slot is over, the

channel one is switched OFF and the channel three becomes

active. During the third time slot, the channel two is active while

the other two are OFF. This channel rotation starts back from

the channel one and goes on until the presence of the carrier

is detected by any channel. The Scanning mode (channel

rotation) is managed internally by the AS3933 and doesn’t need

any activity from the host system (MCU). As soon as one channel

detects the frequency, all three channels become immediately

active at the same time. The AS3933 can perform a

simultaneous multidirectional evaluation (on all three

channels) of the field and evaluate which channel has the

strongest RSSI. The channel with the highest RSSI will be put

through to the demodulator. In this way it is possible to perform

multidirectional monitoring of the field with a current

consumption of a single channel, keeping the sensitivity as

good as if all channels are active at the same time.

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