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AS3931

Datasheet - Detailed Descr i pti on

8 Detailed Description

8.1 Block Diagram

Figure 13. Block Diagram

8.2 Block Description

8.2.1 Antenna Rotator

In order to achieve an optimum assignment of the antennas to the receiving channels, the connection of the antennas to the channels can be

changed cyclically with a multiplexed (antenna rotator), which is controlled by an internal register. The register setting can be changed by the

serial interface.

8.2.2 Input Attenuator

Input signal attenuation is provided for each channel by means of connecting a 1.5 k

Ω resistor across the differential inputs. An internal register

controls attenuation.

8.2.3 Input Shortcutting

The differential inputs can be shortened by register settings to measure the RSSI offset. In this case, the resistance between the differential

inputs is reduced to approximately 500

Ω.

8.2.4 Input Protection Circuit

Each signal input has a powerful input overload protection circuit consisting of two anti-parallel protection diodes connected to ground (see

Figure 14). This connection ensures that the differential input voltage can never exceed the supply voltage of the chip. To obtain proper

operation, the differential input receiving circuits (resonant RLC-circuits) must be floating and shall be grounded nowhere (see Figure 1)

LF1P

LF1N

LF2P

LF2N

LF3P

LF3N

CS

SCL

SDA

VCC

Input

Protection1

Input

Protection2

Input

Protection3

Antenna Rota-

tor

Input

Attenuator1

Input

Attenuator2

Input

Attenuator3

Log. Env. Amp 1

Log. Env. Amp 2

Log. Env. Amp 3

Detector1

Detector2

Detector3

RSSI

Multiplexer

Control Logic

Regulator

Regulator

POR

RSSI

Buffer

Data

Multiplexer

Wake Generator

Correlator3

Correlator2

Correlator1

Wake

AS3931