AS3911 datasheet(33/149 Pages) AMSCO

33 / 149 page

ams Datasheet, Confidential: 2013-Oct [2-03]

AS3911 – 33

Appl icatio n I n f o rm a t i o n

Figure 18:

Phase Detector Inputs and Output in case of 135º Phase

Shift

Amplitude Detector

Signals from pins RFI1 and RFI2 are used as inputs to the

self-mixing stage. Output of this stage is DC voltage

proportional to amplitude of signal on pins RFI1 and RFI2.

During execution of direct command Measure Amplitude this

output is multiplexed to A/D Converter input.

External field Detector

The External Field Detector is used to detect the presence of an

external device generating an RF field. It is automatically

switched on in NFCIP-1 active communication modes; it can

also be used in other modes. The External Field Detector

supports two different detection thresholds, Peer Detection

Threshold and Collision Avoidance Threshold. The two

thresholds can be independently set by writing the External

Field Detector Threshold Register. The actual state of the

External Field Detector output can be checked by reading the

Auxiliary Display Register. Input to this block is the signal from

the RFI1 pin.

Peer Detection Threshold

This threshold is used to detect the field emitted by peer NFC

device with which NFC communication is going on (initiator

field in case the AS3911 is a target and the opposite, target field

in case the AS3911 is an initiator). It can be selected in the range

from 75mVpp to 800mVpp. When this threshold is enabled the

External Field Detector is in low power mode. An interrupt is

generated when an external field is detected and also when it

is switched off. With such implementation it can also be used

to detect the moment when the external field disappears. This

VSP

VSP/2

VSP

AS3911 Datasheet(PDF) 33 Page - ams AG