AS3911 datasheet(13/149 Pages) AMSCO

13 / 149 page

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

AS3911 – 13

Detaile d Desc rip t ion

Transmitter

The transmitter incorporates drivers which drive external

antenna through pins RFO1 and RFO2. Single sided and

differential driving is possible. The transmitter block

additionally contains a sub-block which modulates transmitted

signal (OOK or configurable AM modulation).

The AS3911 transmitter is indented to directly drive antennas

(without 50

Ω cable, usually antenna is on the same PCB). Oper-

ation with 50

Ω cable is also possible, but in that case some of

the advanced features are not possible.

Receiver

The receiver detects transponder modulation superimposed on

the 13.56MHz carrier signal. The receiver contains two receive

chains (one for AM and another for PM demodulation) which

are composed of a peak detector followed by two gain and

filtering stages and a final digitizer stage. The filter

characteristics are adjusted to optimize performance over

different ISO modes and bit rates (sub-carrier frequencies from

212 kHz to 6.8 MHz are supported). The receiver chain inputs

are RFI1 and RFI2 pins; output of digitizer stage is demodulated

sub-carrier signal. The receiver chain incorporates several

features which enable reliable operation in challenging phase

and noise conditions.

Phase and Amplitude Detector

The phase detector is observing the phase difference between

the transmitter output signals (RFO1 and RFO2) and the input

signals RFI1 and RFI2. Signals RFI1 and RFI2 are proportional to

the signal on the antenna LC tank. RFI1 and RFI2 signals are also

used to run the self-mixer which generates output proportional

to their amplitude. The phase detector and self-mixer blocks

are used for several purposes:

• PM demodulation by observing RFI1 and RFI2 phase

variation (LF signal is fed to the Receiver)

• Average phase difference between RFOx pins and RFIx

pins is used to check antenna tuning

• Output of mixer is used to measure amplitude of signal

present on pins RFI1 and RFI2

A/D Converter

The AS3911 contains a built in A/D Converter. Its input can be

multiplexed from different sources and is used in several

applications (measurement of RF amplitude and phase,

calibration of modulation depth…). The result of A/D

conversion is stored in a register which can be read through the

SPI interface.

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