AS3909 datasheet(11/77 Pages) AMSCO

11 / 77 page

ams Datasheet, Confidential: 2013-Oct [3-02]

AS3909/AS3910 – 11

Detaile d Desc rip t ion

Transmitter

The Transmitter incorporates drivers, which drive external

antenna through pads RFO1 and RFO2. Single sided and

differential driving is possible. The transmitter block

additionally contains a subblock, which modulates transmitted

signal for communication reader to transponder (OOK or

configurable AM modulation).

The AS3909/10 transmitter is indented to directly drive

antennas (without 50

Ω cable, usually antenna is on the same

PCB). Operation 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 chain is composed of

a peak detector followed by two stages with gain and filtering

function and a final digitizer stage. The filter characteristics are

adjusted to optimize performance over different ISO modes and

data rates (subcarrier frequencies from 212 kHz to 848 kHz are

supported). The receiver chain input is the RFI1 pin; output of

digitizer stage is demodulated subcarrier signal. Receiver also

contains a subblock, which helps to detect the presence of

external RF field in NFCIP target mode. The receiver chain

incorporates several features, which enable reliable operation

in challenging phase and noise conditions.

Phase and Amplitude Detector

The phase detector observes the phase difference between the

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

RFI1 and RFI2. The pad 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:

• Variation of RFI1 and RFI2 phase is used to perform PM

demodulation

• Average phase difference between RFOx pins and RFIx

pins is used to check antenna tuning and inductive

wake-up via MCU

• Output of mixer is used to measure amplitude of signal

present on pins RFI1 and RFI2

A/D Converter

The AS3909/10 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, calibration of

modulation depth, checking of the antenna LC tank resonance,

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