AS3911B datasheet(18/155 Pages) AMSCO

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AS3911B – 18

ams Datasheet: 2014-Jun-12 [v1-08]

A p pl i c at io n I n f o r m at i o n

Slow Transmitter Ramping

When transmitter is enabled it starts to drive the antenna LC

tank with full power, the ramping of field emitted by antenna

is defined by antenna LC tank Q factor.

However there are some reader systems where the reader field

has to transition with a longer transition time when it is

enabled. The STIF (Syndicat des transports d'Ile de France)

specification requires a transition time from 10% to 90% of field

longer than or equal to 10 μs.

The AS3911B supports that feature. It is realized by collapsing

VSP_RF regulated voltage when transmitter is disabled and

ramping it when transmitter is enabled. Typical transition time

is 15 μs at 3 V supply and 20 μs at 5 V supply.

Procedure to implement the slow transition:

• When transmitter is disabled set IO Configuration Register

2 bit slow_up to 1. Keep this state at least 2 ms to allow

discharge of VSP_RF.

• Enable transmitter, its output will ramp slowly.

• Before sending any command set the bit slow_up back

to 0.

Receiver

The receiver performs demodulation of the transponder

sub-carrier modulation which is superimposed on the

13.56MHz carrier frequency. It performs AM and/or PM

demodulation, amplification, band-pass filtering and

digitalization of sub-carrier signals. Additionally it performs

RSSI measurement, automatic gain control (AGC) and Squelch

function.

In typical application the Receiver inputs RFI1 and RFI2 are

outputs of capacitor dividers connected directly to the

terminals of antenna coil. Such concept assures that the two

input signals are in phase to the voltage on antenna coil. Care

has to be taken during design of capacitive divider that the RFI1

and RFI2 input signal pp value does not exceed the VSP_A

supply voltage.

Receiver comprises two complete receive channels for AM

demodulation and PM demodulation. In case both channels are

active the selection of channel used for reception framing is

done automatically by receive framing logic. The receiver is

switched on when Operation Control Register bit rx_en is set to

one. Additionally the Operation Control Register contains bits

rx_chn and rx_man; rx_chn defines whether both, AM and PM,

demodulation channels will be active or only one of them, while

bit rx_man defines the channel selection mode in case both

channels are active (automatic or manual). Operation of the

Receiver is controlled by four Receiver Configuration registers.

The operation of the receiver is additionally controlled by the

signal rx_on which is set high when modulated signal is

expected on the receiver input. This signal is used to control

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