AS3909 Просмотр технического описания (PDF) - austriamicrosystems AG
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AS3909 Datasheet PDF : 77 Pages
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Application Information
certain segments when driving the non modulated level to
reduce the amplitude of signal on the antenna and/or to reduce
the antenna Q factor.
The driver impedance in increased in case of AM modulation
(ISO-14443B), in case of OOK modulation (ISO-14443A) both
drivers are blocked to low state. In the single driver mode (bit
sing of configuration register 2 set to 1) only RFO1 output is
driven, RFO2 output is disabled.
AM modulation and operation of the driver segments is
controlled by writing AM modulation depth and antenna driver
registers (see “AM Modulation Depth and Antenna Driver
Registers” on page 46). Register #13 defines which segments
will be used to define normal, non-modulated level. The default
setting is that all segments are used. Registers #10 to #12 are
used to define how the AM modulated level is set-up. It can be
set-up automatically by definition of modulation depth and the
direct command Calibrate Modulation Depth or by a direct
definition of segments which are turned off during AM
modulation.
Receiver
The receiver performs demodulation of the transponder
subcarrier modulation which is superimposed on the 13.56 MHz
carrier frequency. It performs AM or PM demodulation,
band-pass filtering and digitalization of subcarrier signals, 848,
424 and 212 kHz subcarrier frequencies are supported.
Additionally, it performs RSSI measurement, automatic gain
control (AGC) and Squelch function.
The receiver is switched on when Operation Control Register bit
rx_en is set. 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 is
automatically done after every Transmit command. Signal
rx_on can be also forced high by sending direct command
Unmask Receive Data. Signal rx_on is used to control features
like RSSI and AGC.
AM demodulation is performed using a peak follower. Both the
positive and negative peaks are tracked to suppress common
mode signal. In case external demodulation is carried out the
peak follower stage can be bypassed by setting bit envi in
Configuration Register 2. In case of PM demodulation signal
coming from the phase detector is replacing the output of peak
follower.
Next stage in signal processing is the buffer amplifier followed
by second order low pass filter with adjustable corner
frequency. Final stage is a first order high pass filter with
adjustable corner frequency. The digital signal representing
transponder subcarrier modulation is produced by a window
comparator.
ams Datasheet, Confidential: 2013-Oct [3-02]
AS3909/AS3910 – 15
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