AS3911 datasheet(22/149 Pages) AMSCO

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AS3911 – 22

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

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

Digitizing Stage

Digitizing stage is producing a digital form of sub-carrier signal

which is output of Receiver and input to Framing Logic. It is a

window comparator with adjustable digitizing window (five

possible settings, 3 dB steps, adjustment range from ±33 mV to

±120 mV). Adjustment of the digitizing window is included in

AGC and Squelch loops or can be manually set in Receiver

Configuration Register 4.

AGC, Squelch and RSSI

As mentioned above second and third gain stage gain and the

Digitizing stage digitizing window are included in AGC and

Squelch loops. Eleven settings are available, default state

features minimum digitizer window and maximum gain, first

four steps increase the digitizer window in 3 dB steps, next six

steps additionally reduce the gain in 2nd and 3rd gain stage also

in 3 dB steps. The initial setting with which Squelch and AGC

start is defined in Receiver Configuration Register 4. The Gain

Reduction State Register displays the actual state of gain which

results from Squelch, AGC and initial settings in Receiver

Configuration Register 4.

Squelch

This feature is designed for operation of receiver in noisy

environment. The noise can come from tags in which

processing of data sent by the reader is going on and an answer

is being prepared. Noise can also be generated by noisy

environment. This noise may be misinterpreted as start of

transponder response which results in decoding error.

During execution of the Squelch procedure the output of

Digitizing comparator is observed. In case there are more than

two transitions on this output in 50 μs time period, gain is

reduced for 3 dB and output is observed during next 50 μs. This

procedure is repeated until number of transitions in 50 μs is

lower or equal to 2 or until maximum gain reduction is reached.

This setting is cleared by sending direct command Reset Rx

000

41.1

25.8

23.6

8.3

46.8

Automatic preset FeliCa (fc/64, fc/32)

Alternative choice for ISO14443 fc/32 and

fc/16

101

Alternative choice for fc/8 and fc/4

101

Automatic preset for fc/8 and fc/4

000

36.5

21.5

24.9

9.9

41.5

Automatic preset for NFCIP-1 (initiator and

target)

Gain [dB]

Comment

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