ST25R3916B-AQWT datasheet(28/165 Pages) STMICROELECTRONICS

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Application information

ST25R3916B ST25R3917B

28/165

DS13541 Rev 7

The gain in the second and third stage is 23 dB and can be reduced in six 3 dB steps. Gain

of these two stages is included in AGC and Squelch loops or can be manually set in

Receiver configuration register 4. Sending of direct command Reset RX Gain is necessary

to initialize the AGC, Squelch and RSSI block. Sending this command clears the current

Squelch setting and loads the manual gain reduction from Receiver configuration register 4.

Second stage has a second order low-pass filtering characteristic, the pass band is adjusted

according to subcarrier frequency using the bits lp2 to lp0 of the Receiver configuration

Digitizing stage

The digitizing stage produces a digital representation of the sub-carrier signal coming from

the receiver. This digital signal is then processed by the receiver framing logic. The digitizing

stage consists of a window comparator with adjustable digitizing window (five possible

settings, 3 dB steps, adjustment range from ±33 to ±120 mV). The adjustment of the

digitizing window is included in the AGC and Squelch loops. The digitizing window can also

be set manually in the Receiver configuration register 4.

AGC, Squelch and RSSI

As mentioned above, the second and third gain stage gain and the digitizing stage window

are included in the AGC and Squelch loops. Eleven settings are available. The default state

features minimum digitizer window and maximum gain. The first four steps increase the

digitizer window in 3 dB steps, the next six steps reduce the gain in the second and third

gain stage, again in 3 dB steps. The initial start setting for Squelch and AGC is defined in

Receiver configuration register 4. The Gain reduction state register displays the actual state

of gain resulting from Squelch, AGC and initial settings in Receiver configuration register 4.

7 MHz

Others

Not used

Table 6. First and third zero setting

rec1<3>z600k rec1<2>h200

rec1<1>h80

rec1<0>z12k First stage zero Third stage zero

60 kHz

400 kHz

200 kHz

40 kHz

80 kHz

12 kHz

200 kHz

80 kHz

200 kHz

600 kHz

400 kHz

200 kHz

Others

Not used

Table 5. Low-pass control (continued)

rec1<5>lp2

rec1<4>lp1

rec1<3>lp0

-1 dB point

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