ST25R3916 datasheet(27/157 Pages) STMICROELECTRONICS

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DS12484 Rev 4

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ST25R3916/7

Application information

156

Figure 7. Receiver block diagram

Demodulation stage

The first stage performs demodulation of the tag subcarrier response signal, superimposed

on the HF field carrier. Two different blocks are implemented for the AM demodulation:



peak detector



AM/I or PM/Q demodulator mixer.

The choice of the used demodulator is made by the Receiver configuration register 2 bit

amd_sel.

The peak detector performs AM demodulation using a peak follower. Both the positive and

negative peaks are tracked to suppress any common mode signals. Its demodulation gain is

G = 0.7 and the input is taken from RFI1 demodulator input only.

The AM demodulator mixer uses synchronous rectification of both receiver inputs (RFI1 and

RFI2). Its gain is G = 0.55. The PM demodulation is also done by a mixer. The PM

demodulator mixer has differential outputs with 60 mV differential signal for 1% phase

change (16.67 mV / °).

The I/Q demodulation is composed of two mixer circuits, driven with a 90° shifted local

oscillator (LO) signals derived from the crystal oscillator. The outputs of the two mixers are

connected to two equal base band reception chains and to the decoding logic.

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