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ST25R3911B датащи(PDF) 11 Page - STMicroelectronics |
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ST25R3911B датащи(HTML) 11 Page - STMicroelectronics |
11 / 129 page DocID029656 Rev 2 11/129 ST25R3911B Functional overview 71 1.1.1 Transmitter The transmitter incorporates drivers that drive external antenna through pins RFO1 and RFO2. Single sided and differential driving is possible. The transmitter block additionally contains a sub-block that modulates transmitted signal (OOK or configurable AM modulation). The ST25R3911B transmitter is intended to directly drive antennas (without 50 Ω cable, usually antenna is on the same PCB). Operation with 50 Ω cable is also possible, but in that case some of the advanced features are not available. 1.1.2 Receiver The receiver detects transponder modulation superimposed on the 13.56 MHz carrier signal. The receiver contains two receive chains (one for AM and another for PM demodulation) composed of a peak detector followed by two gain and filtering stages and a final digitizer stage. The filter characteristics are adjusted to optimize performance for each mode and bit rate (sub-carrier frequencies from 212 kHz to 6.8 MHz are supported). The receiver chain inputs are the RFI1 and RFI2 pins. The receiver chain incorporates several features that enable reliable operation in challenging phase and noise conditions. 1.1.3 Phase and amplitude detector The phase detector is observing the phase difference between the transmitter output signals (RFO1 and RFO2) and the receiver input signals (RFI1 and RFI2). The amplitude detector is observing the amplitude of the receiver input signals (RFI1 and RFI2) via self-mixing. The amplitude of the receiver input signals (RFI1 and RFI2) is directly proportional to the amplitude of the antenna LC tank signal. The phase detector and the amplitude detector can be used for the following purposes: • PM demodulation by observing RFI1 and RFI2 phase variation • Average phase difference between RFOx pins and RFIx pins is used to check and optimize antenna tuning • Amplitude of signal present on RFI1 and RFI2 pins is used to check and optimize antenna tuning 1.1.4 A/D converter The ST25R3911B contains a built in Analog to Digital (A/D) converter. Its input can be multiplexed from different sources and is used in several applications (measurement of RF amplitude and phase, calibration of modulation depth…). The result of the A/D conversion is stored in the A/D Converter Output Register and can be read via SPI. 1.1.5 Capacitive sensor The capacitive sensor is used to implement low power detection of transponder presence, it measures the capacitance between two copper patches connected to the CSI and CSO pins. The capacitance changes with the presence of an object (card, hand). During calibration the reference capacitance (representing parasitic capacitance of the environment) is stored. In normal operation the capacitance is periodically measured and compared to the stored reference value, if the measured capacitance differs from the stored reference value by more than a register defined threshold, then an interrupt is sent to the external controller. |
Аналогичный номер детали - ST25R3911B |
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Аналогичное описание - ST25R3911B |
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