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ST7537HS1 bảng dữ liệu(PDF) 3 Page - STMicroelectronics |
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3 / 9 page REFERENCE VOLTAGE CARRIER DETECTION Rx BAND-PASS S.C. FILTER Tx BAND-PASS S.C. FILTER CORRELATOR POST-DEMO S.C. FILTER FSK DEMODULATOR 27 5 13 12 11 10 7 6 9 8 FSK MODULATOR 17 16 18 19 24 20 22 23 I.F. BAND-PASS S.C. FILTER 3 26 4 21 2 14 28 15 1 25 RAI RxFO CD ATO PAFB PABC PABC RxD IFO XTAL1 XTAL2 MCLK WD RSTO Rx/Tx TxD DEMI TxIFI AVDD DV DD AVSS DV SS VCM DV CC TEST LOGIC TEST1 TEST2 TEST3 TEST4 ST7537HS1 BLOCK DIAGRAM TRANSMIT SECTION The transmit mode is set when Rx/Tx = 0, if Rx/Tx is held at 0 longer than 1 second, then the device switches automatically in the Rx mode. A new activation of the Tx mode requires Rx/Tx to be returned to 1 for a minimum 2 microsecond period before being set to 0. The Transmit Data (TxD) enter asynchronously the FSK modulator with a nominal intra-message data rate of 2400 bps. The basic transmit frequencies are : - f(TxD=0) = 133.05kHz - f(TxD=1) = 131.85kHz These frequencies are synthesized from a 11.0592MHz crystal oscillator; their precision is the same as the crystal one’s (100ppm). The modulated signal coming out of the FSK modu- lator is filtered by a switched-capacitor band-pass filter (Tx band-pass) in order to limit the output spectrum and to reduce the level of harmonic com- ponents. The final stage of the Tx path consists of an opera- tional amplifier which needs a feed-back signal (PAFB) from the power amplifier as shown on Application Schematic Diagram. In Tx mode the Receive Data (RxD) signal is set to 1. RECEIVE SECTION The receive section is active when Rx/Tx = 1. The Rx signal is applied on RAI and filtered by a band-pass switched capacitor filter (Rx band-pass) centered on the carrier frequency and whose band- width is around 12kHz. The Rx filter output is amplified by a 20dB gain stage which provides symetrical limitations for large voltage. The resulting signal is down-con- verted by a mixer which receives a local oscillator synthesized by the FSK modulator block. Finally an intermediate frequency band-pass filter (IF band- pass) whose central frequency is 5.4kHz improves the signal to noise ratio before entering the FSK demodulator. The coupling of the intermediate frequency filter output (IFO) to the FSK demodulator input (DEMI) is made by an external capacitor C5 (100nF ±10%, 10V) which cancels the Rx path offset voltage. The RxD output delivers the demodulated signal if the carrier detect (CD) signal is low and is set to high level when CD = 1. The RxD output can delivers the demodulated signal whatever the level of CD (0 or 1) if Rx/Tx = 1 and TxD = 0 (see Figure 1). ST7537HS1 3/9 |
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