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ATA5423 Datasheet(PDF) 10 Page - ATMEL Corporation |
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ATA5423 Datasheet(HTML) 10 Page - ATMEL Corporation |
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10 / 100 page  10 4841D–WIRE–10/07 ATA5423/ATA5425/ATA5428/ATA5429 3. RF Transceiver As seen in Figure 1-3 on page 6, the RF transceiver consists of an LNA (Low-noise Amplifier), PA (Power Amplifier), RX/TX switch, fractional-N frequency synthesizer and the signal process- ing part with mixer, IF filter, IF amplifier with analog RSSI, FSK/ASK demodulator, data filter, and data slicer. In receive mode the LNA pre-amplifies the received signal which is converted down to 226 kHz (ATA5423/ATA5428) and 235 kHz (ATA5425/ATA5429), filtered and amplified before it is fed into an FSK/ASK demodulator, data filter, and data slicer. The RSSI (Received Signal Strength Indicator) signal and the raw digital output signal of the demodulator are available at the pins RSSI and DEM_OUT. The demodulated data signal Demod_Out is fed to the digital control logic where it is evaluated and buffered as described in the section “Digital Control Logic” . In transmit mode, the fractional-N frequency synthesizer generates the TX frequency which is fed to the PA. In ASK mode the PA is modulated by the signal PA_Enable. In FSK mode the PA is enabled and the signal TX_DATA (FSK) modulates the fractional-N frequency synthesizer. The frequency deviation is digitally controlled and internally fixed to about ±16 kHz (see Table 4-1 on page 28 for exact values). The transmit data can also be buffered as described in the section “Digital Control Logic” . A lock detector within the synthesizer ensures that the transmis- sion will start only if the synthesizer is locked. The RX/TX switch can be used to combine the LNA input and the PA output to a single antenna with a minimum of losses. Transparent modes without buffering of RX and TX data are also available to allow protocols and coding schemes other than the internally supported Manchester encoding. 3.1 Low-IF Receiver The receive path consists of a fully integrated low-IF receiver. It fulfills the sensitivity, blocking, selectivity, supply voltage and supply current specification needed to manufacture, for example, an automotive remote control unit without the use of SAW blocking filter (see Figure 2-1 on page 7). In a Base-station Application (5V) the receiver can be used with an additional blocking SAW front-end filter as shown in Figure 2.2 on page 8. At 433.92 MHz the receiver has a typical system noise figure of 7.0 dB, a system I1dBCP of -30 dBm and a system IIP3 of –20 dBm. There is no AGC or switching of the LNA needed; thus, a better blocking performance is achieved. This receiver uses an IF (Intermediate Frequency) of 226 kHz, the typical image rejection is 30 dB and the typical 3 dB IF filter bandwidth is 185 kHz (f IF = 226 kHz ±92.5 kHz, flo_IF = 133.5 kHz and fhi_IF = 318.5 kHz). The demodulator needs a signal to Gaussian noise ratio of 8 dB for 20 Kbit/s Manchester with ±16 kHz frequency deviation in FSK mode; thus, the resulting sensitivity at 433.92 MHz is typically –106 dBm at 20 Kbit/s Manchester. Due to the low phase noise and spurious emissions of the synthesizer in receive mode (1) together with the eighth order integrated IF filter, the receiver has a better selectivity and block- ing performance than more complex double superhet receivers but without external components and without numerous spurious receiving frequencies. |
Similar Part No. - ATA5423_07 |
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Similar Description - ATA5423_07 |
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