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MICRF213AYQS Datasheet(PDF) 10 Page - Micrel Semiconductor |
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MICRF213AYQS Datasheet(HTML) 10 Page - Micrel Semiconductor |
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10 / 16 page  Micrel, Inc. MICRF213 May 2007 10 M9999-052307-A (408) 944-0800 the top layer close to the REFOSC pins RO1 and RO2. When care is not taken in the layout, and crystals from other vendors are used, the oscillator may take longer times to start as well as the time to good data in the DO pin to show up. In some cases, if the stray capacitance is too high (>20pF), the oscillator may not start at all. The crystal frequency is calculated by REFOSC = RF Carrier/(32+(1.1/12)). The local oscillator is low side injection (32 × 9.81563MHz = 314.1MHz), that is, its frequency is below the RF carrier frequency and the image frequency is below the LO frequency. Refer to Figure 6. The product of the incoming RF signal and local oscillator signal will yield the IF frequency, which will then be demodulated by the detector of the device. fLO f (MHz) Image Frequency Desired Signal Figure 6. Low Side Injection Local Oscillator REFOSC (MHz) Carrier (MHz) HIB Part Number 9.467411 303.825 SA-9.467411-F-10-H-30-30-X 9.81563 315 SA-9.815630-F-10-H-30-30-X 10.75045 345.0 SA-10.750450-F-10-H-30-30-X Table 5. Crystal Frequency and Vendor Part Number JP1 and JP2 are the bandwidth selection for the demodulator bandwidth. To set it correctly, it is necessary to know the shortest pulse width of the encoded data sent in the transmitter. Reference the example of the data profile, in the Figure 7, below: Figure 7. Example of a Data Profile PW2 is shorter than PW1, so PW2 should be used for the demodulator bandwidth calculation. The calculation is found by 0.65/shortest pulse width. After this value is found, the setting should be done according to Table 6. For example, if the pulse period is 140µsec, 50% duty cycle, then the pulse width will be 70µsec (PW = (140 µsec * 50%) / 100). So, a bandwidth of 9.286kHz would be necessary (0.65 / 70µsec). However, if this data stream had a pulse period with a 20% duty cycle, then the bandwidth required would be 23.2kHz (0.65 / 28µsec), which exceeds the maximum bandwidth of the demodulator circuit. If one tries to exceed the maximum bandwidth, the pulse would appear stretched or wider. SEL0 JP1 SEL1 JP2 Demod. BW (hertz) Shortest Pulse (usec) Maximum baud rate for 50% Duty Cycle (hertz) Short Short 1180 551 908 Open Short 2360 275 1815 Short Open 4720 138 3631 Open Open 9400 69 7230 Table 6. JP1 and JP2 Setting, 315MHz Capacitors C6 and C4, Cth and Cagc capacitors respectively, provide the time base reference for the data pattern received. These capacitors are selected according to data profile, pulse duty cycle, dead time between two received data packets and if the data pattern has or not a preamble. See Figure 7 for an example of a data profile. Other frequencies will have different demodulator bandwidth limits, which are derived from the reference oscillator frequency. Table 7 and Table 8, below, show the limits for the other two most used frequencies. SEL0 JP1 SEL1 JP2 Demod. BW (hertz) Shortest Pulse (usec) Maximum baud rate for 50% Duty Cycle (hertz) Short Short 1140 570 8770 Open Short 2280 285 1754 Short Open 4550 143 3500 Open Open 9100 71 7000 Table 7. JP1 and JP2 Setting, 303.825MHz SEL0 JP1 SEL1 JP2 Demod. BW (hertz) Shortest Pulse (usec) Maximum baud rate for 50% Duty Cycle (Hertz) Short Short 1290 504 992 Open Short 2580 252 1985 Short Open 5170 126 3977 Open Open 10340 63 7954 Table 8. JP1 and JP2 Setting, 345.0MHz |
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