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MC33596 Datasheet(PDF) 8 Page - Freescale Semiconductor, Inc |
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MC33596 Datasheet(HTML) 8 Page - Freescale Semiconductor, Inc |
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8 / 70 page 
MC33596 Data Sheet, Rev. 4 Frequency Planning Freescale Semiconductor 8 8.2 Intermediate Frequency The IF filter is controlled by the crystal oscillator to guarantee the frequency over temperature and voltage range. The IF filter center frequency, FIF, can be computed using the crystal frequency fref and the value of the CF bits: • If CF[0] = 0 : FIF = fref/9×1.5/2 • If CF[0] = 1 : FIF = fref/12×1.5/2 The cut-off frequency given in the parametric section can be computed by scaling to the FIF. Example 1. Cut-off Frequency Computation Compute the low cut-off frequency of the IF filter for a 16.9683 MHz crystal oscillator. For this reference frequency, FIF = 1.414 MHz. So, the 1.387 MHz1 low cut-off frequency specified for a 1.5 MHz IF frequency becomes 1.387 × 1.414/1.5 = 1.307 MHz. 8.3 Frequency Synthesizer Description The frequency synthesizer consists of a local oscillator (LO) driven by a fractional N phase locked loop (PLL). The LO is an integrated LC voltage controlled oscillator (VCO) operating at twice the RF frequency (for the 868 MHz frequency band) or four times the RF frequency (for the 434 MHz and 315 MHz frequency bands). This allows the I/Q signals driving the mixer to be generated by division. The fractional divider offers high flexibility in the frequency generation for: • Performing multi-channel links. • Trimming the RF carrier. Frequencies are controlled by means of registers. To allow for user preference, two programming access methods are offered (see Section 16.3, “Frequency Register”). • In friendly access, all frequencies are computed internally from the contents of the carrier frequency and deviation frequency registers. Table 4. Crystal Frequency and CF Values Versus Frequency Band RF Frequency (MHz) CF1 CF0 LOF1 LOF0 FREF (Crystal Frequency) (MHz) FIF (IF Frequency) (MHz) Dataclk Divider Fdataclk (kHz) Digclk Divider Fdigclk (kHz) Tdigclk (µs) 304 0 0 0 0 16.96745 1.414 60 282.791 30 565.582 1.77 315 0 0 1 0 17.58140 1.465 60 293.023 30 586.047 1.71 426 0 1 1 0 23.74913 1.484 80 296.864 40 593.728 1.68 433.92 0 1 0 1 24.19066 1.512 80 302.383 40 604.767 1.65 868.3 1 1 0 1 24.16139 1.510 80 302.017 40 604.035 1.66 916.5 1 1 1 1 25.50261 1.594 80 318.783 40 637.565 1.57 1. Refer to parameter 3.3 found in Section 19.3, “Receiver Parameters.” |
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