mc33696fje/r2 Freescale Semiconductor, Inc, mc33696fje/r2 Datasheet - Page 9

• Manufacturer Part Number: mc33696fje/r2
• Description: Mc33696 Pll Tuned Uhf Transceiver
• Manufacturer: Freescale Semiconductor, Inc

10
10.1 Clock Generator
All clocks running in the circuit are derived from the reference frequency provided by the crystal oscillator
(frequency f
has to operate.
10.2 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 f
of the CF bits:
The cut-off frequency given in the parametric section can be computed by scaling to the FIF.
10.3 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.
1. Refer to parameter
Freescale Semiconductor
Frequency
433.92
(MHz)
868.3
916.5
304
315
426
•
•
RF
If CF[0] = 0 : FIF = f
If CF[0] = 1 : FIF = f
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 1.375
1.375
Frequency Planning
ref
CF1
1
0
0
0
0
1
1
*1.414/1.5 = 1.296 MHz
, period t
Table 4
3.3
CF0
Table 4. Crystal Frequency and CF Values Versus Frequency Band
0
0
1
1
1
1
1
found in
MHz low cut-off frequency specified for a 1.5 MHz IF frequency becomes
shows the value of the CF bits.
ref
). The crystal frequency is chosen in relation to the band in which the MC33696
LOF1
0
1
0
0
0
1
Section 19.1, “General Parameters.”
ref
ref
/9*1.5/2
/12*1.5/2
Example 1. Cut-off Frequency Computation
LOF0
0
0
1
1
1
1
MC33696 Data Sheet, Rev. 9
F
Frequency)
REF
16.96745
17.58140
23.74913
24.19066
24.16139
25.50261
(MHz)
(Crystal
Frequency)
F
(MHz)
1.414
1.465
1.484
1.512
1.510
1.594
IF
(IF
Dataclk
Divider
60
60
80
80
80
80
282.791
293.023
296.864
302.383
302.017
318.783
F
(kHz)
dataclk
Divider
Digclk
30
30
40
40
40
40
Frequency Planning
ref
565.582
586.047
593.728
604.767
604.035
637.565
F
and the value
(kHz)
digclk
T
1.77
1.71
1.68
1.65
1.66
1.57
(µs)
digclk
9