ICS844S42I Datasheet, PDF (5/27 Pages) Integrated Device Technology – On-chip crystal oscillator for reference frequency generation

ICS844S42I Data Sheet
DUAL OUTPUT RF FREQUENCY SYNTHESIZER
Device Configuration
The ICS844S42I supports an output frequency range of 81MHz to
2592MHz. The output frequency f_OUT is a function of the reference
frequency f_REF and the three internal PLL dividers P, M, and N. f_OUT
can be represented by this formula:
f_OUT = (f_REF ÷ P) · M ÷ (NA, NB)
The M, N and P dividers require a configuration by the user to
achieve the desired output frequency. The output dividers NA, NB
determine the achievable output frequency range (see Table 3A).
The PLL feedback-divider M is the frequency multiplication factor
and the main variable for frequency synthesis. For a given reference
frequency f_REF, the PLL feedback-divider M must be configured to
match the specified VCO frequency range in order to achieve a valid
PLL configuration:
f_VCO = (f_REF ÷ P) · M and 1296MHz  f_VCO  2592MHz
The output frequency may be changed at any time by changing the
value of the PLL feedback divider M. The smallest possible output
frequency change is the synthesizer granularity G (difference in f_OUT
when incrementing or decrementing M). At a given reference
frequency, G is a function of the PLL pre-divider P and post-divider
N:
G = f_REF ÷ (P · NA, NB)
The purpose of the PLL pre-divider P is to situate the PLL into the
specified VCO frequency range f_VCO (in combination with M). For a
given output frequency, P = ÷4 results in a smaller output frequency
granularity G, P = ÷2 results a larger output frequency granularity G
and also decreases the PLL bandwidth compared to the P = ÷4
setting. The following example illustrates the output frequency range
of the ICS844S42I using a 16MHz reference frequency.
Table 3A. Device Configuration Table for f_REF = 16MHz)
Output Frequency (MHz) NA, NB
M
P
1296 – 2592
324 – 648
4
1
162 – 324
2
648 – 1296
324 – 648
4
2
162 – 324
2
432 – 864
324 – 648
4
3
162 – 324
2
324 – 648
324 – 648
4
4
162 – 324
2
216 – 432
324 – 648
4
6
162 – 324
2
162 – 324
324 – 648
4
8
162 – 324
2
81 – 162
324 – 648
4
16
162 – 324
2
G (MHz)
4
8
2
4
1.33
2.66
1
2
0.66
1.33
0.5
1
0.25
0.5
ICS844S42BKI REVISION A FEBRUARY 21, 2012
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©2012 Integrated Device Technology, Inc.