HMC700LP4 Datasheet, PDF (19/36 Pages) Hittite Microwave Corporation – 8 GHz 16-Bit Fractional-N PLL

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HMC701LP6CE
8 GHz 16-Bit Fractional-N PLL
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Frequency Programming
The HMC701LP6CE can operate in either fractional mode or integer mode. In integer mode of operation the delta
sigma modulator is disabled. Frequency programming and mode control is described below.
Fractional Frequency
The fractional frequency synthesizer, when operating in fractional mode, can lock to frequencies which are fractional
multiples of the reference frequency.
Fractional mode is the default mode. To run in fractional mode ensure that dsm_integer_mode Reg12h<5> Table 29
is clear and dsm_rstb Reg01<13> Table 12). Then program the frequency as explained below:
The output frequency of the synthesizer is given by, f_vco, where
Fractional Frequency
of VCO
(EQ 13)
where
N_int

N_frac
R
f_xtal
As an Example:
f_xtal
R
f_ref
N_int
N_frac
is the integer division ratio, an integer number between 36 and 65,533
(dsm_intg (Reg0Fh Table 26))
is the fractional part, a number from 1 to 2²⁴ (dsm_frac Reg10h Table 27)
is the reference path division ratio, (rfp_div_ratio Reg03h<13:0> Table 14)
is the frequency of the crystal oscillator input (XSIN or XREF Figure 4)
= 50 MHz
=1
= 50 MHz
= 46
=1
(EQ 14)
In this example the output frequency of 2,300,000,002.98 Hz is achieved by programming the 16-bit binary value of
46d = 2Eh = 0000 0000 0010 1110 into dsm_intg.
Similarly the 24-bit binary value of the fractional word is written into dsm_frac,
1d = 000 001h = 0000 0000 0000 0000 0000 0001
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