HMC704LP4E Datasheet, PDF (14/44 Pages) Hittite Microwave Corporation – 8 GHz fractionaL-N PLL

v04.0215
HMC704LP4E
8 GHZ FRACTIONAL-N PLL
where:
Φ2
p
f_o
f_pd
f_m
F_po
F_p1
Phase Noise Contribution of the PLL (rads²/Hz)
Frequency of the VCO (Hz)
Frequency of the Phase Detector (Hz)
Frequency offset from the carrier (Hz)
Figure of Merit (FOM) for the phase noise floor
Figure of Merit (FOM) for the flicker noise region
PLL Phase Noise
Contribution
( ) ^Φ
2
p
f₀, f_m, f_pd
= ^Fp1f02 + ^{Fp0 f02}
f_m
f_fd
PLL 1/f Flicker Noise
VCO 1/f3 Noise
VCO 1/f2 Noise
(EQ 1)
PLL Noise Floor
Typical Closed Loop Phase Noise
Closed Loop
Bandwidth
LOG OFFSET FREQUENCY (fm)
Figure 24. Figures of Merit Noise Models for the PLL
If the free running phase noise of the VCO is known, it may also be represented by a figure of merit for both 1/f² , F_v2,
and the 1/f³, F_v3, regions.
VCO Phase Noise
Contribution
( ) Φ_ν²
f₀ , f_m
=^Fν_fm2^f02
+
F_{ν 3} f₀₂
f_m³
(EQ 2)
The Figures of Merit are essentially normalized noise parameters for both the PLL and VCO that can allow quick esti-
mates of the performance levels of the PLL at the required VCO, offset and phase detector fre­quency. Normally, the
PLL IC noise dominates inside the closed loop bandwidth of the PLL, and the VCO dominates outside the loop band-
width at offsets far from the carrier. Hence a quick estimate of the closed loop performance of the PLL can be made by
setting the loop bandwidth equal to the frequency where the PLL and free running phase noise are equal.
The Figure of Merit is also useful in estimating the noise parameters to be entered into a closed loop design tool such as
Hittite PLL Design, which can give a much more accurate estimate of the closed loop phase noise and PLL loop filter
component values.
Given an optimum loop design, the approximate closed loop performance is simply given by the minimum of the PLL
and VCO noise contributions.
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