For price, delivery and to place orders: Hittite Microwave Corporation, 20 Alpha Road, Chelmsford, MA 01824

Phone: 978-250-3343

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16

HMC701LP6CE

v09.1112

8 GHz 16-BIT FRACTIONAL-N PLL

a normal 3 sigma peak-to-peak variation in the arrival time therefore would be

if the synthesizer was in fractional mode, the fractional modulation of the Vco divider will dominate the jitter. the exact

standard deviation of the divided Vco signal will vary based upon the modulator chosen, however a typical modulator

will vary by about ±3 Vco periods, ±4 Vco periods, worst case.

if, for example, a nominal Vco at 5 GHz is divided by 100 to equal the reference at 50 MHz, then the worst case

division ratios will vary by 100±4. Hence the peak variation in the arrival times caused by Δ∑ modulation of the

fractional synthesizer at the reference will be

(EQ 11)

by the rms sum , where

(EQ 12)

in this example the jitter contribution of the phase noise calculated previously would add only 0.764psec more jitter at

the reference, hence we see that the jitter at the phase detector is dominated by the fractional modulation.

in summary, we have to expect about ±0.8 nsec of normal variation in the phase detector arrival times when in

fractional mode. in addition, lower Vco frequencies with high reference frequencies will have much larger variations.,

exhibit about ±4 nsec of peak variation at the phase detector, under normal operation. the lock detect circuit must not

confuse this modulation as being out of lock.

PFD Lock Detect

the Lock Detect circuit in the HMc701LP6cE places a one shot window around the reference. the one shot window

may be generated by either an analog one shot circuit or a digital one shot based upon an internal ring oscillator timer.

length, as shown in Figure 11. Setting lkd_ringosc_mono_select will result in a variable length ’digital’ window. the

digital one shot window is controlled by lkd_ringosc_cfg (Reg1Ah<16:15>). the resulting lock detect window period is

is enabled.

the lock detect window to declare lock. if for example we set lkd_wincnt_max = 1000 , then the Vco arrival would

have to occur inside the selected lock widow 1000 times in a row to be declared locked. When locked the Lock Detect

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