HMC700LP4 Datasheet, PDF (11/36 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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Prescaler and Reference Path Outputs (gpo_sel = 1)
Setting register gpo_sel=1 (Reg1B<3:0> Table 37) results in the input crystal being buffered out to GPO3 as shown
in Figure 6. This is useful for example to generate a copy of the input crystal signal to drive other circuits in the
application, while at the same time isolating the noisy circuits from the sensitive crystal output. Often only the
synthesizer requires very low phase noise from the crystal, hence it is desirable to isolate other circuits from the
crystal itself and allow the synthesizer sole use of the low phase noise crystal.
gpo_sel=1 also routes the 250 MHz 14-bit reference path divider to GP02 and the 16-bit 7 GHz VCO path prescaler
output to GP01. This option allows the synthesizer to function as a stand alone fractional or integer prescaler and
provides visibility into the prescaler and reference path timing for sensitive applications.
Figure 6. gpo_01 Outputs
Lock Detect Windows (gpo_sel=2)
Setting register gpo_sel = 2 (Reg1Bh<3:0> Table 37) results in the lock detect window (Figure 11) and the phase
frequency detector UP and DN output control signals (Figure 14) to be routed to pins GPO1, GPO3 and GPO2
respectively. This option gives insight into the Lock Detection Process and could allow the synthesizer to be used with
an external charge pump.
Figure 7. gpo_02 Outputs
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