HMC701LP6CE Datasheet, PDF (13/40 Pages) Hittite Microwave Corporation – 8 GHz 16-Bit Fractional-N Synthesizer

v09.1112
HMC701LP6CE
8 GHz 16-BIT FRACTIONAL-N PLL
Internal Synchronized Frac strobe with clocks (gpo_sel= 4)
Setting register gpo_sel=4 in (Reg1Bh<3:0> Table 37) gives visibility into the internally synchronized strobe that
is generated when commanding a frequency change by writing to the frac register. The internal strobe initiates the
update to the fractional modulator. The internal frac strobe, the ref path divider output and the sine reference input are
buffered out to GPO1,GPO2 and GPO3 respectively as shown in Figure 8. In this mode, GPO1 may be used to trigger
an external instrument when doing frequency hopping tests for example.
Figure 8. gpo_04 Outputs
Δ∑ Modulator Phase Accumulator (gpo_sel=6)
Setting register gpo_sel=6 (Reg1Bh<3:0> Table 37) assigns the three msb’s of the delta sigma modulator first
accumulator to GPO<3:1>, where GPO3 is the msb. This feature provides insight into the phase of the VCO.
Auxiliary Oscillators (gpo_sel=7)
Setting register gpo_sel=7 (Reg1Bh<3:0> Table 37) assigns an auxiliary clock, an internal ring oscillator, and the
internal sigma delta clock to GPO3, 2, 1 respectively. The control of the auxiliary clock is determined by Reg18h Table
34 and Reg19h Table 35. In general terms, this highly flexible clock source allows the selection of one of the various
VCO or crystal related clocks inside the synthesizer or the selection of a flexible unstabilized auxiliary ring oscillator
clock. Any of the sources may be routed out via gpo_sel=7. Additional Reg18h Table 34 clock controls allow the aux
clock to be delayed by a variable amount (auxclk_modesel Reg18h<3:2>), or to be divided down by even values from
2 to 14 (auxclk_divsel Reg18h<6:4>).
Δ∑ Modulator Outputs (gpo_sel=10)
Setting register gpo_sel=10 (Reg1B<3:0> Table 37) assigns the three lsb’s of the delta sigma modulator output to
GPO<3:1> , where GPO1 is the lsb. This feature allows the possibility of using the HMC701LP6CE as a general
purpose digital delta sigma modulator for many possible applications.
External VCO
The HMC701LP6CE is targeted for ultra low phase noise applications with an external VCO. The synthesizer has
been designed to work with VCOs that can be tuned nominally over 0.5 to 4.5 Volts on the varactor tuning port with a
+5V charge pump supply voltage. Slightly wider ranges are possible with a +5.5V charge pump supply or with slightly
degraded performance. An external opamp active filter is required to support VCOs with tuning voltages above 5V.
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