HMC701LP6CE Datasheet, PDF (18/46 Pages) Hittite Microwave Corporation – 8 GHz 16-Bit Fractional-N Synthesizer

v03.0709
HMC701LP6CE
8 GHz 16-Bit Fractional-N Synthesizer
Frequency Change & VCO AutoCal
The HMC701LP6CE will update the active registers described above only when a frequency change is requested.
a. When in fractional mode (dsm_integer-mode Reg12h<3>=0) frequency change happens when the fractional
register is written (Reg10h Table 27). Integer register may be written first and is buffered until the frac register
is written.
b. When in Integer mode (dsm_integer-mode Reg12h<3>=1) frequency change happens when the integer
register is written (Reg0Fh Table 26). Frac register is not used.
c. If dsm_autoseed is enabled (Reg12h(7)=1), a frequency change updates the seed value of the fractional
modulator digital phase accumulator (DPA) with the value from the seed register Reg11h Table 28.
d. If a step tuned VCO is used and Auto tuning is enabled (Reg 0Ah(1)=1), then the frequency change will also
initiate the VCO autotuning calibration. Serial Port transfer to the VCO will happen automatically at the end of
the autotuning procedure. The VCO will update its registers on the last clock tick of the VSCK (see VCO Serial
Port WRITE Operation).
e. If a step tuned VCO is used and Auto tuning is disabled (Reg 0Ah(1)=1), then the frequency change will also
initiate the VCO Serial Port transfer to the VCO. The VCO will update its registers with the value from spivco_
direct_data (Reg0Bh Table 22) on the last clock tick of the VSCK (see VCO Serial Port WRITE Operation).
Buffering of the integer frequency value, seed value and vco tuning value allows the synthesizer and VCO to hold the
current frequency while new values are written. The synthesizer prescaler will only change when a valid frequency
change is written. If a step tuned VCO is used, and autotune is disabled, the VCO will be updated after the end of the
VCO Serial Port write cycle, about 16 clock cycles after the frequency change command.
Step Tuned VCO AutoCal on Frequency Change
Setting vcot_auto_start (Reg0Ah<0> Table 21) will cause the switched resonator VCO calibration to start automatically
whenever a frequency change is requested.
Step Tuned VCO Manual Calibration
Setting vcot_man_start (Reg0Ah<1>=1 Table 21) starts a switched resonator VCO calibration cycle for the current
programmed frequency. dsm_auto_start (Reg0Ah<0>=0) must be cleared. The value of the current VCO switch
setting determined by the calibration cycle is readable in the spivco_direct_data (Reg0Bh Table 22) register.
Step Tuned VCO Calibration Time & Accuracy
If a switched resonator VCO, is used, it may be calibrated by searching for the nearest resonator switch position that
yields the closest free running VCO frequency to the programmed frequency of the synthesizer. The measurement is
done with the VCO open loop and the varactor tuning port forced to VPPCP/2.
The VCO frequency is divided by 32 and counted for T_mmt. T_mmt is equal to 2vcot_ncyc_rdiv periods of the reference
crystal times vcot_xrefdiv_sel Reg0A<11:10> Table 21. The frequency result is the value in the vco counter, VCTR, as
shown in Figure 18. Currently only vcot_xrefdiv_sel = 1 is supported.
The nominal VCO frequency measured, f_vcom, is given by
(EQ 1)
Where the worst case measurement error, f_erro, is:
11
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