HMC701LP6CE Datasheet, PDF (20/46 Pages) Hittite Microwave Corporation – 8 GHz 16-Bit Fractional-N Synthesizer

v03.0709
HMC701LP6CE
8 GHz 16-Bit Fractional-N Synthesizer
We arrive at a value of 10 for ncyc, and hence a single measurement period is T_mmt = 20.48 usec, the worst case
frequency error of the measurement is ±1.56 MHz and the total time to run the full calibration for a 5 bit switched VCO
is six measurements worst case, hence T_cal = 6 T_mmt = 122.9 usec, plus time for six VCO serial port transfers and state
machine housekeeping, typically about 90*R/f_xtal, about 1.8 usec more.
Example Calibration Procedure with an Example External VCO
Using the above example calculation for calibration time and accuracy, the procedure to run the calibration is as
follows using an example VCO at 2.3 GHz:
The example VCO must first be set up to operate in the desired band, with, in this example, a 50 MHz crystal and a
50 MHz PFD frequency.
a. Setup the VCO register as required by the VCO (Reg0Bh Table 22)
b. Input a reference signal at 50 MHz
c. Set the Ref divider to divide by 1 , rfp_div_ratio = 00 0000 0000 0001, (Reg03h<13:0> Table 14)
d. Set the integer division, intg = 46d = 002Eh (Reg0Fh Table 26)
Then set up the auto calibration features as follows:
e. Set the auto calibration time by setting vcot_ncyc_rdiv = 1010 (Reg0Ah<5:2> Table 21)
f. Enable the auto calibration feature by setting vcot_auto_start (Reg0Ah<0> Table 21)
Then program the fractional frequency to start the calibration and change frequencies.
g. Set the fractional register to zero in this example, frac = 000000h (Reg10h Table 27)
The last step of programming the frequency register initiates the calibration which will run in about 124 usec, as per
our calculation. The state machine will write the autotune result into Reg20h Table 42. The synthesizer will then be
tuned to the commanded output frequency with the optimized switch setting on the VCO. The normal locking time will
apply after the calibration is run.
The optimum tuning setting for this frequency may be read by the host from read only register vcot_caps Reg20h<7:0>
(Table 42) and stored for later use for faster tuning to this frequency.
Manual VCO Control for Fast Frequency Changes
If the auto calibration reading is run first for a given frequency and the calibration settings are read and stored for later
use in the host, then a frequency change can be run without re-running the autocal routine.
Assume that the VCO band and reference are all programmed correctly in advance. Further that we disable the auto
calibration feature by clearing vcot_auto_start (Reg0Ah<0> Table 21).
Then a frequency change is executed as follows:
a. Write the calibration switch setting for the desired frequency to spivco_direct_data (Reg0Bh Table 22).
(VCO specific)
b. If necessary set the integer frequency register dsm_intg (Reg0Fh Table 26)
c. Write the fractional register to trigger the frequency change frac (Reg10h Table 27)
d. The synthesizer then automatically updates the fractional divider and initiates the VCO Serial Port transfer
for the new frequency
Calibration Polarity, Tune Word Inversion & Active Opamp Loop Filters
vcot_invert_outdata (Reg0Ah<6> Table 21) inverts the VCO tuning cap polarity. The polarity must be set to match the
VCO polarity in question or the autotune search algorithm will not work. This bit is normally set if an active loop filter
is used with an inverting opamp with a positive tuning slope VCO
vcot_swap_outdata (Reg0Ah<7> Table 21) swaps the cap data left to right. This makes it easy to match the VCO in
use. Binary weighted caps are expected.
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