HMC702LP6CE Datasheet, PDF (23/38 Pages) Hittite Microwave Corporation – 14 GHz 16-Bit Fractional-N Synthesizer

v10.0812
HMC702LP6CE
14 GHz 16-BIT FRACTIONAL-N PLL

The frequency step size while ramping is controlled by rampstep, (Reg15h Table 26).
Frequency Step Size ∆ƒ_step = rampstep • f_xtal / 2²³ • R
where R is the value of the reference divider (rfp_div_ratio in Table 9)
Clearing or setting ramp_startdir_dn, (Reg14h<4> Table 25), sets the initial ramp direction to be increasing or
decreasing in frequency respectively. Setting ramp_singledir (Reg14h<7> Table 25), restricts the direction of the
sweep to the initial sweep direction only.
The sweeper timebase T_ref is the period of the divided reference, f_PFD, at the phase detector T_ref
The total number of ramp steps taken in a single sweep is given by ramp_steps_number in Reg16h Table 27.
The total time to ramp from f_o to f_f is given by T_ramp = T_{ref •} ramp_steps_number
The final ramp frequency, f_f, is given by ƒ_ƒ = ƒ_i + ∆ƒ_{step •} ramp_steps_number
Sweeper action at the end of sweep depends upon the mode of the sweep:
a. With both ramp_singledir and ramp_repeat_en disabled, at the end of the ramp time, T_ramp,
the sweeper will dwell at the final frequency f_f, until a new trigger is received. The next trigger will
reverse the current sequence, starting from f_f, and stepping back to f_o. Odd triggers will ramp in the
same direction as the initial ramp, even triggers will ramp in the opposite direction.
b. with ramp_singledir enabled and ramp_repeat_en disabled, at the end of the ramp time, T_ramp,
the sweeper will dwell at the final frequency f_f, until a new trigger is received. The second trigger
will hop the synthesizer back to the initial frequency, f_o. The third trigger will restart the sweep from
f_o. Hence all odd numbered triggers will start a new ramp in the same direction as the initial ramp,
even numbered triggers will hop the synthesizer from the current frequency to f_o , where it will wait
for a trigger to start a sweep.
Ramp Busy
In all types of sweeps ramp_busy will indicate an active sweep and will stay high between the 1^st and n^th ramp step.
ramp_busy may be monitored one of two ways. ramp_busy is readable via read only register Reg1Fh<5> Table 36.
ramp_busy may also be monitored on GPO2, hardware pin 24, by setting Reg1Bh<3:0> =8h Table 32.
Autosweep Mode
The Autosweep mode is similar to Figure 16 except that once started, triggers are not required. Once enabled, (ramp_
repeat_en=1 Reg14h<3> Table 25) the Autosweep mode initiates the first trigger, steps n times, one step per ref clock
cycle, and then waits for the programmed dwell period and automatically triggers the ramp in the opposite direction.
The sweep process continues alternating sweep directions until disabled. dwell_time (Reg17h Table 28) controls the
number of T_ref periods to wait at the end of the ramp before automatically retriggering a new sweep.
2-Way Sweeps
If ramp_repeat_en (Reg14h<3> Table 25) is cleared, then the ramps are triggered by
a. Writing to ramp_trigg (Reg14h<2> Table 25), if bit <2> = 0, or
b. by rising edge TTL signal input on GPO3, if ramp_trig_ext_en is set, and GPO3 is enabled.
All functions are the same in Figure 16 for Autosweep or 2-Way Triggered sweeps, the only difference is the trigger
source is generated internally for autosweep, and is input via serial port or GPO3 for triggered sweeps. Sweep_busy
will go high at the start of every ramp and stay high until the nth step in the ramp.
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