HMC701LP6CE Datasheet, PDF (22/40 Pages) Hittite Microwave Corporation – 8 GHz 16-Bit Fractional-N Synthesizer

v09.1112
HMC701LP6CE
8 GHz 16-BIT FRACTIONAL-N PLL
a. Stepped by an automatic sequencer, or
b. Single stepped by individual triggers in Single Step Mode.
Triggering of each sweep, or step, may be configured to operate:
a. Via a serial port write to Reg14h<2> ramp_trigg (if Reg 14h<2> = 0 )
b. Automatically generated internally,
c. Triggered via TTL input on GPO3 Reg14h<5> = 1.
Sweep parameters are set as follows:
Initial Frequency, f_o = Current frequency value of the synthesizer, (EQ 12)
Final Frequency, f_f = Frequency of the synthesizer at the end of the ramp
The frequency step size while ramping is controlled by rampstep, (Reg15h Table 31).
Frequency Step Size ∆ƒ_step = rampstep • f_xtal / 2²⁴ • R
where R is the value of the reference divider (rfp_div_ratio in Table 14)
Clearing or setting ramp_startdir_dn, (Reg14h<4> Table 30), sets the initial ramp direction to be increasing or
decreasing in frequency respectively. Setting ramp_singledir (Reg14h<7> Table 30), 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 32.
The total time to ramp from f_o to f_f is given by T_ramp = T_{ref •} ramp_steps_number
CW Sweeper Mode (Continued)
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 41.
ramp_busy may also be monitored on GPO2, hardware pin 24, by setting Reg1Bh<3:0> =8h Table 37.
Autosweep Mode
The Autosweep mode is similar to Figure 15 except that once started, triggers are not required. Once enabled, (ramp_
repeat_en=1 Reg14h<3> Table 30) 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 33) controls the
number of T_ref periods to wait at the end of the ramp before automatically retriggering a new sweep.
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