
p
ll
s
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6 - 20
HMC703LP4E
v02.0813
8 GHz fractional syntHesizer
For price, delivery and to place orders: Hittite Microwave Corporation, 2 Elizabeth Drive, Chelmsford, MA 01824
978-250-3343 978-250-3373 fax Order On-line at www.hittite.com
Application Support: pll@hittite.com
table 6. operational Modes
Register
Number
Register Name
PLL Operating Mode (SD_MODE =
0
1
2
3
4
5 to 7
Fractional
Mode
Integer Mode
Exact
Frequency
Mode
FM (Frequency
Modulation)
Mode
PM (Phase
Modulation)
Mode
Ramp Mode
Function of
N Integer Part
Nint
N
Nint
Freq 1: Nint
Nint
start Nint
Function of
N Fractional
Part
Nfrac
Freq 1: Nfrac
Nfrac
start Nfrac
Function of
Aux Register
Phase step
Frequency step
/ reference clock
Function of
Alternate
Integer
Freq 2: Nint
sTOP Nint
Function of
Alternate
Fractional
Channels / PD
frequency
Freq 2: Nfrac
sTOP Nfrac
Additional Functionality
Double Buffer
YEs
NO
YEs
On Trigger
Updates
frequency,
optionally
initiates phase
Updates
frequency,
optionally
initiates phase
Toggles
frequency (level
sensitive)
Increments /
decrements
phase
Proceeds to
next stage of
ramp
Those registers which are unused in a particular mode can take on any value, and are ignored.
triggering
Depending on the operating mode, a trigger event is used to change frequency, FM modulate the frequency, modulate
the phase, or advance the frequency ramp profile to its next state. In general the HMC703LP4E can be triggered via
one of three methods. Not all modes support all trigger methods.
1.
An external hardware trigger pin-6 (TRIG)
2.
3.
sPI write to fractional register
Reg 04h (frequency hopping triggers only).
Depending on the mode, the part is sensitive to either the rising edge, or the level of the trigger. The sPI’s TRIG bit
emulates the external TRIG pin, and so it must typically be written to 1 for a trigger, and then back to 0 in preparation
for another trigger cycle. To use the external TRIG pin, it must be enabled via EXTTRIG_EN
(Reg 06h[9]).
fractional Mode or exact frequency Mode frequency Updates
In non-modulated fractional modes (Reg 06h[7:5] = 0 or 2), if the external trigger is enabled, writes to NINT and Nfrac (Reg 03h and
Reg 04h) are internally buffered and wait for an explicit trigger via either the TRIG pin or the sPI’s TRIG
bit before taking effect. If EXTTRIG_EN = 0, the write to NINT is double-buffered, and waits for a fractional write to
information on calculating the fractional multiplier for your application.
initial Phase control
On the HMC703LP4E, the user has control of the initial phase of the VCO via the 24-bit sEED
Reg 05h. This seed
phase is loaded on the 1st clock cycle following a trigger event, provided that autoseed (Reg 06h [8] = 1) is enabled. The value in
Reg 05h represents the phase of the VCO. For example, if two synthesizers are triggered in parallel, but
one has a sEED of 0.2 (0.2x224) and the other has a sEED of 0.7 (0.7x224), the steady state outputs of the two VCOs