HMC703LP4E datasheet(21/52 Pages) HITTITE

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HMC703LP4E

v00.0311

8 GHZ FRACTIONAL SYNTHESIZER

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(not accounting for any mismatch) will be 180° out of phase = ((0.7-0.2) x 360°). The user can take advantage of this

for phase control of the outputs of multiple synthesizers.

If phase control is not needed, the best spurious operation is achieved with the SEED set to a busy binary number,

for example 50F1CDh, or B29D08h.

Note that in Exact Frequency mode with an exact step of fstep, if autoseed is off, there can be a delay of up to 1/fstep

after a trigger before a new fractional frequency is recognized.

Frequency Tuning

Integer Mode

In integer mode the VCO step size is fixed to that of the PD frequency, fpd. Integer mode typically has lower phase

noise than fractional mode for a given PD operating frequency. The advantage is usually of the order of 2 to 3 dB.

Integer mode, however, often requires a lower PD frequency to meet channel step size requirements. The fractional

mode advantage is that higher PD frequencies can be used, hence lower phase noise can often be realized. “Charge

Pump Offset” should be disabled in integer mode. In integer mode the Δ∑ modulator is shut off and the N divider (Reg

03h) may be programmed to any integer value in the range 16 to 216-1. To use the HMC703LP4E in integer mode

program Reg 06h[7:5] = 1, then program the integer portion of the frequency (as per (EQ 5)), ignoring the fractional

part.

There is no double buffering in integer mode, i.e. write data then trigger the frequency change later. A write to the

NINT register (Reg 03h) immediately starts the RF frequency hop. There is no external trigger available in this mode.

If double buffering is required, use fractional mode (Reg 06h[7:5] = 0), with Nfrac (Reg 04h ) = 0, and SEED (Reg 05h)

= 0.

Fractional Mode

The HMC703LP4E is placed into fractional mode by setting SD_MODE (Reg 06h[7:5] ) = 0

The frequency of a locked VCO controlled by the HMC703LP4E, fvco, is given by

fps =

(Nint + Nfrac) = fint + ffrac

fxtal

(EQ 5)

fvco = k fps

(EQ 6)

Where:

fps

is the frequency at the prescalar input after any potential RF divide by 2

fvco

is the frequency at the HMC703LP4E’s RF port

is 1 if the RF Divide by 2 is bypassed, 2 if on (Reg 08h[17])

Nint

is the integer division ratio, Reg 03h, an integer between 20 and 216- 1

Nfrac

is the fractional part, from 0.0 to 0.99999...,Nfrac=Reg 04h/224

is the reference path division ratio, Reg 02h

fxtal

is the frequency of the reference oscillator input

fpd

is the PD operating frequency, fxtal/R

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