ACE9030MSLASHIWSLASHFP2Q datasheet(27/39 Pages) MITEL

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ACE9030

TIME GATING

SET CURRENT

OVERFLOW

COMPENSATION

CHARGE PUMP

CHARGE TO

LOOP FILTER

(TO PRESCALER

MODULUS CONTROL)

COMPENSATION

DAC

ACCUMULATOR

MODULO-5 OR 8

FRACTION

COMPARISON

FREQUENCY

Ico

PROPORTIONAL

CHARGE PUMP

FRACTIONAL-N

COMPENSATION

CHARGE PUMP

(INTEGRAL)

FRACTIONAL-N

COMPENSATION

CHARGE PUMP

(PROPORTIONAL)

EXTERNAL,

PASSIVE

LOOP FILTER

Cp, Ri, Ci

INTEGRAL

CHARGE PUMP

PDI

PDP

To VCO

VDD

Icomp(0) =

ACC.Ico

Icomp(1) =

x2, 4, 8, 16

Icomp2 =

K.Icomp(1)

lint =

K.lprop(1)

DOWN

VDD

Icomp(0) =

CN.lbo

Iprop(1) =

x 2, 4, 8, 16

DOWN

VSS (GND)

Fig. 25 Fractional-N Add-On To Main Synthesiser

and so increment the total division.

To avoid loop modulation due to the accumulating phase

shift at the fractional frequency, a compensation charge must

also be driven onto the loop filter to track the accumulated

phase error so a current Icomp(0) is output on PDP for a fixed

short duration. Icomp(0) is given by Icomp(0) = ACC x Ico,

where ACC is the value of the phase accumulator and Ico is

a current set by a resistor on pin RSC such that Ico = I

RSC/320.

In a typical system the required value of Ico is between 1/10 and

3 of Ibo and thus the resistor on RSMA has a value between

one and three times the value of the resistor on RSC. As with

RSMA, the pin RSC does not need any decoupling and to

avoid all possibilities of oscillation the external capacitance

should be less than 5 pF. For a full description of this mode see

the later section “Detailed Operation of Fractional-N Mode”.

In fractional-N mode a zero fraction numerator, in both

5’s and

8’s mode, will force the accumulator to zero and not

simply leave it at an arbitrary fixed value. This feature makes

testing easier by setting the accumulator to a known state, but

is also useful in operation by stopping all compensation pulses

when none are needed. Similarly in 1/8’s mode if

4 ( and

4 )

or 1/2 fractions are set then the LSB or two LSB’s in the

accumulator will be forced to zero to relax the tolerance on the

compensation.

Main Synthesiser - Fractional-N Mode with Speed-up

In Fractional-N mode with Speed-up the normal compen-

sation current is increased by the same factor (2L+1) as the

main charge pump current to give Icomp(1), and at the same

time the integrating capacitor is also driven with a compensat-

ing charge by a current Icomp(2) set to Icomp(1) x K. This extra

compensation is included so that the loop will step to exactly

the desired frequency during the Speed-up phase and then be

on channel when normal Fractional-N begins.

Main Synthesiser Charge Pumps

The charge pumps for all modes are shown together in

figure 26. The charge pumps on pin PDP are used normally to

hold a channel and are also used in speed-up modes at a

Fig. 26 Main Synthesiser Charge Pumps

ACE9030M/IW/FP2Q Fiches technique(PDF) 27 Page - Mitel Networks Corporation

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