ACE9030
larger current. The charge pumps on PDI are only used in
Nominal Charge Pump Currents
speed-up and then drive the integrating capacitor Ci directly.
ThecontrolsignalsØUP andØDOWN aretheerrorsignalsfronthe
phase detector and have a duration proportional to the phase
error, the signal Fc is the Fractional-N compensation gating
pulse and has a fixed duration set by the crystal oscillator.
Shown in table 5, charge pump currents are set by the
resistors RSMA and RSC and by scaling coefficients loaded
from the serial bus. CN is an 8 bit number, L is 2 bit and K is
4 bit. Fractional-N compensation also depends on the instan-
taneous value ACC in the fractional accumulator, a 3 bit
number.
Pin
PDP
PDI
PDP
PDI
Charge pump
Main
Normal
Iprop(0) = CN x IRSMA/32
Off
Icomp(0) = ACC x IRSC/320
Off
Speed-up
Iprop(1) = 2L + 1 x Iprop(0)
Iint = K x Iprop(1)
Icomp(1) = 2L + 1 x Icomp(0)
Icomp(2) = K x Icomp(1)
no auxiliary speed-up
Maximum setting*
1·0 mA
Main
5 mA
12 µA
180 µA
512 µA
Fractional-N
Fractional-N
Auxiliary
PDA
Iauxil = 8 x IRSMA
* Larger values of current can be set by the programming numbers and the resistor values, but the circuit is not then guaranteed to give the
calculated current.
Table 5
Two Modulus Prescaler Control
The Main ACE9030 synthesiser is designed to operate
with the two-modulus prescaler section of the ACE9020. This
allows channels to be spaced at the comparison frequency
while keeping the clock rates within the range possible in
CMOS. ACE9030 can also be used with standard two-modu-
lus prescalers such as SP8715.
The prescaler will have two division ratios, R1 and R2,
selected by a Modulus Control signal and designed to switch
quicklyfromoneratiototheothersothatasequenceofR1and
R2 can be used to give the required total division. It is usual to
have R2 = R1 + 1 and to select R1 by setting Modulus Control
to the HIGH state and R2 by a LOW state.
standard prescalers from GEC-Plessey Semiconductors if
MODMP is used alone. Even if a prescaler with non-differen-
tial control input is used there could still be some benefit in
running a MODMN track on the circuit board beside the
MODMP track to partly cancel capacitive coupling to sensitive
nodes. Simplified waveforms are shown in figure 27.
Unlike many conventional synthesisers that use two
separate counters, to give both the total count, M, and the
portion for which the prescaler is at its higher ratio, A, there is
onlyonecounterintheACE9030forboththesefunctions.This
counter is loaded with the value N1, counts down to zero,
changes direction, counts up to N2, is again loaded with the
value N1 and changes direction to down, and so the cycle is
repeated indefinitely.
To reduce interference the Modulus Control output from
ACE9030isapairofdifferentialsignalsMODMPandMODMN
each with a limited voltage swing but still able to drive selected
...R1...
...R2 ...
PRESCALER RATIO
R1
R1 R2
R2 R1
FIM
FIMB
N1
N2
MODMP
MODMN
T
T
SET-UP
DELAY
COUNTER OUTPUT TO
PHASE COMPARATOR
N1 + N2
Fig. 27 Modulus Control Timing Diagram
28
MITEL [ MITEL NETWORKS CORPORATION ]
