UMA1005T Philips Semiconductors (Acquired by NXP), UMA1005T Datasheet - Page 10

• Manufacturer Part Number: UMA1005T
• Description: Dual Low-power Frequency Synthesizer
• Manufacturer: Philips Semiconductors (Acquired by NXP)

Philips Semiconductors
The loading of the work registers NM1, NM2, NM3, NM4
and PR is synchronized with the state of the main counter,
to avoid extra phase disturbance when switching over to
another main divider ratio as is explained in Section “Serial
programming input”.
At the completion of a main divider cycle, a main divider
output pulse is generated which will drive the main phase
comparator. Also the fractional accumulator is
incremented with NF. The accumulator works modulo Q.
Q is preset by the serial control bit FMOD to 8 when
FMOD = 1. Each time the accumulator overflows, the
feedback to the prescaler will select one cycle using
prescaler ratio R2 instead of R1.
As shown above, this will increase the overall division ratio
by 1 if R2 = R1 + 1. The mean division ratio over Q main
divider cycles will then be:
Programming a fraction means the prescaler with main
divider will divide by N or N + 1.
The output of the main divider will be modulated with a
fractional phase ripple. This phase ripple is proportional to
the contents of the fractional accumulator FRD, which is
used for fractional current compensation.
Phase detectors (Fig.6)
The auxiliary and main phase detectors are a 2 D-type
flip-flop phase and frequency detector. The flip-flops are
set by the negative edges of output signals of the dividers.
The reset inputs are activated when both flip-flops have
been set and when the reset enable signal is active (LOW).
Around zero phase error this has the effect of delaying the
reset for 1 reference input cycle. This avoids non-linearity
or dead band around zero phase error. The flip-flops drive
on-chip charge pumps. A pull-up current from the charge
pump indicates that the VCO frequency shall be increased
while a pull-down pulse indicates that the VCO frequency
shall be decreased.
Current settings
The UMA1005T has 3 current setting pins RA, RN and RF.
The active charge pump currents and the fractional
compensation currents are linearly dependent on the
current in the current setting pins. This current I
set by an external resistor to be connected between the
current setting pin (pin 9) and V
(current setting resistor) can be calculated with the
November 1994
Dual low-power frequency synthesizer
NQ
SS
=
. The typical value for R
N
+
NF
------- -
Q
R
can be
10
equation:
The current can be set to zero by connecting the
corresponding pin to V
Auxiliary output charge pumps
The auxiliary charge pumps on pin PHA are driven by the
auxiliary phase detector and the current value is
determined by the external resistor (R
active charge pump current is typically: |I
Main output charge pumps and fractional
compensation currents
The main charge pumps on pins PHP and PHI are driven
by the main phase detector and the current value is
determined by the current at pin RN and via a number of
DACs which are driven by registers of the serial input. The
fractional compensation current is determined by the
current at pin RF, the contents of the fractional
accumulator FRD and a number of DACs driven by
registers from the serial input. The timing for the fractional
compensation is derived from the reference divider. The
current is on during 1 input reference cycle before and
1 cycle after the output signal to the phase comparator.
Figure 7 shows the waveforms for a typical case.
When the serial input A word is loaded, the output circuits
are in the ‘speed-up mode’ as long as the STROBE is
HIGH, else the ‘normal mode’ is active.
N
In the ‘normal mode’ the current output at PHP is:
I
Where:
In ‘normal mode’ the current at output PHI is zero.
R
I
PHP(N)
I
comp10
pump10
ORMAL MODE
=
------------------------------------------------------------ -
V
= I
DDA
=
pump10
=
FRD I
---------------------------
CN I
----------------------- -
–
0.5
128
29
I
+ I
R
RN
comp10
RF
–
237 I
; charge pump current.
; fractional compensation current.
DDA
.
.
R
Preliminary specification
ext
UMA1005T
) at pin RA. The
PHA
| = 8
I
RA
.