Philips Semiconductors
Product specification
1GHz low-voltage Fractional-N synthesizer
SA7025
MSB
LAST IN
WORD
D31
LSB
D0
FIRST IN
NM2
A1
0
NF
NM1
NM3
NM2
CN
D23
D0
NM2
A0
0
NF
NM1
NM3
NM2
PR = “01”
PR = “10”
B
1
0
0 0
0
0
0 0
CN
CK
CL
PR
C
1
0
0 1
NA
P
A
0
D
1
0
1 0
NR
SM
E
M
SA
F L
E M O
A O N
D G
E
1
1
1 1 0
0 0
T T
1
0
0
D23
ADDRESS BITS
TEST BITS
D0
SR00605
Figure 6. Serial Input Word Format
Current Settings
The SA7025 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 connected between the current
setting pin and V
SS
. The typical value R (current setting resistor)
can be calculated with the formula:
R
+
V
DDA
*
0.9
*
150
I
R
I
R
|I
PHA
|
+
8
@
I
RA
Main Output Charge Pumps and Fractional
Compensation Currents
The main charge pumps on pin 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 9 shows the waveforms for a typical case.
The current can be set to zero by connecting the corresponding pin
to V
DDA
.
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 RA at pin RA. The active charge pump current is typically:
1996 Aug 6
11
PHILIPS [ NXP SEMICONDUCTORS ]
