Philips Semiconductors
Product specification
1GHz low-voltage Fractional-N synthesizer
SA7025
Table 1. Function Table
Symbol
Bits
Function
Number of main divider cycles when prescaler modulus = 64*
Number of main divider cycles when prescaler modulus = 65*
NM1
12
8 if PR = “01”
4 if PR = “10”
NM2
NM3
PR
4 if PR = “10”
2
Number of main divider cycles when prescaler modulus = 72*
Prescaler type in use
PR = “01”: modulus 2 prescaler (64/65)
PR = “10”: modulus 3 prescaler (64/65/72)
NF
3
1
Fractional-N increment
FMOD
Fractional-N modulus selection flag
“1”: modulo 8
“0”: modulo 5
LONG
1
A word format selection flag
“0”: 24 bit A0 format
“1”: 32 bit A1 format
CN
CL
CK
EM
EA
SM
SA
NR
NA
8
2
Binary current setting factor for main charge pumps
Binary acceleration factor for proportional charge pump current
Binary acceleration factor for integral charge pump current
Main divider enable flag
4
1
1
Auxiliary divider enable flag
2
Reference select for main phase detector
Reference select for auxiliary phase detector
Reference divider ratio
2
12
12
Auxiliary divider ratio
Auxiliary prescaler mode:
PA = “0”: divide by 4
PA = “1”: divide by 1
PA
1
*Not including reset cycles and Fractional-N effects.
MAIN SELECT
SM = “00”
MAIN
SM = “01”
PHASE
DETECTOR
SM = “10”
SM = “11”
REFERENCE
DIVIDE BY NR
÷2
÷2
÷2
INPUT
AUXILIARY SELECT
SA = “11”
AUXILIARY
PHASE
SA = “10”
SA = “01”
SA = “00”
DETECTOR
SR00606
Figure 7. Reference Divider
Table 2. Prescaler Ratio
The total division ratio from prescaler to the phase detector may be expressed as:
if PR = “01”
if PR = “10”
N = (NM1 + 2) x 64 + NM2 x 65
N’ = (NM1 + 1) x 64 + (NM2 + 1) x 65 (*)
N = (NM1 + 2) x 64 + NM2 x 65 + (NM3 + 1) x 72
N’ = (NM1 + 1) x 64 + (NM2 + 1) x 65 + (NM3 + 1) x 72 (*)
(*) When the fractional accumulator overflows the prescaler ratio = 65 (64 + 1) and the total division ratio N’ = N + 1
12
1996 Aug 6
NXP [ NXP ]
