Philips Semiconductors

Product specification

SA7025

1GHz low-voltage Fractional-N synthesizer

1996 Aug 6

12

Table 1. Function Table

Symbol

Bits

Function

NM1

12

Number of main divider cycles when prescaler modulus = 64

*

NM2

8 if PR = “01”

4 if PR = “10”

Number of main divider cycles when prescaler modulus = 65

*

NM3

4 if PR = “10”

Number of main divider cycles when prescaler modulus = 72

*

PR

2

Prescaler type in use

PR = “01”: modulus 2 prescaler (64/65)

PR = “10”: modulus 3 prescaler (64/65/72)

NF

3

Fractional-N increment

FMOD

1

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

8

Binary current setting factor for main charge pumps

CL

2

Binary acceleration factor for proportional charge pump current

CK

4

Binary acceleration factor for integral charge pump current

EM

1

Main divider enable flag

EA

1

Auxiliary divider enable flag

SM

2

Reference select for main phase detector

SA

2

Reference select for auxiliary phase detector

NR

12

Reference divider ratio

NA

12

Auxiliary divider ratio

PA

1

Auxiliary prescaler mode:

PA = “0”: divide by 4

PA = “1”: divide by 1

SA = “11”

SA = “10”

SA = “01”

SA = “00”

SM = “11”

SM = “10”

SM = “01”

SM = “00”

MAIN SELECT

AUXILIARY SELECT

REFERENCE

INPUT

DIVIDE BY NR

÷2

MAIN

DETECTOR

PHASE

AUXILIARY

DETECTOR

PHASE

÷2

÷2

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”

N = (NM1 + 2) x 64 + NM2 x 65

N’ = (NM1 + 1) x 64 + (NM2 + 1) x 65 (*)

if PR = “10”

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