1.3GHZ DUAL PLL

S1T8825B

11

PROGRAMMABLE REFERENCE COUNTER

This block generates the reference frequency for the PLL.

The reference divider is composed of 12-bit reference divider and a half fixed divider

Sending certain data to the reference divider allows the setting of any of 6 to 8190 divisions (multiple of two)

.

R = R1

Division ratio: 2

× R = 2 × (3 to 4095) = 6 to 8190

Data is shifted in LSB first.

Example) A 21.25MHz X-tal oscillator is connected, and divided into 25kHz steps.

(Reference frequency is 12.5kHz)

21.25 MHz

÷ 12.5 kHz = 1700

1700 = 2

× R

Division

Ratio

R12

R11

R10

R9R8R7R6R5

R4R3R2R1

3

000000000011

4

000000000100

•

••••••••••••

4095

111111111111

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11

R12

GC2

"1"

GC1

"1"

LSB

MSB

Group Code

Division Ratio of the R counter, R

0

1

0

0

1

0

1

0

1

1

0

0

1

1

MSB

LSB