S1T8825B

1.3GHZ DUAL PLL

10

FILTER SWITCH CONTROL (SW)

The operation mode of the SW terminal is set by bit “SW”.

SW control is useful for switching the time constant of the loop filter.

Output type of this terminal is an open drain output. High lock mode or normal lock mode can be used, taking

advantage of filter switch control (SW) with the charge pump output current.

When fast lock function can’t be used, normal lock mode is available.

CRYSTAL OSCILLATOR CIRCUIT (OSCI, OSCO) AND BUFFER OUT (BO)

External capacitors C1, C2, C3, and C4 are required to set the proper crystal’s load capacitance and oscillation

frequency as shown in figure 4. The value of the capacitors is dependent on the crystal chosen.

The BO (Pin9) outputs local oscillation signal with buffer amplifier.

This terminal (Pin9) can be applied to the 2nd mixer input

Figure 4.

Control Bits

Operation Mode

(SW and LPF example) The third order LPF

SW

CP1

CP2

00

0

Normal Lock Mode

00

1

01

0

01

1

10

0

High Lock Mode

10

1

11

0

11

1

CP1

SW

GND

R

R

R

OSCI

BO

OSCO

1000pF

C3

C2

C4

C1

2'nd MIX

or OPEN

2'nd MIX

or OPEN

Reference Oscillator

OSCI

OSCO

BO

1000pF

1000pF