S1M8821/22/23

INTERGER RF/IF DUAL PLL

18

•

Powerdown mode operation

There are synchronous and asynchronous powerdown modes for S1M8821/22/23.

Synchronous powerdown mode occurs if R18 bit is LOW, N20 bit is HIGH and charge pump output is in high

impedance state. In the synchronous power down mode, the powerdown function is activated by the charge pump

to diminish unwanted frequency jumps. Asynchronous powerdown mode occurs if R18 bit is HIGH and N20 bit is

HIGH.

When the PLL goes to either synchronous or asynchronous powerdown mode, preamp becomes debiased, R & N

counters keeps their load conditions and the charge pump becomes high impedance state. The oscillator circuitry

function becomes disabled only when both IF and RF powerdown bits are activated, i.e. N20 HIGH.

The PLL returns to an active powerup mode when N20 bit becomes LOW(either in synchronous or asynchronous

modes).

Phase Detector and Charge pump Characteristics

Phase difference detection range : -2

π to +2π

When R16 = HIGH

R18

N20

Powerdown mode status

0

0

PLL active

1

0

PLL active, only charge pump high impedance

0

1

Synchronous powerdown

1

1

Asynchronous powerdown

fr

fp

LD

fr>fp

fr=fp

fr<fp

fr<fp

fr<fp

CPo