MAC7100CVF datasheet(16/48 Pages) MOTOROLA

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MAC7100 Microcontroller Family Hardware Specifications

MOTOROLA

PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE

Electrical Characteristics

3.8.2.1

Jitter Information

The basic functionality of the PLL is shown in Figure 3. With each transition of the clock fcmp, the deviation

from the reference clock fref is measured and input voltage to the VCO is adjusted accordingly. The adjustment

is done continuously with no abrupt changes in the clock output frequency. Noise, voltage, temperature and

other factors cause slight variations in the control loop resulting in a clock jitter. This jitter affects the real

minimum and maximum clock periods as illustrated in Figure 4. It is important to note that the pre-scaler used

by timers and serial modules will eliminate the effect of PLL jitter to a large extent.

Figure 4. Jitter Definitions

The relative deviation of tNOM is at its maximum for one clock period, and decreases towards zero for larger

number of clock periods (N). Thus, jitter is defined as:

For N

< 100, the following equation is a good fit for the maximum jitter:

Figure 5. Maximum Bus Clock Jitter Approximation

tMIN1

N–1

tNOM

tMAX1

tMIN(N)

tMAX(N)

()

max 1

tMAX N

()

NtNOM

⋅

---------------------

–1

tMIN N

()

NtNOM

⋅

---------------------

–





()

-------- j2

J(N)

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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