Intel 82541PI Design Manual page 82

82541PI(ER) and 82562GZ(GX) Dual Footprint LOM Design Guide
where
Example 3.
Given: The measured averaged center frequency is 24.99963 MHz (or 24,999,630 Hertz).
FrequencyAccuracy ppm
Example 4.
Given: The measured averaged center frequency is 25.00027 MHz (or 25,000,270 Hertz).
FrequencyAccuracy ppm
Note: The following items should be noted for an ideal reference crystal on a typical printed circuit
board.
•
If the transmitter reference frequency is more than 8 ppm below the target frequency, then the
values for C1 and C2 are too big and they should be decreased. When tests are performed
across temperature, it may be acceptable for the center frequency deviation to be a little greater
than 8 ppm.
•
If the transmitter reference frequency is more than 8 ppm above the target frequency, then the
values for C1 and C2 are too small and they should be increased. When tests are performed
across temperature, it may be acceptable for the center frequency deviation to be a little greater
than 8 ppm.
74
FrequencyAccuracy ppm
x = Average measured frequency in Hertz and
y = Ideal reference frequency in Hertz
( )
(
(
x y
( )
= ------------------------------- -
( ⁄
y 1000000
(
24999630 25000000 –
= ----------------------------------------------------------
( ⁄
25000000 1000000
(
25000270 25000000 –
)
= ----------------------------------------------------------
( ⁄
25000000 1000000
)
–
)
)
= – 14.8ppm
)
)
= 10.8ppm
)
Application Note (AP-468)