Intel 80C188EC User Manual page 149

CLOCK GENERATION AND POWER MANAGEMENT
(a) Series or Parallel Resonant Frequency
1
f = ------------------------ -
2π L C
1
The equation in Figure 5-4(b) yields the equivalent capacitance C
The desired operation frequency is the third overtone frequency marked on the crystal. Optimiz-
ing equations for the above three criteria yields Table 5-1. This table shows suggested standard
inductor values for various processor frequencies. The equivalent capacitance is about 15 pF.
Table 5-1. Suggested Values for Inductor L
CLKOUT
Frequency (MHz)
13.04
16
20
5-4
1
Figure 5-4. Equations for Crystal Calculations
Third-Overtone Crystal
Frequency (MHz)
26.08
(b) Equivalent Capacitance
ω
2
C C L
1 x2
C = -----------------------------------------------------------
eq
2
ω
C
1
at the operation frequency.
eq
in Third Overtone Oscillator Circuit
1
32
40
– C – C
1 1 x2
L – 1
1
Inductor L
1
Values (µH)
6.8, 8.2, 10.0
3.9, 4.7, 5.6
2.2, 2.7, 3.3