INFICON PLO-10i Phase Lock Oscillator - Manual (Page 67)

PLO-10 PHASE LOCK OSCILLATOR
THEORY OF OPERATION 8-19
Frequency Error vs. Crystal Resistance
0.001
0.010
0.100
1.000
10.000
100.000
1000.000
10000.000
100000.000
10 16 25 40 63
100 158 251 398 631
1,000 1,585 2,512 3,981 6,310 10,000
Crystal Resistance (ohm)
Frequency Error (Hz)
Freq. Error due
to a 5 pfd
Freq. Error due
to a 2 pfd
capacitance
Freq. Error due
to a 1 pfd
capacitance
Figure 27 Frequency Error Due to Imperfect Capacitance Cancellation
8.9 CALCULATING CRYSTAL POWER
Crystal power can be calculated as follows:
Crystal power, P
cry
= i 2 * R
cry
Crystal current, i = V
oc
/( R
s
+ R
cry
)
Hence, P
cry
= i 2 * R
cry
= [V
oc
/( R
s
+ R
cry
)] 2 * R
cry
Where:
V
oc
= Open Circuit crystal drive voltage = 125 mV
R
s
= Crystal drive source resistance = 20 ohms
R
cry
= Crystal resistance value in ohms
Examples:
1.
Crystal Resistance = 80 ohms
P
cry, in watts
= [0.125/(20 + 80)] 2 * 80 = 1.25E -4 watts or 125 µW
3. Crystal Resistance = 4000 Ω
P
cry, in watts
= [0.125/(20 + 4000)] 2 * 4000 = 3.87E -6 watts or 3.87 µW