Calculating crystal power, Calculating, Crystal – INFICON PLO-10i Phase Lock Oscillator User Manual
Page 67: Power -19, Igure, Requency, Rror, Ue to, Mperfect, Apacitance
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