qzp100k vs qzs100k
Hi Looking at the circuit
Why we usually add another two addtional capacitors connect to the two terminals
of a crystal ? And how we choose the value of the two capcacitors ?We also could see in the pic that there is a very large resistor(1 mega Ohm)in parallel with the crystal,what's it used for?
I checked the model of crystal,i found something very interesting as below:
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* 100khz frequency standard, DT cut, parallel resonant, Q=20000
* calibration capacitance = 5pf
.subckt QZP100K 1 2
*
lqz 1 11 lmod 588.873289
.model lmod ind(tc2=3.5e-8)
cs 11 12 4.30423941e-015
rqz 12 2 18.5k
cp 1 2 1.72169576e-012
.ends
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* 100khz frequency standard, DT cut, series resonant, Q=20000
.subckt QZS100K 1 2
*
lqz 1 11 lmod 588.873289
.model lmod ind(tc2=3.5e-8)
cs 11 12 4.30148495e-015
rqz 12 2 18.5k
cp 1 2 1.72059398e-012
.ends
o,both the frequency of the two crystal is 100k,but what's the differences?I got confused!