thandana
Junior Member level 1
Hi All,
I want to design a colpitts crystal oscillator with operating frequency of 4MHZ. This is the calculations that i have done, please check and advise.
I want to calculate the values of R1, R2, C1, C2, C3 and C4, see attachment.
I saw a guide saying C1 should be a value between (39 – 82)pF and C2 between (39 - 220)pF for good performance
Please can you check for me if the above calculation is correct, please
I want to design a colpitts crystal oscillator with operating frequency of 4MHZ. This is the calculations that i have done, please check and advise.
I want to calculate the values of R1, R2, C1, C2, C3 and C4, see attachment.
I have selected C1 = 68pF and C2 = 220pF.
I saw a guide saying C1 should be a value between (39 – 82)pF and C2 between (39 - 220)pF for good performance
Ve = 10% of Vcc
Vcc = 12V
therefore Ve = 10% of 12V
=1.2V
Since Vbe for silicon is approximately 0.6V
Vbe = Ve + Vbe
= 1.2 + 0.6
= 1.8V
Also Ie = Ib + Ic
since Ic > Ib
there Ie = Ic = 1,2mA
Beta = Ic/Ib = (1,2mA/12µA)=100
therefore R2 = Ve/Ie = 1,2/1,2mA = 1K
Rc = 12/1,2mA = 10KΩ
R1 = (Vcc -Vb)/10Ib = (12-1.8)/(10X12µA) = 85KΩ
R2 = Vb/10Ib = 1,8/(10X12µA) = 15KΩ
Please can you check for me if the above calculation is correct, please