trashbox
Advanced Member level 4
real time clock crystal capacitor
Hi all,
Regards to the 32.768KHz crystall oscillation circuit design for Real-time clock(RTC), some papers use tuning capacitors for frequency trimming such as the red capacitor Cx in the attachment. However, 32.768KHz crystal generally has a very small motional capacitor(Cs=2f~5f farad) and load capacitors C1 and C2 are about 10p~20p.So that the nominal frequency is mostly determined by Cs and Ls, which means if I want to tune frequency from 32.764Khz to 32.768Khz, I have to add about 8p farad as Cx.
Is this trimming technology reasonable or popular for crystal design for RTC? How can I get a precise 32.768Khz nominal frequency for RTC? Thanks in advance!
Regards,
Trashbox
Hi all,
Regards to the 32.768KHz crystall oscillation circuit design for Real-time clock(RTC), some papers use tuning capacitors for frequency trimming such as the red capacitor Cx in the attachment. However, 32.768KHz crystal generally has a very small motional capacitor(Cs=2f~5f farad) and load capacitors C1 and C2 are about 10p~20p.So that the nominal frequency is mostly determined by Cs and Ls, which means if I want to tune frequency from 32.764Khz to 32.768Khz, I have to add about 8p farad as Cx.
Is this trimming technology reasonable or popular for crystal design for RTC? How can I get a precise 32.768Khz nominal frequency for RTC? Thanks in advance!
Regards,
Trashbox