Why is the 32 kHz crystal oscillator used in RTC, instead of the 16 kHz?

Why is the 32 kHz crystal oscillator used in RTC, instead of the 16 kHz?

 

A 32 kHz "crystal" actually is a type of tuning fork. This is used because at these low frequencies it is much smaller than a standard AT cut crystal would be. Still, size is everything inside a wrist watch. 32 kHz was a tradeoff between size (higher freq = smaller) and circuit complexity (higher freq = more divider stages).

It has nothing to do with accuracy. A 1% error in a 10 MHz oscillator, a 10 kHz oscillator, and a 10 Hz oscillator will produce the exact same 1% error percentage when they are divided down to 1 Hz.

ak

 

He was not asking, he was telling you - he already had the link and the answer - he was asking you to read his link.

 

I think you are remembering the color burst crystal @ 3.579545 MHz. That was the 1960's TV technology. 32,768 kHz came from digital watches c. 1974

 

I need to get me some of them 1Hz crystals! I will make building clocks a piece of cake!

 

Just grow it by 2^15

 

Not National's best work.

ak

 

Not always you can take any xtal / oscillator depending what accuracy and lowed time stamp you want and more the (price performance ratio)
0.00000000001 second or 1 second or in between.

Picbuster

 

http://www.riana.com/electronics/docs/MM5369.pdf

 

Try this instead:

 

Sorry -- never heard of that one. Was it used in television sets?

 

Oh I see, it was a chip used in conjunction with the color burst crystal. I never knew that.

 

The 3.9545[Correction 3.579545] MHz crystal could be easily divided by a binary divider to obtain nearly 60 Hz (60.6606 Hz).




Factor(59660) = 2 x 2 x 5 x 19 x 157 and 59659 is prime. What divisor did you have in mind?
the closes divisors to 60.6606 Hz are 59009 and 59010.
Factor(59010) = 2 x 3 x 5 x 7 x 281 and 59009 is prime

 

The output frequency with a perfect crystal is 60.00008381 Hz. This translates into a steadily accumulating error of 7.241 seconds per day (fast), so the circuit is not nearly as accurate as a crystal oscillator based on something that is a decade or binary multiple of 60 Hz.

ak