I've had good luck with TI's CDC913/925/937/949 programmable PLLs. (The middle digit is the number of PLLs, and the last digit is the number of outputs.)
I haven't tested them for phase noise, but for an NTP application all you need is long-term phase lock. They're fractional-N PLLs, so you can use deep divider ratios. They're I2C programmable and have onboard EEPROM so you can set a power-on configuration. They do require a +1.8V supply, which the Pi already has. Now, first of all, you're misreading the schematic. X2 is 19.2 MHz, not 19.5. So you need to multiply by 192/100 = 48/25. The onboard VCO can go up to 230 MHz, so the obvious way to do this is to use an input divisor of 5, a feedback divisor of 48 or 96 (thus a VCO frequency of 96 or 192 MHz), and an output divisor of 5 or 10. Any 2-pin crystal connection to an IC is a simple Pierce oscillator. There's an on-chip inverter, with a high-impedance feedback resistor to keep the duty cycle balanced. You want to disconnect the output pin XTALN, and feed the input XTALP with an AC-coupled waveform of about 1 V p-p. So use a capacative divider between the PLL output and ground to get the voltage right. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
