The Oscillator
PSØ21 offers 3 possibilities to add a reference clock:
- Internal oscillator driver for 32 kHz Oscillator
- Internal oscillator driver for high-speed reference 2 - 5 MHz
- External reference input
When working in measurement range 2 (recommended) the high-speed clock is preferred. It is used
- as predivider for the TDC measuring unit
- and for setting the cycle time
Principally we recommend using the clock driver of the PSØ21 with an external resonator or quartz. The clock is used as predivider for the TDC measuring unit. Its quality has direct influence on the quality of the measurement result. Low jitter and short-time stability are the important properties. When using the microcontroller's clock additional noise making the measurement quality worse is propable.
The quality needed for the resonant circuit is about 500 - 1000. From there it is sufficient to use a ceramic resonator. A quartz oscillator is not necessary, it produces no better results and has a longer settling time. |
