This block is an oscillator circuit used to provide an accurate 20 MHz clock signal.
It operates from a regulated 1.5 V supply voltage with a typical current consumption of 280uA at 20MHz.
The main feature of this block is its frequency stability across temperature and supply voltage variations. It achieves a frequency stability of better than +/- 1 % from its nominal value over the whole operating temperature range with a
constant supply voltage. Including a possible supply voltage variation of +/- 5 % the frequency deviation is smaller
than +/- 2 %.
This accuracy is achieved by temperature-compensating the comparator delay with a small PTAT current added to the constant charge current for the capacitors outputted by the bandgap reference. This current can be trimmed for evaluation purposes but is intended to be kept constant. By trimming a capacitor array at room temperature, the output frequency is adjusted to its desired value.