Dual mode relaxation oscillator generating a clock signal operating at a frequency substantially same in both first and second power modes

A microcontroller having a dual mode relax oscillator that is trimmable. In one embodiment, the present invention provides a relaxation oscillator circuit comprising two current sources for establishing a reference voltage for use in causing the relaxation oscillator circuit to operate in two power modes, and a control coupled to both current sources for switching between power modes. In one embodiment, one power mode is a low power mode for standard operation of the microcontroller and one power mode is a very low power mode for use in a sleep mode. In one embodiment, the relaxation oscillator circuit further comprises digitally trimmable components operable to control a current charging a capacitor of the relaxation oscillator circuit to account for process variation in the capacitor, wherein the current is for controlling a frequency of the microcontroller.