Methods and circuits for CMOS relaxation oscillators are disclosed. A single capacitive element, a single current source and a switching network are utilized. A switching network of the oscillator allows both nodes of the capacitive element to rise and fall between a positive and a negative voltage with respect to ground supply, without causing leakage to substrate or risk of latch-up, i.e. the inadvertent creation of a low-impedance path. The oscillator requires minimum silicon area, has an improved duty cycle, is particular useful for implementing lower frequency clocks and is enabled for smaller technology nodes, lower than 250 nm, due to lower supply voltage.