17.8 A 190nW 33kHz RC oscillator with ±0.21% temperature stability and 4ppm long-term stability

In wireless networks with a low duty cycle, the radio is operational for only a small percentage of the time. A sleep timer is used to synchronize the data transmission and reception. The total system power is then limited by the sleep power and the sleep timer frequency stability. Low-frequency crystal oscillators are a common choice for sleep timers due to their excellent long-term stability, frequency stability over temperature, and very low power consumption. However, the external crystal cost and board area are undesired. If an integrated oscillator is used as an alternative, the frequency variation must be minimized so the sleep time can be maximized.