For battery-powered devices, one of the major design challenges is the reduction of power consumption in all functional blocks. An oscillator, a common functional block in many designs, can easily consume anywhere from a few microamps to a milliamp or more. The circuit shown uses a MAX919 to create an ultra-low-power oscillator for designs where the accuracy of the oscillation frequency is not critical (see the figure). The MAX919 is a single comparator with 0.4-µA power consumption.
R1 and R2 provide a reference voltage to the comparator. R3 is used to increase the threshold of the comparator. R4 and C1 are the main components that determine the frequency of the output signal. The table gives the output frequency for particular values of C1 as well as the resulting power consumption. The useful power-supply voltage ranges from 1.8 to 5.5 V. Since the MAX919 is a CMOS device, the logic-high and logic-low output voltages are nearly rail-to-rail.