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Reliable high-temperature CMOS oscillators are required for clock or time-base generation in several applications including data acquisition for aerospace, automotive control, oil field instrumentation, and pulp and paper digesters. In this paper, we present low-complexity resistive and capacitive temperature-compensation techniques for CMOS relaxation oscillators. In such oscillators, the frequency of oscillation is a function of a resistor-capacitor product. The resistive compensation technique employs a recently proposed monolithic resistor with a given temperature coefficient (TC) that uses contacts to adjust the TC of the resistor. The capacitive compensation technique is based on using a varactor to adjust the value of the timing capacitance over temperature to compensate for the high-temperature junction leakage current and to keep the oscillation frequency relatively constant. A prototype oscillator based on the proposed techniques is implemented in a standard 0.13-μm CMOS process and reliably operates over 25 to 180 °C. Measured results show that over the temperature range of interest the compensated oscillator achieves a temperature coefficient of 108 ppm/°C. The oscillator along with its output drivers occupies 7200 μm2 (2.3 × to 114 × smaller than state-of-the-art designs) and consumes 428 μW from a 2.5 V supply. For supply variations between 2 and 3 V, the frequency variation is ±1.09%/V.