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Summary Two ultralow power CMOS full‐wave precision rectifiers aimed at analog signal processing in implantable medical devices are presented. The rectifiers require no diodes and utilize a single or two transconductors (operational transconductance amplifier [OTA]) as the active element, to reduce power consumption to a minimum. First, a voltage‐to‐current rectifier consuming only a 120‐nA supply current is presented and later is used to estimate the average AC amplitude of a piezoelectric accelerometer output (0.5–15‐Hz bandwidth) in an adaptive pacemaker. This rectifier is based on a linearized transconductor and a comparator to toggle the output current sign. Then, a novel voltage rectifier consuming less than 10 nA is presented based on a single nanopower OTA and a pass transistor and later is utilized in a pacemaker's cardiac sensing channel (60–200‐Hz bandwidth) circuit, incorporating the rectifier to detect positive and negative voltage signal spikes. Both rectifiers were designed in a 0.6‐μm CMOS technology, fabricated, and tested, and the measurement results closely fit the expected performance.