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This paper presents a fully integrated programmable biomedical sensor interface chip dedicated to the processing of various types of biomedical signals. The chip, optimized for high power efficiency, contains a low noise amplifier, a tunable bandpass filter, a programmable gain stage, and a successive approximation register analog-to-digital converter. A novel balanced tunable pseudo-resistor is proposed to achieve low signal distortion and high dynamic range under low voltage operations. A 53 nW, 30 kHz relaxation oscillator is included on-chip for low power consumption and full integration. The design was fabricated in a 0.35 mum standard CMOS process and tested at 1 V supply. The analog front-end has measured frequency response from 4.5 mHz to 292 Hz, programmable gains from 45.6 dB to 60 dB, input referred noise of 2.5 muVrms in the amplifier bandwidth, a noise efficiency factor (NEF) of 3.26, and a low distortion of less than 0.6% with full voltage swing at the ADC input. The system consumes 445 nA in the 31 Hz narrowband mode for heart rate detection and 895 nA in the 292 Hz wideband mode for ECG recording.