A near-infrared heart rate sensor IC with very low cutoff frequency using current steering technique

In this paper, a near-infrared (NIR) heart-rate sensor IC, which will be used for portable biomedical application, was designed. This sensor consists of a current-to-voltage (I-V) converter, sample-and-hold (S/H) circuit, continuous time low-pass filter (CT-LPF), comparator and clock generation circuitry. Both switched-capacitor and current steering technique are used. The current steering technique is employed in the design of the CT-LPF due to the very low cutoff frequency requirement. As a result, only 20pF and 38pF capacitors are used to implement a 2^nd order filter with cutoff frequency of 18Hz. The circuit consumes 4.2mW when operating from a 3-V battery and occupies a core area of 0.46mm². The design was fabricated using 0.35μm CMOS technology and simulation results show that the circuit works properly.