Analog pattern classifier with flexible matching circuitry based on principal-axis-projection vector representation

An analog CMOS classifier circuit has been developed for pattern recognition based on a robust image representation algorithm called the Principal Axis Projection method [1]. The short-cut current in a CMOS inverter is modulated by a variety of capacitance coupling techniques, thus enabling real-time altering the functional form of the similarity evaluation. Not only the peak position and the peak height in the bell-shaped current-voltage characteristics but also the sharpness of the bell shape are made alterable for flexible pattern matching operation. Test circuits were designed and fabricated in a 0.6µm double-poly CMOS process. Handwritten pattern matching experiments were carried out and the flexible and adaptive matching capabilities of the circuit were demonstrated.