Patent ID: 7355539
Filing Date: 2008-04-08
Classification: A61B,H03M

Abstract:
1. A pulse oximeter circuit comprising: a multi-bit sigma-delta modulator having an input adapted to receive a first analog signal representative of received red light and a second analog signal representative of received infrared light through a single path, the multi-bit sigma-delta modulator being configured to produce a digital output signal; and a feedback circuit configured to receive the digital output signal of the multi-bit sigma-delta modulator and generate a pulse width modulated signal (PWM), the PWM signal being directed to a first switching circuit and a D flip-flop, the first switching circuit providing a first or second reference voltage as a feedback signal to the multi-bit sigma-delta modulator, the D flip-flop generating a sample and hold signal, the sample and hold signal controlling a second switching circuit coupled to the input of the multi-bit sigma-delta modulator, the second switching circuit being configured to direct the first and second analog signals to an inverting input of the multi-bit sigma-delta during a sampling period.