Passive infrared sensor apparatus and method with DC offset compensation

A passive infrared (PIR) sensor apparatus comprising:

• a PIR sensor that generates a sensor signal;
• an amplifier, dc-coupled to the PIR sensor, that amplifies the sensor signal;
• and
• a circuit that compensates for dc offset in the sensor signal;
• wherein the circuit includes a detector that detects dc offset in the sensor signal and a controller that controls the amplifier based on the detected dc offset to reduce dc offset in the amplified sensor signal;
• wherein the controller and the detector are implemented by processes executed by a microprocessor, the microprocessor being programmed to detect dc offset in the amplified sensor signal, and generate a control signal to control the amplifier in response to detection of dc offset;
• wherein the amplifier includes a differential amplifier, the differential amplifier having a first input that receives the sensor signal and a second input that receives a reference voltage, and wherein the control signal generated by the processor adjusts the reference voltage received by the second input of the differential amplifier to cancel at least a portion of the dc offset in the sensor signal;
• and
• wherein the PIR sensor further comprises a resistor-capacitor circuit that sets the reference voltage, wherein the control signal charges a capacitor in the resistor-capacitor circuit at a duty cycle selected to adjust the reference voltage to cancel at least a portion of the dc offset in the sensor signal.

A method for processing a passive infrared (PIR) sensor signal comprising:

• dc coupling a sensor signal from a PIR sensor to an amplifier having a first input that receives the sensor signal and a second input that receives a reference voltage;
• amplifying the sensor signal with the amplifier;
• and
• compensating for dc offset in the sensor signal by adjusting the reference voltage to cancel at least a portion of the dc offset in the sensor signal in incremental steps until the dc offset in the sensor signal is canceled to an acceptable level.

A method for processing a passive infrared (PIR) sensor signal comprising:

• dc coupling a sensor signal from a PIR sensor to a differential amplifier having a first input that receives the sensor signal and a second input that receives a reference voltage;
• detecting dc offset in the sensor signal;
• amplifying the sensor signal with the amplifier;
• and
• compensating for dc offset in the sensor signal by controlling the amplifier based on the detected dc offset to reduce dc offset in the amplified sensor signal;
• wherein detecting the level of the dc offset and controlling the amplifier are executed by a processor, the processor receiving the amplified sensor signal from the amplifier to detect the level of dc offset and generating a control signal to control the amplifier;
• wherein the control signal generated by the processor is applied to adjust the reference voltage received by the second input of the differential amplifier and thereby canceling at least a portion of the dc offset in the sensor signal;
• and
• wherein the amplifier is coupled to a resistor-capacitor circuit that sets the reference voltage, the method further comprising charging a capacitor in the resistor-capacitor circuit at a duty cycle selected to adjust the reference voltage to cancel at least a portion of the dc offset in the sensor signal.

A passive infrared (PIR) sensor apparatus comprising:

• a PIR sensor that generates a sensor signal;
• an amplifier that amplifies the sensor signal to produce an amplified sensor signal, the amplifier being dc-coupled to an output of the PIR sensor to receive the sensor signal, wherein the amplifier includes a differential amplifier having a first input that receives the sensor signal and a second input that receives a reference voltage;
• a resistor-capacitor circuit that sets the reference voltage received by the second input of the amplifier;
• and
• a detector that detects a level of the dc offset in the sensor signal;
• and
• a controller that charges a capacitor in the resistor-capacitor circuit at a duty cycle selected to adjust the reference voltage to compensate for the dc offset in the sensor signal.