System, method, and apparatus for detecting air in a fluid line using active rectification

A system for detecting air, the system comprising:

• a transmitter configured to transduce a driver signal to ultrasonic vibrations;
• a receiver configured to receive the ultrasonic vibrations and transduce the ultrasonic vibrations to provide a receiver signal;
• an air-detection circuit in operative communication with the receiver to process the receiver signal to generate a processed signal corresponding to detected air, the air-detection circuit comprising at least one active-rectifying element configured to actively rectify the receiver signal to provide the processed signal;
• a first conductive path to provide a first polarity of the receiver signal from the receiver;
• a second conductive path to provide a second polarity of the receiver signal from the receiver;
• a first switch electrically coupled to the first and second conductive paths, the first switch configured to switch a first switch output to between the first and second polarities of the receiver signal, the first switch defining the at least one active-rectifying element;
• a second switch electrically coupled to the first and second conductive paths, the second switch configured to switch a second switch output to between the first and second polarities of the receiver signal;
• a first amplifier having a positive input and a negative input, wherein the positive input is coupled to the first switch output and the negative input is coupled to the second switch output, wherein the first amplifier provides a first amplifier output in accordance with the positive and negative inputs;
• a first filter electrically coupled to the first amplifier output of the first amplifier to provide a first filter output;
• a third switch electrically coupled to the first and second conductive paths, the third switch configured to switch a third switch output to between the first and second polarities of the receiver signal;
• a fourth switch electrically coupled to the first and second conductive paths, the fourth switch configured to switch a fourth switch output to between the first and second polarities of the receiver signal;
• a second amplifier having a positive input and a negative input, wherein the positive input of the second amplifier is coupled to the third switch output and the negative input of the second amplifier is coupled to the fourth switch output, wherein the second amplifier provides a second amplifier output in accordance with the positive and negative inputs;
• and
• a second filter coupled to the second amplifier to provide a second filter output.