Abstract: A compensation circuit for a resistance bridge corrects errors in the response of signal outputs thereof and has a voltage controlled current source across a power input and a ground reference providing a bridge excitation output current proportional to a fixed circuit reference voltage. A single resistor adjusts positive or negative values of the fixed part of the offset errors in the signal outputs response. Another resistor adjusts positive or negative slope of the temperature dependent part of the offset errors in the signal outputs response. A method compensates the offset errors with steps of energizing the bridge and measuring the output and resistance at two temperatures and at two pressures. The measurements are used to find correction resistances for variations in bridge offset, temperature and pressure response.

Abstract: An interface circuit for interfacing a semiconductor transducer sensor to a patient vital signs monitor is disclosed. In one embodiment, the interface circuit includes a power supply circuit that receives an excitation power signal generated by the patient monitor, and derives therefrom unregulated and regulated supply voltages for use by the electrical components on the interface circuit. Also generated by the power supply circuit is an appropriate sensor excitation signal for the semiconductor transducer. In another embodiment, the interface circuit further includes receiving circuitry for receiving a sensor output signal generated by the transducer sensor. A scaling circuit then scales that signal into a parameter signal that is proportional to the physiological condition detected by the sensor, and that is also proportional to the excitation power signal generated by the patient monitor.

Abstract: A filter for rezeroing an in-vivo pressure sensor is disclosed. The filter operates in a signal mode and a rezero mode. In the signal mode, the filter is a low pass filter which filters out noise. In the rezero mode, the filter is a low pass filter which filters out the dynamic components of an in-vivo pressure signal caused by the rezeroing of the pressure sensor. The filter is switchable between the signal and rezero modes. The filter is implemented by means of an active two pole RC filter with a Butterworth response. A circuit is provided to shorten the time in which the filter reaches its final response characteristic. Also disclosed is a method for processing an output from an in vivo pressure transducer, the output signal comprising noise, a mean pressure signal and a dynamic pressure signal.

Abstract: An apparatus and method for compensating for temperature dependent offset and fixed offset in a resistance bridge is disclosed. The apparatus comprises a resistance bridge, a compensation network and an instrumentation amplifier. The uncompensated output of the bridge is applied to the input of the instrumentation amplifier. The output of the compensation network is fed into the instrumentation amplifier to compensate for the temperature and offset dependent components of the bridge output. The output and resistance of the bridge are measured under conditions of constant pressure and temperature for different temperatures and pressures and the temperature coefficient of resistance, temperature coefficient of offset and temperature coefficient of sensitivity are calculated. These coefficients are used to select compensation network resistors.