Motorola Corporation

Robert M Hess

Robert B Jarrett

Roy E Hunninghaus

Randall C Gray

Edward E Li

An electrical interface circuit (200), for use with a zirconium dioxide sensor (202), includes an input differential amplifier (208) having its inverting input coupled to the circuit input (204) to receive a sensor voltage relative to sensor ground potential, and having its output coupled to the circuit output (210) to produce an output voltage relative to circuit ground potential. Additionally a feedback differential amplifier (214) has its inverting input coupled to the circuit output (210), its non-inverting input coupled to sensor ground potential, and its output coupled to the non-inverting input of the input differential amplifier (208) so that voltage change at the circuit input due to change of sensor ground potential relative to circuit ground potential is substantially cancelled.

Electrical interface circuit

A detection scheme processes the output signal from a sensor so as to provide an ultimate output signal that is more noise resistant and that has a transition representative of a threshold crossing in the sensor signal. A key part of the detection scheme utilizes an integrated version of the sensor's output signal and compares it to two reference levels. These reference levels are selected to be near the opposite extremes of the amplitude excursions of the integrated sensor signal. Each time the reference levels are exceeded, a binary signal is latched to one of two levels (e.g. high, low), and is further processed to provide the ultimate output signal that is free of multiple, unwanted transitions in the presence of noise.

Threshold crossing detection with improved noise rejection

An improved comparator circuit of the type which includes first and second differential PNP transistors operating in conjunction with a current mirror circuit includes an additional dual collector PNP transistor. That is, while the reference voltage is applied to the base of one of the differential transistors, the input voltage to be compared with the reference voltage applied to the emitter of the dual collector's transistor which has a first collector coupled to the base of the other differential transistor. The second collector is coupled to the base of the additional transistor. In this manner, should the input voltage fall below the substrate voltage, the additional transistor will be reverse biased thus preventing the parasitic diode at the base of the second differential transistor from turning on.

Comparator with substrate injection protection

There is disclosed an ignition control circuit of the type which facilitates the storage of energy in an external inductive load during a dwell period and the release of the stored energy from the inductive load through a spark gap at the end of the dwell period. The circuit includes switch means for conducting current through the inductive load during the dwell period, and an integrated circuit for turning the switch means on during the dwell period and off at the end of the dwell period. The integrated circuit includes an output transistor for controlling the switch means, a current source for driving the output transistor, and control means for enabling the current source during the dwell period and disabling the current source at the end of the dwell period.

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Arlington Heights, IL, United States of America

Robert M Hess