Sensor output signal processing circuit apparatus and method of diagnostic signal generation and extraction

A sensor output signal processing circuit apparatus comprising:

• a sensor readout circuit configured to receive, when in use, a conditioned analogue sensor signal comprising a measurement offset and having a first cycle of a first duration;
• a diagnostic signal circuit comprising an amplitude modulator circuit and a signal generator circuit operably coupled to the amplitude modulator circuit, the signal generator circuit being configured to generate, when in use, an analogue diagnostic signal and the amplitude modulator circuit being configured to modulate the analogue diagnostic signal to provide a modulated analogue diagnostic signal to the sensor readout circuit;
• and
• a signal extraction circuit operably coupled to a digital output of the sensor readout circuit;
• wherein
• the sensor readout circuit is configured to amplify and combine the conditioned analogue sensor signal and the modulated analogue diagnostic signal and to provide at the digital output thereof a digital output signal comprising a digital representation of the combination of the amplified analogue conditioned sensor signal and the amplified modulated analogue diagnostic signal, a digital representation of an amplification offset, and a digital representation of the measurement offset;
• the signal extraction circuit is configured to digitally process, when in use, the digital output signal and to provide separately digital demodulated representations of the amplified conditioned analogue sensor signal and the analogue diagnostic signal in amplified form, both without the measurement and amplification offsets;
• and
• the amplitude modulator circuit is configured to alternate polarities of the analogue diagnostic signal so that the modulated analogue diagnostic signal has a second cycle of a second duration where the second duration is an even numbered multiple of the first duration.