2.2 Gas or PM2.5 Detector

A current-to-voltage converter (usually a trans-impedance amplifier with low-leakage input) measures the photodiode current, with an optional second-stage voltage signal conditioner before analog-to-digital conversion.

This application typically uses a battery supply; the ultra-low-power MCU and its related analog modules contribute most to power consumption. This is especially true in a gas sensor node that must continuously monitor carbon dioxide gas concentration and generate an alarm if the concentration exceeds a given limit for a certain amount of time. The ultra-low power smart analog combos within lower-power FRAM MCUs benefits applications requiring continuous signal monitoring, such as gas detectors. Figure 3 shows a block diagram of a gas detector using the smart analog combo SAC-L3 configuration.