This low power precision gas sensor circuit operates in an oxygen level range of 0% to 30%, with a nominal output of 1V in normal atmospheric oxygen concentrations (20.9%) when the gas sensor has been fully initialized. Total active power consumption is less than 2.1μA on a single rail supply.
Since this gas sensor produces 100μA in a normal oxygen environment and requires a 100Ω load resistor, the resulting input signal is typically around 10mV. The LTC2063’s rail-to-rail input means no additional DC level shifting is necessary, all the way down to very low oxygen concentrations.
Due to the extremely low input offset voltage of the LTC2063, which is 1μV typically and 5μV maximum, it is possible to gain up the mV-scale input signal substantially without introducing significant error. In the configuration shown in Figure 9, with a non-inverting gain of 101V/V, the worst-case input offset results in a maximum of 0.5mV offset on the 1V output, or 0.05% error.
Although the 100kΩ resistor in series with the gas sensor does not strictly have the same precision requirement as the 10MΩ and 100kΩ resistors that set the gain, it is important to use a similar resistor at both input terminals. This helps to minimize additional offset voltage at the inputs due to thermocouple effects, hence the similar 0.1% precision requirement.
Tools & Simulations
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