AN838 Datasheet, PDF (2/4 Pages) Silicon Laboratories – NANOPOWER CIRCUIT DESIGN IN LOW-FREQUENCY SENSOR APPLICATIONS

AN838
Figure 2. 4OX(2) O2 Sensor Transfer Curve
2.1. Circuit Implementation
The City Technology O2 sensor used in this circuit is a 4OX (2) O2 sensor and its accompanying transfer curve
shown in Figure 2. This sensor generates an output current proportional to oxygen gas concentration. Some
important specifications and attributes of this O2 sensor are:
Output signal: 100 µA(typ) in air (21% O2 – safe)
Output signal: 85 µA(typ) in air (18% O2 – unsafe)
Response time: ? 15s
Recommended resistive load: 100?, ±1% (for specified accuracy)
Lifetime: 2 years
Self-powered and self-contained
With a 10 mV signal voltage (~21% O2 concentration) applied to the op amp’s non-inverting input and a circuit gain
of 101, a 1 V-full scale voltage is generated. This output voltage can be applied to the input of an ADC to process
digitally the signal voltage. With an op amp exhibiting a 4-kHz gain-bandwidth product, the circuit’s closed-loop
bandwidth is ~40 Hz as shown in Figure 3.
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Rev. 1.0