AN1646, Noise Considerations for Integrated Pressure Sensors

The Integrated Pressure Sensors (IPS) have trimmed outputs, built-in temperature compensation and an amplified single-ended output which make them compatible with Analog to Digital converters (A/D's) on low cost micro-controllers. Although 8-bit A/D's are most common, higher resolution A/D's are becoming increasingly available. With these higher resolution A/D's, the noise that is inherent to piezo-resistive bridges becomes a design consideration. The two dominant types of noise in a piezo-resistive integrated pressure sensor are shot (white) noise and 1/f (flicker noise). Shot noise is the result of non-uniform flow of carriers across a junction and is independent of temperature. The second, 1/f, results from crystal defects and also due to wafer processing. This noise is proportional to the inverse of frequency and is more dominant at lower frequencies. Noise can also come from external circuits. In a sensor system, power supply, grounding and PCB layout is important and needs special consideration. The following discussion presents simple techniques for mitigating these noise signals, and achieving excellent results with high resolution A/D converters.