High accuracy analog signal measurement with ultra low power MCU

September 30, 2013 //By Alison Evans
High accuracy analog signal measurement with ultra low power MCU
Alison Evans, European Technical Marketing Avnet Memec looks at the numerous design considerations faced when optimizing a high precision analog design for low power consumption.

While identifying suitable customers in existing as well as new or emerging markets Avnet Memec analyzes the challenges that will be experienced by designers.  There are many design considerations when optimizing a high precision analog design for low power consumption.  

The solution we consider here with low power microcontrollers (MCU) assumes that the design aim is to achieve the best low noise precision for 16-bit to 24-bit applications focused on sensor and data acquisition.  Typical applications for sensors include thermocouple or thermopile sensors and bridge sensors such as pressure, strain, flow, AMR and ultrasonic sensors.  Of course, these applications can be used for general purpose analog inputs in data acquisition systems as well.  

All of the solutions in the design we consider here achieve 18-bit to 22-bit ENOB (noise free bit design) are notable for highest precision.  The solutions system partition for signal conditioning includes the frontend gain stage (usually amplifiers or instrumentation amplifiers), ADC and precision voltage excitation or voltage references for ratiometric design.

Table 1:
Intersil’s key mixed signal analog components for highest precision,
low noise design

Starting with the op-amp; biasing circuitry, input, output and compensation stages need to be examined.

The DC biasing circuitry for the op-amp must provide accurately determined and suitably regulated quiescent biasing currents at very low current levels. The current must be insensitive to changes in temperature, supply voltage and process tolerances. The configuration of the input stage will dictate whether the op-amp can be used in a single low voltage (1.2 V, or lower) supply application. Very low power supply operation using core devices is desirable (but not always possible). Using a Class B or AB output stage can reduce the quiescent power dissipation particularly in a leaky process.

Utilizing products with Rail to Rail common Mode input range but with the capability to drive a small output load can be desirable to achieve lower power consumption. But of course we

Design category: 

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