High accuracy analog signal measurement with ultra low power MCU: Page 2 of 5

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.
still need to consider maintaining the high precision, accuracy and keeping offsets low with high input impedance  is imperative while managing a high CMRR (Common Mode Rejection Ration) and PSRR (Power Supply Rejection Ratio). These are just some of the main considerations for the op-amp but there are of course a number of components required in a high precision signal chain one of the most important being the ADC.  Higher throughput requires higher power consumption.

Reducing Sample Rates will reduce power consumption, which can potentially reduce the precision capabilities of the circuit design.  With suitable conditioning and buffering an optimum performance can still be achieved while continuing to manage power efficiency effectively.

Choosing individual analog components including the ADC, op-amp, buffers and voltage regulators that work at lower supply voltages is a major consideration when optimizing your design for reduced power consumption.

If you require your design to work in a hand held application an obvious advantage here is to use batteries, which produce less noise than standard power supplies.

Immediately your analog signal path will have less interference from environmental and electrical disturbances.  Also use of differential signal conditioning where possible can reduce noise in the design and also increase the dynamic range prior to ADC conversion.

The combination of the Intersil ISL28134 in differential configuration with the ISL26102 makes for one of the best implementations of precision, low noise design common in bridge sensor and data acquisition applications.

The components chosen for the reference design are chopper stabilized op amplifiers, the ISL28134; and the Delta Sigma ADC, ISL26102/104.  The data acquisition solution shows 'DAQ on Stick' as an example.  The solution employs the techniques mentioned previously to achieve lowest noise design for precision applications. 

The 'DAQ on Stick' evaluation platform includes GUI software to select gain for various sensors including pressure, strain, flow, AMR and Ultrasonic sensors.  Included in the demo is a Strain Gauge sensor (using Vishay’s

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