High accuracy analog signal measurement with ultra low power MCU: Page 4 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.
bridge sensor and data acquisition applications.  

Normally, the data acquisition system designer would be concerned with the chopping frequencies of the two ICs beating together, and would need to synchronize the chopping clock frequencies, or add extra filtering to remove the spurious outputs from the op. amp.  None of this complexity is necessary with the ISL28134.  A patented filter design reduces the chopping frequency spurious outputs to below the output noise level.

Figure 2:
The plot shows the 1/f corner for the ISL28134 at the
design parameter of 0.005 Hz

Now let's explore possibilities for data acquisition with low power microcontrollers. In order to achieve low power consumption with microcontrollers, techniques can be applied to periodically sample the sensor or data acquisition inputs. The newer microcontrollers have new provisions to allow for lower power sampling modes for peripheral devices to operate while the microcontroller is in lower power status (see Table 2).

Modern microcontrollers have additional functions to allow various low power operation modes for external circuits while the microcontroller operates in lowest power modes; for example 0.6 uA of stop or standby current or if single step data transfer is used as low as 45 uA/MHz. Hence this sets the stage to develop periodic sampling techniques of higher power analog frontend components to reduce power consumption between active and standby modes. For example, the ISL28134 can be left in active mode as low as 1.7 mW (at 2.5 V) while the ISL26102 is at 10 μW in standby mode. This technique would allow for a faster and safer response for sensor sampling at lowest power levels and routines can be developed in conjunction of the microcontrollers for independent peripheral operations whilst in lowest power modes.

Table 2:
Examples of new modern functions of low power microcontrollers

Combining the low-power capabilities of the Renesas RL78 MCUs and Energy Micro’s Ultra Low Power EFM32 with Intersil’s high-precision analog expertise provides

Design category: 

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