[Table 1] Presence of AVREF Pin
[A-D input signal selection]
- The ideal input signal for A-D conversion is a complete DC signal without noise. To this end, it is important to input a band limited signal, and noise coming in through the input signal is limited using RC filters, in general.
If resistance value makes an effect to the input level, you can use only simple capacitors in some cases. The input signal for A-D conversion can be set according to the assigned pin. Usually, the last input signal is connected to the internal constant voltage power source (1.2V) without assigning to A-D input signal pin.
- Differential Non-linearity (DNL) characteristic includes a phenomenon that a value stands out abnormally at a specific location. Integral Non-linearity (INL) characteristic is a factor that causes a gap from the ideal slope due to the accumulated errors, and can be described as the difference between the maximum value (0xFFF) and an input signal approaching the reference voltage.
[Zero Input Offset compensation]
- The high precision A-D conversion has a Zero Offset characteristic that causes critical errors when measuring the micro-voltage.
For example, assuming that you measure the end-of-charge current, based on the power supply voltage of 2.8V, the A-D conversion result of 5mV is theoretically a small value of 0x007 and the ADC Zero Input Offset management is an important item.
If Zero Offset value is -6, the A-D conversion result of 5mV is 0x001 which is not a valid value. In particular, the minus Offset values causes the A-D converter to read all low level signals of mV units as 0x000, making it impossible to measure. Therefore, to improve the precision, manufacturers should provide users with information regarding the Input Offset characteristics and the users should correct the Offset value of the A-D conversion result.
An Offset value that can identify the minimum input signal must be determined to define the effective limit of minus Offset value.
[Figure 3] ADC Zero Offset Characteristics (Example: A96G174)
[Table 2] shows the memory location where each MCU stores the Input Offset value of the A-D converter. Before starting user program, read the Offset value of the MCU. And after A-D conversion, obtain a correct A-D conversion value by subtracting the Offset value from the read value of A-D conversion.
The Zero Offset Compensation is applied only when a low input voltage of 100mV or less is accurately measured. The reference voltage of the Zero Offset Compensation is the Internal Reference (VDD).
NOTE) This device is scheduled to support this feature later.
[Table 2] ADC Zero Offset Storage Location