1. Introduction
Most microcontrollers now come with internal ADCs ranging from 10 to 12 bits. In general applications, how much does the bit depth of ADC conversion affect measurement errors? Is a 12-bit ADC enough? Below, we will discuss the impact of ADC bit depth on measurement errors through practical measurements.
2. Circuit Design
We designed a test circuit using the F030 microcontroller for testing. The input analog signal is sent to ADC channel 0 after passing through an RC filter. Two resistors separate the analog ground and power supply. A 3.3V voltage regulator chip is also set up on the circuit board. The PCB is designed to accommodate a one-minute board-making method.
AD\Test\2024\April\TestADCBit.PcbDoc
▲ Figure 1.2.1 Test Circuit Schematic 720
▲ Figure 1.2.2 Test Circuit PCBAfter one minute, we obtained the fabricated test circuit board. The circuit was made perfectly. Next, we will perform the soldering test.
3. Measurement Results
A total of 2000 data points were collected within the measured voltage range, and the relationship between voltage and ADC was plotted. It can be seen that when the ADC sampling bit depth is relatively small, the error caused by quantization is significant. Although this is the average of 512 data points, the error mainly comes from the AD quantization. However, as the bit depth increases, fluctuations caused by noise can also be observed in the data. At this point, the error caused by noise exceeds that caused by the conversion bit depth.
▲ Figure 1.3.1 Collected Data for Different Bit DepthsBy performing linear fitting of the microcontroller AD data and the voltage, and calculating the variance of the fitted voltage and actual voltage errors, it can be seen that as the ADC conversion bit depth varies from 1 to 12, the variance decreases sharply. However, the rate of decrease slows down, and once the bit depth exceeds 10 bits, the error remains basically unchanged. This is the data line plotted after taking the logarithm of the variance. It is clearer to see that when the ADC conversion bit depth exceeds 10, the data error mainly comes from the circuit noise. Therefore, for data conversion, higher ADC bit depth is no longer useful.
▲ Figure 1.3.2 Linear Fitting Errors Corresponding to Different ADC Bit Depths| Bits | Var |
|---|---|
| 1 | 0.2016750843417479 |
| 2 | 0.05153571814548405 |
| 3 | 0.01352796032514819 |
| 4 | 0.003468020713918683 |
| 5 | 0.0008517649509084311 |
| 6 | 0.00020580205442651296 |
| 7 | 5.001551736517359e-05 |
| 8 | 1.3009367147500475e-05 |
| 9 | 5.263557870607768e-06 |
| 10 | 4.309030498367149e-06 |
| 11 | 4.297694583457816e-06 |
| 12 | 4.314972044296696e-06 |
▲ Figure 1.3.3 Bit Depth and Logarithm of Error※ Conclusion ※
This article presents actual measurements on the impact of ADC conversion bit depth on measurement data accuracy. When the ADC conversion bit depth is less than 10 bits, the data error decreases exponentially as the bit depth increases. Once the bit depth exceeds 10 bits, in the case of ordinary single-sided boards, the error generated by noise in the circuit becomes the main component. In fact, the ADC conversion bit depth no longer plays a role in reducing measurement errors.
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