Concept first:
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VREF is the reference voltage of A/D, and it is the standard of A/D measurement voltage. Only when VREF has high precision can A/D conversion precision be guaranteed. Just like a ruler, if the scale is not accurate, the measurement will naturally be inaccurate. Some A/D chip VREF can be directly provided by the internal reference source, and the external circuit is simple, and some can input a higher-precision reference source externally.
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VREF[VOLTAGE REFERENCE]: refers to a voltage that can always be kept constant in a circuit regardless of load, power supply, temperature drift, time, etc.
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Vref refers to the maximum value of the input analog voltage, used to compare the input voltage, the effective range of AD input: 0-Vref, if it is a 10bit ADC,
Vref=5v, 2^10(1024):5v, then the resolution of the ADC The rate is 5/1024=0.00488v.
Another example is that the reference voltage you choose is 5v, and your ad is 12 bits, then when your input voltage is 5v, the display of your single-chip microcomputer should be 4095, if it is 0v input, the value inside the single-chip microcomputer is 0, The value of the middle point has a linear relationship, that is to say, if your input is m, the value of the single-chip microcomputer is 4096*m/5, so in turn, you can calculate your input if you know the value of the single-chip microcomputer! -
Capacitors of 4.7uF and 0.1uF must be connected between List itemVref and AGND, of which 0.1uF is close to the chip pins and 4.7uF is outside, which can prevent the crosstalk of chip digital noise.
Reference blog post:[https://blog.csdn.net/chenhuanqiangnihao/article/details/118156090?ops_request_misc=&request_id=&biz_id=102&utm_term=vref&utm_medium=distribute.pc_search_result.none-tas