for STM32F405RGT, for the ground pin of HSE crystal oscillator 's load capacitor ,should it connect to the AGND or DGND？ Because I use the ADC of the MCU，so i seperate the AGND(vssa) and DGND(vss).

[JieHong Mai]

I want the ADC of the MCU be more accurate.

I know the PLL belong to the power field of the VDDA .Thanks.

[Uwe Bonnes]

Connect to HSE load capacitors to DGND. But read the datasheet again. In my understanding, AGND and DGND need to be connected near the CPU.

[S.Ma]

My guess is connect the oscillator to the digital ground. If guidance is required, look at the corresponding Nucleo board schematic and layout.

Not signal integrity just tell you to minimize current loop length and area, this will tell where both analog and digital grounds will be joined.

ADC accuracy depends on monitoring Vdd, having good quality Vdda regulation, averaging adc results if it has white noise, etc...