Do I need an crystal Oscillator?

[Ala]

..

[dbgarasiya]

you can use internal clock

[Ala]

Dear Dbarasiya

do you mean I don't not need to add a 8MHz crystal oscillator in my PCB?

[berendi]

The external crystal is needed only for USB, or when some timing task requires better accuracy than HSI.

E.g. as an asynchronous UART requires 5% accuracy, it might not work reliably in extreme temperatures.

[berendi]

Check the electrical characteristics chapter in the reference manual, both for ADC and the HSI internal oscillator. If they are adequate for your need, then no external components are needed apart from the decoupling capacitors.

Also read AN2834 How to get the best ADC accuracy in STM32 microcontrollers

[dbgarasiya]

hope you understand what i means as @berendi​  has explained

[dbgarasiya]

Best of luck

[S.Ma]

The internal frequency HSI has some tolerances across chips, temperature etc... you will get a min-max range from this.

Now check if all your peripherals are ok with this.

Using USB? Need probably HSE

Using high speed UART? Need probably HSE

Using RTC? Need probably 32.768kHz HSI

[Ala]

Dear .

so if I need UART, then I should add a 8MHz crystal oscillator, right?

[berendi]

Only if it would be used in a freezer, oven, or outdoors (i.e. outside the -10...85 °C range), and the usart speed is above 500 kbaud.