What does the VDD pin in the crystal oscillator circuit ?
In crystal oscillator circuit, common symbols and explanations are as follows:
VDD:D=device. Denotes the meaning of the device, i.e. the operating voltage inside the device
VCC:C=circuit. Denotes the meaning of the circuit, that is, the voltage of the access circuit
VSS:S=series. Means public connection, usually referring to the voltage at the common ground end of a circuit
GND: Used as a voltage reference point in a crystal oscillator circuit
| pin | function |
| 1 | N/C or tri-state |
| 2 | ground |
| 3 | output |
| 4 | Vdd |
Generally speaking, VCC = analog power supply and VDD = digital power supply.
Some IC have both VDD pins and VCC pins, indicating that this device has its own
voltage conversion function.For digital circuits, VCC is the power supply voltage of the circuit,
VDD is the working voltage of the chip (usually VCC > VDD), and VSS is the ground point.
It can be seen from the above that for the input voltage end of active crystal oscillator,
the correct expression should be "VDD", that is, the power supply with rated voltage
indicated by pin connection specifications, such as 1.8V, 3.3V or 5V.