Capacitor cells are provided. A first PMOS transistor is coupled between a power supply and a first node, and has a gate connected to a second node. A first NMOS transistor is coupled between a ground and the second node, and has a gate connected to the first node. A second PMOS transistor is coupled between the second node and the power supply, and has a gate connected to the second node. A second NMOS transistor is coupled between the first node and the ground, a gate connected to the first node, and has a gate connected to the first node. Sources of the first and second PMOS transistors share a P+ doped region in N-type well region, and the first PMOS transistor is disposed between the second PMOS transistor and the first and second NMOS transistors.