1. A voltage controlled oscillator (VCO) with a symmetrical output comprising: a periodic signal generator having an input terminal for receiving an input voltage, and first and second output terminals for respectively providing a first signal and a second signal of a periodic differential output signal; and a logic gate having first and second input terminals respectively coupled to said first and second output terminals of said periodic signal generator, and an output terminal coupled to an output node, comprising: a first switching element having a first terminal coupled to a first power supply voltage terminal, a second terminal coupled to an output node providing an output signal of the VCO thereon, and a control terminal for receiving said first signal; a second switching element having a first terminal coupled to said first power supply voltage terminal, a second terminal coupled to said output node, and a control terminal for receiving said second signal; a third switching element having a first terminal coupled to said output node, a second terminal coupled to a second power supply voltage terminal, and first and second control terminals respectively receiving said first and second signals, said third switching element including first and second switching subelements serially coupled between said output node and said second power supply voltage terminal respectively responsive to said first and second signals; and a fourth switching element having a first terminal coupled to said output node, a second terminal coupled to said second power supply voltage terminal, and first and second control terminals respectively receiving said second and first signals, said fourth switching element including third and fourth switching subelements serially coupled between said output node and said second power supply voltage terminal respectively responsive to said second and first signals.