Differential variable capacitors and their applications

An integrated circuit for differential variable capacitors having a first terminal and a second terminal, comprising:

• an n-type substrate;
• a p-well region, disposed on the top surface of said n-type substrate;
• at least three p-type ion implant regions, each disposed on the top surface of said p-well region;
• a voltage control terminal, coupled to said p-type ion implant regions;
• a first gate on the p-well region connecting to the first terminal;
• and
• a second gate on the p-well region connecting to the second terminal, wherein said first gate and second gate are disposed symmetrically on opposite side of said voltage control terminal.

A voltage controlled oscillator (VCO) system having a first terminal and a second terminal comprising:

• a frequency tuning circuit containing a differential variable capacitor for receiving a predetermined tuning signal for altering capacitances of the differential variable capacitor, wherein the differential variable capacitor comprising:
• a semiconductor substrate;
• a deep-implant region, disposed on the top surface of said semiconductor substrate;
• at least three light-implant regions, each disposed on the top surface of said deep-implant region;
• a voltage control terminal connecting to said light-implant regions;
• a first gate on the deep-implant region coupling to the first terminal;
• a second gate on the deep-implant region coupling to the second terminal;
• and
• a core circuit coupled in parallel with the frequency tuning circuit for providing an oscillation mechanism, wherein circuit elements of the VCO system are symmetrically arranged between the first terminal and the second terminal.