A Novel Capacitor Bank for Linearized and Wide-band VCO

A novel capacitor bank is proposed to implement a wide-band CMOS voltage-controlled oscillator(V CO) with linearized tuning characteristics. Taking advantage of the Ohms law, the tuning voltage is replaced by the product of the current and resistance, which provides one more freedom degree for tuning than the conventional V CO. This novel voltage equivalent capacitance array(V ECA) is clearly different from that of the conventional V CO, which is made up of only a group of varactors, a resistance array and a current source array. The resistance array and the current source array are controlled by four-bits digital signals which provide a group of bias voltages on varactors that can be equivalent to a capacitor array. Using this method, the capacitances can be set accurately and conveniently to adjust the frequency for the linearized coarse tuning. For the fine tuning, an analog control voltage is added to the bias voltage on varactors by using current superposition technology. Simulation results show that the tuning gain(KV CO) curves of the V CO is in little difference as the different digital signals vary, KV CO is in the range from −214 to −137MHz/V across the tuning range of 5 − 5.85GHz, and the frequency step is 166MHz. The proposed V CO has a better coarse tuning characteristic compared against the conventional V CO while dissipating 4.43mA from a 1.8V supply. Key–Words: voltage-controlled oscillator(V CO), wideband, linearized, capacitor bank