Improved CMOS Vco Circuit to Decrease Temperature and Process Dependence
Original Publication Date: 1988-Mar-01
Included in the Prior Art Database: 2005-Feb-14
Fig. 1 shows the basic circuit of a CMOS source coupled voltage controlled oscillator. The output frequency of the circuit is basically dependent upon the bias current I0, the capacitor C and the gate-to- source voltage of the transistor T8 (or T9). The gate-to-source voltage of T8 is responsible for the high tolerance of the output frequency versus the process variations and the high dependence of the output frequency versus the temperature. This is related to the fact that the basic parameters of the MOS transistor (threshold voltage and device transconductance) are very dependent upon process and temperature. A significant improvement can be brought to the circuit by removing transistors T8 and T9 of Fig.