Digitally controlled oscillator design with a variable capacitance XOR gate

Digitally Controlled Oscillator (DCO) designs using three transistors XNOR gates as variable capacitance load are presented in this study. Two different design approaches for five- and seven-stage DCOs were reported. Output frequencies were controlled digitally with digital bits applied to delay cells. Five-bit controlled DCO using delay cell-I showed frequency and power variation of 1.5335-2.0526 GHz and 2.5906-2.4271 mW, respectively, by varying control word 00000-11111. Moreover, seven-bit controlled DCO showed frequency and power consumption variation of 1.0890-1.4764 GHz and 3.6268-3.3979 mW, respectively, with varying control word 0000000-1111111. Further, five-bit controlled DCO with delay cell-II showed frequency and power variation of 0.77891-1.3840 GHz and 6.5225-6.0320 mW, respectively, with control word variations 00000-11111. Seven-bit DCO showed frequency of 0.58322-1.0431GHz and power consumption of 9.006-8.3199 mW with control word variation 0000000-1111111. Power consumption, output frequency and Figure of Merit (FoM) of proposed circuits were compared with earlier reported circuits and the present approaches showed significant improvements.

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