[LETTER] 5-MHz Pseudo-differential Current-mode CMOS Relaxation VCO with Temperature Stability of 41.8 ppm/°C

This letter presents a pseudo-differential current-mode relaxation voltage-controlled oscillator for small form factor applications. A pseudo-differential current-mode comparator with a temperature compensated RC circuit was composed both to obtain half duty cycle and have a constant charge and discharge time with temperature change. A current source with two types of gate-oxide transistor combinations was able to obtain the reference voltage and had an ultra-low temperature coefficient, thus mitigating frequency variation with regard to temperature. The proposed voltage-controlled oscillator was implemented in a low power 65-nm CMOS process and occupied 0.011 mm2. Measurements showed that the voltage-controlled oscillator operated at 4.75-5.09 MHz with a supply voltage of 1.0 V, and its DC power consumption was 40 μW including a 3-stage buffer. A low frequency variation of 41.8 ppm/°C was achieved for the temperature range of 20 to 100 °C.