A wide variable range VCXO for IC

We suggest the use of a Miller capacitor as the variable capacitance circuit of the BJT-VCXO (VCXO using a bipolar junction transistor). When the external MOSFET's gate-drain capacitance is 10 pF, we show that the BJT-VCXO using this variable capacitance circuit has a wide frequency variation of about 500 ppm. Also, we suggest the use of the MOSFET's resistance change as the variable capacitance circuit of the CMOS-VCXO (VCXO using a CMOS crystal oscillator). When the external gate-drain capacitance is 30 pF, we show that the CMOS-VCXO using this variable capacitance circuit has a wide frequency variation of over 330 ppm.