A Wide Variable Range CMOS-VCXO for IC

Abstract

Recently, the crystal oscillator as a source of frequency standard have required miniaturization, low power consumption and high frequency stability because of the rapid development of the mobile communications represented by the cellular phones. It is necessary for PLL and so on to be composed of a VCXO (Voltage Controlled Crystal Oscillator). The VCXO should be implemented on CMOS-IC. Traditional VCXO is controlled by capacitance variation of a varactor diode. But it is difficult to realize the varactor diode on IC chip.
In our previous study, we showed that the transistor VCXO using the MOSFET's Miller capacitance had a wide frequency variation. But the Miller capacitance decreased with large amplitude. So, a wide frequency variation could not be realized the CMOS-VCXO using the Miller capacitance.
In this paper, first the variable capacitance circuit is realized in order to construct by the wide variable range CMOS-VCXO for IC. The wide variable capacitance circuit is composed of the MOSFET as the voltage controlled resistance. Next, the CMOS-VCXO is constructed by the variable capacitance circuit and the CMOS crystal oscillator. As a result, we will show that the CMOS-VCXO has wide frequency variation of about 400[ppm].