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A wide variable-range CMOS–VCXO for IC

✍ Scribed by Yuji Lee; Madoka Komatsubara; Hideo Otsuka; Yoshifumi Sekine

Publisher
John Wiley and Sons
Year
2000
Tongue
English
Weight
218 KB
Volume
130
Category
Article
ISSN
0424-7760

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✦ Synopsis

Recently, miniaturization, low power consumption, and high-frequency stability have been required in crystal oscillators as a frequency source, because of the rapid development of mobile communications, typified by cellular phones. Usually, a VCXO (Voltage Controlled Crystal Oscillator) has been included in PLL. And it has been required that the VCXO should be implemented on a CMOSIC chip. The oscillating frequency of a traditional VCXO has been controlled by capacitance variation of a varactor diode. But it is difficult to implement the varactor diode on an IC chip.

In our previous study, we showed that a transistor VCXO utilizing the MOSFETs Miller capacitance of a variable capacitance circuit had a wide frequency variable range. On the other hand, in a CMOSVCXO, the Miller capacitance has decreased. Therefore, a wide frequency variable range could not be obtained by utilizing the Miller capacitance in the CMOSVCXO.

In this paper, first, a variable capacitance circuit is realized in order to construct a wide-variable-range CMOSVCXO for IC. The variable capacitance circuit is composed of a MOSFET as a voltage controlled resistance. Next, the CMOSVCXO is constructed by the variable capacitance circuit and a CMOS crystal oscillator. As a result, we show that the CMOSVCXO has a wide frequency variable range of about 400 ppm.

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