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Abstract

A voltage controlled oscillator circuit comprises a first lowpass OTA-C filter with differential input and differential output and a second lowpass OTA-C filter with differential input and differential output. A non-inverted output terminal of the first OTA-C filter is connected with a non-inverted input terminal of the second OTA-C filter, an inverted output terminal of the first OTA-C filter is connected with an inverted input terminal of the second OTA-C filter, a non-inverted output terminal of the second OTA-C filter is connected with an inverted input terminal of the first OTA-C filter, and an inverted output terminal of the second OTA-C filter is connected with a non-inverted input terminal of the first OTA-C filter. Gate widths of input terminals of OTAs in each OTA-C filter are set appropriately, and initial values of terminals are set by nMOSFETs 3-6, and oscillation output is outputted from the non-inverted output terminal and the inverted output terminal of the second OTA-C filter. According to the voltage controlled oscillator circuit, oscillation of a waveform of a sine wave can be obtained, switching noise can be reduced, and common mode noise can be removed by differential operation. Further, susceptibility to outside noise from power sources, circuit boards, etc. can be reduced, since sensitivity is reduced by utilizing OTA-C filters derived from doubly resistively terminated LC filters. And consequently, oscillation output including little phase noise is obtained.

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