A noise rejective VCO with build-in active LC filter

VCO is the key component in PLLs, and is easy to be interfered by the noise on control voltage or power supply. In this article, a build-in LC filter is inserted into a single-end VCO which is named BF-VCO. The LC filter consists of a regulated cascode active inductor and a capacitor. And the low-pass bandwidth is not greater than 1.6MHz. The measurement spectrum shows that the noise received by the succeeding ring oscillator is attenuated for about 20dB, while the white noise floor changes little.