A low phase noise integrated SiGe 18..20 GHz fractional-N synthesizer

The communication market demands broadband transmission, high density television (HDTV) and interactivity, whereby HDTV will become the leading application. All applications require a high number of individual channels, leading to a large number of up-and down-converters. These high needs can be served best with highly integrated SiGe MMICs. It has been demonstrated that the best suited RF-element to be developed is the local oscillator (LO) synthesizer, which fits well to the SiGe technology. The most critical building blocks of the LO are the voltage controlled oscillator (VCO) which is challenging in its phase noise behavior and the fractional-N´ divider with its large influence on phase noise and spurs. This paper will describe the flexible design of a MMIC, which can be used also as a PLL circuit together with an external oscillator in a broad frequency range.