A PLL with high-speed operating discrete loop filter

In this paper, the proposed small size PLL works stable with the discrete loop filter which is controlled by voltage controlled oscillator’s output signal. A switch controlled loop filter is introduced into the proposed PLL instead of a conventional 2 nd -order loop filter. Those three switches are controlled by the very high frequency output signal of voltage controlled oscillator. The switches are also controlled by UP/DN signals and ‘on/off’ depending the presence of UP/DN signals. A negative feedback functioned capacitor with a switch does make it possible to integrate the PLL into a single chip. The proposed PLL works stably even though a total of small 180pF capacitor used in the discrete loop filter. The proposed PLL has been designed with a 1.8V supply voltage, 0.18um multi - metal and multi - poly layer CMOS process and proved by Hspice simulation.