The usage of high-voltage VCG for increasing the accuracy of phase auto-adjustment systems of frequency

Abstract

Problems of phase-locked-frequency (PLL) systems are considered in the work, which are one of the main
components of modern communication equipment. From the analysis of recent research and publications by the authors, it was found
that the highest quality voltage-controlled generators (VCG) are still mostly implemented on discrete circuits that can require a
supply voltage of up to 30 V, so the developers of modern PLL systems or radio frequency systems face the task of connecting lowvoltage microcircuits PLL and high-voltage VCG. This work examines the structure of a typical loop of high-frequency mixed PLL
systems, which contain both fully digital units, such as feedback dividers and phase detectors, as well as precision analog circuits -
charge pump nodes and VCG. The characteristics of the main blocks of mixed PLLs, and methods of their improvement are outlined.
An example of an available high-integration scheme is shown. The main features of the PLL system, which affect the quality of its
operation, are highlighted - capture time, phase noise and parasitic frequencies, and approaches for including circuit elements to
improve these characteristics are recommended. Examples of recommended active filter configurations with pre-filtering, inverting
and non-inverting amplifier connections are given. The advantages and disadvantages of inverting and non-inverting scheme
topology are determined. In the work, attention is paid to the selection of the operational amplifier for the maximum use of the
capabilities of the active filter in the structure of the PLL. It was determined that, in addition to the bandwidth, it is important to take
into account such basic parameters as voltage noise density, current noise, input current and the range of input common-mode
voltage. As a result of the analysis, it was found that to achieve the best performance of the PLL, an operational amplifier with a low
voltage noise density to reduce phase noise, a small input current to reduce error and a defined range of input voltages to be able to
operate with a unipolar supply is required. An example and characteristics of a fully integrated high-quality PLL system is given,
where the wideband VCG is integrated directly into the microcircuit crystal.