The performance of voltage controlled oscillator (VCO) is of great importance for any telecommunication or data transmission network. Here, voltage controlled oscillators (VCOs) using three-transistor NAND gates have been designed. New delay cell with three-transistor NAND gate has been used for designing the ring based VCO circuits. Three-, five-, and seven-stage VCOs have been proposed. Output frequency has been controlled with supply voltage variation from 1.8？V to 2.4？V. Three stage VCO shows output frequency variation in the range of 3.2909？GHz to 4.2280？GHz whereas power consumption varies in the range of 335.4071？μW to 486.1816？μW. Five-stage VCO depicts frequency in the range of 1.9406？GHz to 2.5769？GHz with power consumption variation from 559.0118？μW to 810.3027？μW. Moreover a seven-stage VCO shows frequency variation from 1.3984？GHz to 1.8077？GHz. Power consumption of seven-stage VCO varies from 782.6165？μW to 1134.400？μW. Phase noise results for these VCOs have also been obtained. Power consumption, output frequency, and phase noise results of proposed circuits have been compared with earlier reported circuits, and the proposed circuits show significant improvements. 1. Introduction Oscillators are the？ most fundamental blocks in various communication systems. With each generation of communication and microprocessor technology data rates are increasing at a very fast pace. In modern high performance systems phase-locked loops (PLLs) are the commonly used circuit component with wide application in frequency synthesis, clock, and data recovery [1–3]. PLL block contains a phase detector, a charge pump, a loop filter, and voltage controlled oscillator circuit. VCO is the major part of PLL circuit and it affects the system performance in terms of power consumption and noise performance. In modern VCO designs power consumption and high output frequency range have become important performance metrics. Two widely used VCO types are LC tank and CMOS ring based circuits. Combination of capacitor and inductor on integrated circuits consumes large layout area in LC tank based VCO designs [4–6]. CMOS ring based oscillators show advantages due to ease of controlling the output frequency and nonrequirement for on chip inductors [7, 8]. With the beginning of very large scale integration (VLSI) technology CMOS based VCOs are more accepted in PLL systems. These are also easier to integrate and provide wide tuning range. Further, with the rising demand of portable devices like cellular phones, notebooks, and personal communication devices, the need for power
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