Analytical model for CMOS cross‐coupled LC‐tank oscillator

Abstract

Periodic steady-state behaviour of cross-coupled LC-tank oscillator is of critical importance in ultra-low power, lowvoltage transceiver circuits. Understanding the major factors affecting amplitude, oscillation frequency and power consumption would lead to more optimised oscillator design particularly for short-range wireless transceivers. This study presents a new approach for evaluating the amplitude of the main component, oscillation frequency and power consumption of cross-coupled LC-tank oscillator. Three major factors, affecting oscillator functionality are examined. In order to obtain a general design methodology, the effects of oscillator parameters such as transistors' sizes, inductor and capacitor values are investigated. An intuitive discussion about oscillator behaviour and a design procedure are presented. The theoretical results are verified by circuit simulations in the 0.18 µm CMOS process.

Electronic Circuit with Controllable Negative Differential Resistance and its Applications

“…A distinctive feature of the first-class oscillators is the presence of a negative real part in the input impedance. Examples of such oscillators are numerous Colpitts, Clapp, Hartley oscillator circuits, and their modifications [27][28][29][30], as well as cross-coupled CMOS oscillators [31][32][33][34]. The second class of microwave oscillators supposes to use a tunnel diode or a Gunn diode [35,36], which have an NDR region in the N-type current-voltage characteristics.…”

A high‐power and high‐efficiency CMOSVCO

“…In the VCO circuit, instead of using commercial design kit varactor with higher loss, we have used custom designed diode‐connected NMOS transistors (TN3 and TN4) as the variable capacitor for tuning the frequency. This arrangement because of its lesser loss and the operation of the VCO in the verge of voltage‐limited regime provides larger DC voltage at the drain of core transistors and consequently help in extracting high‐RF output power with high efficiency. Furthermore, the diode‐connected tail transistor (TN_tail) which reduces the power dissipation of the core circuit by reducing the current through the core transistors (because it increases the node voltage V s at S) is also responsible in achieving high efficiency of the VCO.…”

“…To get an idea that how the design parameters impact the performance of the output power and efficiency, we have used Fourier analysis technique to obtain the output power. Figure shows the simulated output voltage waveform at the node D1 (G2) and D2 (G1) and simulated current waveform of the transistors TN1 and TN2.…”

“…As the transistor nonlinearity has a considerable effect on frequency of oscillation of the VCO, to find out the oscillation frequency, it is needed to consider the transistor's nonlinear effects. The frequency of oscillation of the cross‐coupled LC tank VCO, considering the nonlinear effects of the transistor, is given by where C = C eq + C var and C eq is equivalent capacitance at the drain node of the transistor TN1 (or TN2) except the capacitance C var , and C var is the variable gate capacitance of NMOS diode, TN3 (or TN4). Equation shows that the V dc plays an important role to determine the oscillation frequency.…”

Analysis and design optimization of enhanced swing CMOS LC oscillators based on a phasor based approach

“…In [9] and [16], the amplitudes for current biased Colpitts oscillators and voltage biased cross-coupled oscillators were obtained respectively with the square law MOSFET characteristics requiring no polynomial fitting. In our work, the amplitude is evaluated with the square law MOSFET level-I model.…”