It consists of an odd number of inverters, or NOT ports, in series, with the output signal of the last inverter being fed back to the input of the first inverter. The circuit functioning principle is similar to relaxation oscillators, although the technical literature often treats them as different things. The ring oscillator is one of the most simple, effective, and reliable oscillatory topologies, and it is widely implemented in the industry. The most popular relaxation oscillator is the astable multivibrator, shown in Figure 2. Because it is possible to use different time constants and thresholds for the charging and discharging states, relaxation oscillators can generate asymmetrical waveforms with different shapes. The amplitude and frequency of relaxation oscillators are defined by the time constants of the charging/discharging networks and the threshold levels of the switching devices. When the threshold is reached, the reactive device is discharged down to the lower-level threshold, after which the circuit switches back to the initial state, and the process repeats. The principle consists of using switching devices, such as comparators, op-amps, and transistors, to charge a reactive device (capacitor or inductor) until the voltage level reaches an upper-level threshold. Relaxation oscillators, on the other hand, use non-linear devices to create an unstable network. These circuits are designed to follow the Barkhausen oscillation criterion, which states that the loop gain must be equal to 1 and the phase shift around the loop equal to 2π to sustain oscillatory regime at the desired frequency.įigure 1: Resonant Oscillator using a crystal Crystal-based oscillators, which also fall into the category of resonant circuits, replace the LC circuit with a crystal with a stable resonant frequency. Resonance oscillators use an LC tank in the feedback path of a linear circuit to provide positive feedback at a specific frequency (Figure 1). There are two main types of oscillatory circuits: resonant linear oscillators and relaxation oscillators. To achieve this goal, the circuit consists of a positive and unstable feedback network. In general, the main objective of an oscillator is to generate a voltage or current signal at a specific frequency. There are many types of oscillators described in the literature, such as resonance oscillators and crystal-based oscillators. Therefore, it is impossible to design digital processing circuits without oscillators. The clock signal allows the circuit to perform sequential operations and gives it the ability to precisely set the time of important events. In digital systems, oscillators are responsible for producing the heart of sequential circuits: the clock. From audio synthesizers to lock-in amplifiers, they play a fundamental role in signal generation, waveform synthesizing, and timers. Oscillators are among the most important and versatile structures in electronics. We will talk about the basic concepts of ring oscillators, the functional description of the ring oscillator, the different topologies that can be applied, and the many applications of the circuit. Ring oscillators provide a wide tuning range, a small footprint, and multiple phase outputs. In this article we will discuss the ring oscillator, which is one of the most popular circuit topologies in the digital world.
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