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Operational Amplifiers
Published in Michael Olorunfunmi Kolawole, Electronics, 2020
A relaxation oscillator is a circuit that repeatedly alternates between two states. The length of its stay at each state depends on the charging of a capacitor. Figure 4.21a shows the circuit of a square wave generator, also called a relaxation oscillator. This square wave generator is like the Schmitt trigger circuit in that the reference voltage (Vref) for the comparator action depends on the output voltage. For this oscillator, like the comparator amplifier, the reference voltage Vref is determined at node xx of Figure 4.21a using voltage divider rule: Vref=±Vcc(R2R1+R2)
Silicon Carbide Oscillators for Extreme Environments
Published in Sumeet Walia, Krzysztof Iniewski, Low Power Semiconductor Devices and Processes for Emerging Applications in Communications, Computing, and Sensing, 2018
Daniel R. Brennan, Hua-Khee Chan, Nicholas G. Wright, Alton B. Horsfall
The nonlinear oscillator (sometimes referred to as a relaxation oscillator) produces a waveform that is nonsinusoidal, such as a square wave, sawtooth or triangular waveform. The circuit topology comprises an energy storage component in conjunction with a nonlinear switching circuit. The energy storage component is often a capacitor; however, circuits based on the use of inductors have been demonstrated. Alternative implementations of this circuit comprise those that include a negative resistance device that periodically charges and discharges the energy in the storage element, resulting in abrupt changes in the output voltage of the circuit. Square wave relaxation oscillators are used extensively in digital electronics to provide the clock signal for sequential logic circuits such as timers and counters, whereas sawtooth oscillators are used specifically in time base circuits. An example of a single active device relaxation oscillator can be constructed using a uni-junction transistor (UJT) device. A UJT comprises one p-n junction, making it similar in structure to a p-n diode; however, it differs in the fact that it has three terminals and so it is also referred to as a double base diode. It is worth noting that while the UJT has a similar construction to a junction field-effect transistor (JFET), the operation in a circuit is significantly different. In a UJT, the current through the device is modulated by the bipolar current injected through the gate under forward bias, rather than by the influence of the depletion region formed in the channel [11] with the gate under reverse bias.
Basic Responses of First-Order Circuits
Published in Nassir H. Sabah, Circuit Analysis with PSpice, 2017
A nonlinear “threshold” device D is connected across the capacitor in Figure 11.39. The device changes its resistance R abruptly once the increasing voltage vC reaches a certain level or threshold. It is assumed that R is infinite for 0 < vC < 3 V, while the capacitor is charging. When vC=3V,R becomes zero, instantly discharging the capacitor, and immediately becomes infinite again when the capacitor is discharged. The capacitor starts charging again, and the cycle is repeated. vC is therefore a periodic waveform that repeats at a certain frequency, as illustrated by the solid-line in Figure 11.40. It is required to determine the frequency of oscillation. This type of oscillator, based on a nonlinear element, such as D, that repetitively charges and discharges an energy storage element is referred to as a relaxation oscillator.
On the Effect of Operational Amplifier Gain-bandwidth Product on the Performance of Basic Building Blocks
Published in IETE Journal of Education, 2022
Another interesting band-pass filter using an amplifier pole is shown in Figure 3(g) [29]. This uses positive feedback for the differentiator circuit of Figure 3(e). The transfer function of this circuit can be derived as where . The realized pole-Q of the band-pass filter is given as which can be controlled using β. Under the condition , an exact sinusoidal oscillator with oscillation frequency can be realized. If , then the circuit becomes a relaxation oscillator and generates a square wave or a triangular waveform when the input Vi is grounded, as shown in Figure 3(g). This circuit is given in several opamp application notes as a square wave generator [30].
Stabilization and synchronization of 5-D memristor oscillator using sliding mode control
Published in Journal of the Chinese Institute of Engineers, 2018
Muhammad Rafiq Mufti, Humaira Afzal, Fazal-ur- Rehman, Nisar Ahmed
During the past few years, there has been a great interest in the modeling and control of chaotic systems, which are basically nonlinear systems whose trajectories are highly dependent on initial conditions, and so any perturbation in the initial conditions may lead to unknown periodic oscillations in the neighborhood orbits. A memristor oscillator is one example of a chaotic system, which is prepared by replacing one or more elements of a conventional oscillator such as a Wein oscillator (Talukdar, Radwan, and Salama 2011), a Relaxation oscillator (Mosad et al. 2013), an Operational amplifier based oscillator (Elsamman, Radwan, and Madian 2013), or Chua’s oscillator (Zhong 1994). It is a nanosized solid state technology developed in 2008 (Strukov et al. 2008). Due to nonlinear behavior, these oscillators may cause chaotic effects in the oscillators in which they are being employed.