China
Africa
Explore chapters and articles related to this topic
Electronic Circuits
Published in Dale R. Patrick, Stephen W. Fardo, Electricity and Electronics Fundamentals, 2020
Dale R. Patrick, Stephen W. Fardo
A distinguishing feature of the Hartley oscillator is its tapped coil. A number of circuit variations are possible. The coil may be placed in series with the collector. Collector current flows through the coil in normal operation. A variation of this type is called a series-fed Hartley oscillator. The circuit of Figure 4-72 is a shunt-fed Hartleyoscillator. IC does not flow through T1. The coil is connected in parallel or shunt with the dc voltage source. Only ac flows through the lower part of T1. Shunt-fed Hartley oscillators tend to produce more stable output.
Multistage and Feedback Amplifiers
Published in Nassir H. Sabah, Electronics, 2017
If part of the voltage developed across the RLC circuit of a tuned amplifier is fed back to the transistor input, sustained sinusoidal oscillations will result. In the Colpitts oscillator, C is replaced by two capacitors in series, the feedback voltage being the voltage across one of these capacitors. In the Hartley oscillator, L is replaced by two inductors in series, with or without coupling between them, the feedback voltage being the voltage across one of these inductors. Both types of oscillators are widely used in practice, particularly in broadcast receivers.
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
This chapter has demonstrated the possibility of fabricating high-temperature electronic oscillators using SiC technology. The low maturity of SiC in comparison to silicon precludes the use of microprocessor-controlled oscillators; however, analog circuits based on discrete components have been shown to offer performance that is suitable for a wide range of applications. Predictions as to the frequency of the oscillations require accurate knowledge of the parasitic capacitances in the circuit, but more crucially the variation with temperature of these parasitics and the discrete components used in the circuit. Utilizing device characteristics that were determined over the temperature range of interest, a high-temperature, Colpitts-based VCO was demonstrated. The circuit was used to show that it is possible to control the frequency drift at high temperature along with AM and FM of two high-temperature oscillators working at temperatures up to 300°C. The physical design of the Colpitts oscillator specifically lends itself to miniaturization, featuring a capacitive feedback path, offering greater frequency stability and physically smaller components than the inductive feedback path found in the Hartley oscillator. The Colpitts oscillator also demonstrates an inherently more powerful self-starting-up ability than the Clapp oscillator, resulting in the allowed utilization of lower components with larger tolerances, which is typical in the low technological maturity SiC devices. LC oscillators provide a simple solution for producing high-frequency sine waves; these circuits contain a tuned LC tank and an active device arranged in an amplifier layout; and they are particularity useful in situations where the energy supply can be intermittent due to their self-starting ability.
Voltage-controlled oscillators using CFOAs with correction terminal Z
Published in International Journal of Electronics, 2023
Table 2 summarises results of a comparative analysis between the proposed voltage-controlled oscillator circuits and previous works published in the literature. The comparative analysis begins with the classic Colpitts and Hartley three-point oscillator circuits (Sedra et al., 2020; Seifart, 2003; Tietze & Schenk, 2008), as they are the basic configurations for obtaining all fixed-frequency or frequency-changing circuits over a certain range. The basic advantages of these circuits are that they contain one or two BJT or MOSFET and, as a result, the operating frequency range of about 100kHz and reaches the GHz-range. Also, in the last ten years there have been a large number of three-point configurations implemented as monolithic integrated circuits. The disadvantages of Colpitts and Hartley oscillators are related to the small value of the equivalent quality factor, and hence the insufficient stability of oscillation frequency and amplitude. This is largely due to the additional passive and active components (resistor dividers or various current mirrors) that are used in the circuit structure necessary to ensure the operating point of the transistors. Also, typical values of the coefficient of nonlinear distortions reach up to 3%, and in some cases (at a larger amplitude of the output signal) is obtained with greater values. Compared to the three-point configurations, only one passive amplitude tuning element (grounded resistor RS) is used in the proposed oscillators, and as a result, the frequency stability factor SF can be obtained with a larger value. Also, the output sinusoidal signal for the proposed circuits is obtained after a buffer (Figure 3), which is the output stage of the CFOA, and as a result, the parameters of the load do not affect the parameters of the resonant LC circuit. Moreover, the nonlinear distortion is obtained with a smaller value and the coefficient of the amplitude stability is with a larger value. The proposed oscillator work with a higher voltage compared to the classic LC oscillator circuits, but the supply current is below 5mA in dynamic mode of operation. As a result, the maximum power consumption does not exceed 100mW at a bipolar supply voltage.