Electronic Devices and Amplifier Circuits

Hartley Oscillatorpower supply voltage V CC supplied to the transistor is through a path parallel to the tank circuit. Ineither of the oscillator circuits of Figure 10.5, power through V CC is supplied to the transistor andthe tank circuit begins to oscillate. The transistor is operating as Class C amplifier, that is, the transistorconducts for a short period of time and returns sufficient energy to the tank circuit to ensurea constant amplitude output signal. As we’ve learned in Chapter 3, Class C operation provides thehighest efficiency among all amplifier operations.10.6 Hartley OscillatorFigure 10.6 shows a simplified version of the Hartley oscillator.L 1L 2MCV CCFigure 10.6. Simplified circuit for the Hartley oscillatorIn a Hartley oscillator the feedback is provided through a coil pair as shown in Figure 10.4(b). Forthe oscillator circuit of Figure 10.6 the frequency of oscillation isω 0 =1----------------------------------------------------------------------------------------------------------CL ( 1 + L 2 + 2M) – ( L 1 L 2 – M 2)( h ob ⁄ h ib )(10.14)where M is the mutual inductance * and h oband h ibare the h−parameters representing the outputadmittance with open−circuit input and input impedance with short circuit output respectively, asdiscussed in Chapter 3.10.7 Colpitts OscillatorFigure 10.7 shows a simplified version of the Colpitts oscillator. In a Colpitts oscillator the feedback isprovided through a capacitor pair as shown in Figure 10.4(c).* For a detailed discussion on mutual inductance, please refer to Circuit Analysis II with MATLAB Computing andSimulionk/SimPowerSystems Modeling, ISBN 978−1−934404−19−5.Electronic Devices and Amplifier Circuits with MATLAB® / Simulink® / SimElectronics® Examples, Third EditionCopyright © Orchard Publications10−7