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Home Transistor Oscillators NegativeResistance Oscillators General Types  
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General TypesAuthor: Leonard Krugman Negativeresistance oscillators may be divided into two general classes: voltage controlled; and current controlled. The voltagecontrolled oscillator is characterized by a high resistance load, and a low resistance power supply (constant voltage). The fundamental schematic of a typical oscillator of this type is illustrated in Fig. 67 (A). Fig. 67. (A) Voltage controlled negative resistance equivalent circuit. (B) Idealized currentvoltage characteristic. This oscillator is composed of three major parts: the resonant LC circuit, the negative resistance of the oscillator, and the dc supply voltage E_{bb}.
Fig. 68. (A) Currentcontrolled negative resistance equivalent circuit, (B) Idealized currentvoltage characteristic. The currentcontrolled type is shown in Fig. 68 (A). This oscillator is characterized by a low ac load and a high dc power source (constant current). Figure 68 (B) represents the idealized currentvoltage characteristics for this negativeresistance oscillator. As in the voltagecontrolled type, the negativeresistance region is limited to a section of the operating range, and the bias is established somewhere in the middle of this negativeresistance region using a constant current source. The last condition to be satisfied for sustained oscillation is that the ac load of the resonant circuit must be less than the absolute value of negative resistance of the oscillator at the operating point. The series LC circuit, the resonant impedance of which is close to zero, is the ideal load for this application.


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