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RF Electronics Chapter 6: Oscillators Page 174 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Oscillator Design Process 1: Design the Feedback network to have the correct frequency selective behaviour at the required operating frequency. A high Q network will have a rapid change of phase with frequency resulting in a lower phase noise of the resulting oscillator. 2: Select or design the amplifier to have the required gain at the operating frequency. The input and output impedances should match the expected loads to be seen by the frequency selective network. 3: Simulate the amplifier and ensure the biasing is correct to provide the required gain and phase shift at the operating frequency. 4: Connect the frequency selective network and amplifier as shown in figure 6.2, and do a linear analysis to ensure that the required gain (>1) and phase (V2 in-phase with V1) conditions are satisfied. In MWO the OSCTEST element is specially designed to perform this function and is used in place of the switch shown in the above diagram. It is important that the secondary parameter FC of OSCTEST be set to be above the expected fundamental frequency and below the second harmonic frequency. Figure 6.2. The use of OSCTEST for linear analysis of oscillators. 5: Once the circuit has been adjusted to have the correct gain and phase for oscillation, modify the linear circuit by replacing the OSCTEST probe with the OSCAPROBE. The OSCAPROBE is connected to ground at the point where the switch was, as shown in figure 6.3. Amplifier Frequency Selective Network Oscaprobe Figure 6.3. The use of OSCPROBE for nonlinear analysis of oscillators. The OSCAPROBE is a network that is a short circuit at the specified frequency of oscillation and an open circuit at all other frequencies, the voltage amplitude and phase is adjusted, until no current flows through the probe, under which conditions the correct RF Electronics: Design and Simulation 174 www.cadence.com/go/awr

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