RF Electronics Chapter 6: Oscillators Page 178
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
emitter voltage of 4.5 Volt, a base voltage of 5.3 Volt is desired, so that a biasing resistor,
of about 5.3V/1.5 mA = 3.53 k is required for R2. The nearest E12 value is R2=3.3 k.
A 2.7 k resistor is then required for R3 to then obtain close to 4.5 V at the emitter of the
transistor. The annotation setting allows the circuit voltages to be indicated on the circuit
diagram in Microwave Office, and allow the biasing and voltages to be checked.
Figure 6.7 shows the performance of the amplifier from 50 MHz to 150 MHz. The gain
of 5.24 dB is the magnitude of S(2,1), assuming 50 source and load impedances. The
input impedance is 982 and the output impedance is 19 , with a significant reactive
component that will affect the resonance of the Colpitts oscillator if it is not allowed for
in the design process.
Figure 6.7. Amplifier Performance.
Step 3: Design a Resonator
Figure 6.8. Colpitts resonator network.
The resonator must be a frequency selective network, to ensure that the conditions for
oscillation only apply at one frequency. In addition, the network must be matched to the
input impedance and output impedance of the amplifier and have a high Q. Figure 6.7
shows the amplifier real input impedance is 982 Ω. That is the impedance used for Port 2
RF Electronics: Design and Simulation
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