RF Electronics Chapter 6: Oscillators Page 196
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 6.40. Layout for 1GHz Microstrip resonator.
The length of TL3 is made small as is practicable to minimise the loading of the resonator
due to the rest of the circuit. The length of TL3 should be several times larger than the
width of the connecting tracks, to ensure a uniform current distribution on the input and
output connectors. The 50 Ω track width of TL1 is 1.84 mm. As a result, the smallest
length of TL3 is about 3 mm. Resistors R1 and R2 are placed at the input and output, to
firstly provide a reasonable termination impedance to the amplifier at frequencies other
than the resonant frequency and secondly to provide some fine tuning for the resonator
loading, and thus the loop-gain of the oscillator. Figure 6.40 shows the layout for the
resonator and the coupling capacitors. The left end of the circuit is grounded.
Figure 6.41 shows the amplitude and phase of the resonator of figure 6.40, as a function
of frequency.
Tuning Step 1: Tune the length of the resonator Lr1, to ensure that the resonator has a
maximum gain from port 1 to port 2 at the desired oscillating frequency in figure 6.41.
The gain at other frequencies should be low, to ensure that the oscillator does not oscillate
at another frequency.
The resonator has a well-behaved response at 1 GHz, but if the amplifier gain is too high,
there is a possibility of oscillation at the secondary response of 1.34 GHz. The loop gain
of the amplifier and resonator must thus be carefully controlled to ensure that only
oscillation at 1 GHz is possible.
Figure 6.41. Resonator transfer function, amplitude and phase.
RF Electronics: Design and Simulation
196 www.cadence.com/go/awr
