RF Electronics Chapter 6: Oscillators Page 189
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
For a low noise Hartley oscillator, the circuit of figure 6.19 is used as a starting point.
�he resonator impedance is the same as that of the Colpitts resonator, �rh � 1� �.
Just like the Colpitts oscillator, the resonator loading is minimised by adding a series
resistor Rsh and a buffer amplifier is added. Similar to the Colpitts oscillator, the
circuit parameters are tuned to achieve the lowest phase noise. Figure 6.25 shows
the resulting oscillator schematic.
Figure 6.26 shows that the phase noise of 143 dB is 12.9 dB lower than that of figure
6.22. The phase noise for both the Hartley and the Colpitts oscillator are nearly the same.
Changing the Q to 20000, does not reduce the phase noise, indicating that the transistor
parameters are the dominant limitation on the phase noise.
Figure 6.26 Phase noise of Colpitts and Hartley low noise oscillators.
Figure 6.27 Spectra of Colpitts and Hartley low noise oscillators.
Figure 6.27 show the spectra of the output signals. The predominant distortion is due to
even harmonics. Figure 6.28 shows the output waveforms from the oscillators. The output
voltages are close to 8V peak to peak, which is 80% of the supply voltage.
RF Electronics: Design and Simulation
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