RF Electronics Chapter 10: Operational Amplifiers Page 359
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
output voltage to that obtained from the LMH6629, so that a fair comparison to be made.
Figure 10.23 shows the phase noise for the ideal OpAmp oscillators of figure 10.21, and
the Spice simulations of the LMH6629 OpAmp oscillators, using the circuit values shown
in figure 10.21.
Figure 10.23. Phase noise for 10 MHz Hartley and Colpitts oscillators using OpAmps.
For ideal OpAmps, the Hartley oscillator with an ideal resonator (Q = 10000) has a phase
noise of -153.8 dB. The same oscillator with a Q = 200 has a phase noise of -136.5 dB,
and the corresponding Colpitts oscillator has a phase noise of -136.3 dB. For the
LMH6629 OpAmp circuits with a Q = 200, the phase noise of the Hartley oscillator is
-130.3 dB and the Colpitts oscillator is -132.6 dB. There is thus little difference between
the phase noise of a Hartley and Colpitts oscillator.
For the ideal OpAmps, there is a 153.8 - 136.5 = 17.2 dB difference between the phase
noise for the ideal resonator and the resonator with a Q = 200. For the LMH6629 oscillator
the corresponding difference is 137.9 – 130.3 = 7.6 dB. The phase noise is thus dominated
by the resonator Q.
Figure 10.24. Spectra for 10 MHz Hartley and Colpitts oscillators using OpAmps.
RF Electronics: Design and Simulation
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