High Order Harmonic Oscillators in Microwave and Millimeter-wave ...

2 Oscillators
• AM and FM noise (specified in dBc/Hz below carrier, offset from carrier)
• frequency stability (specified in PPM/ ◦ C)
2.2 Feedback Oscillator
In the most general sense, an oscillator is a nonlinear circuit that converts DC power
to an AC wave form. In this study, a feedback oscillator described in chapter 5 and a
negative resistance oscillator described in chapter 3, 4, 6 are adopted. In this section, the
feedback oscillator which is used from low frequency to microwave band is explained. Most
microwave and millimeter-wave oscillators provide sinusoidal outputs, which minimizes
undesired harmonics and noise sidebands. The basic conceptual operation of sinusoidal
oscillator can be described with the linear feedback circuit shown in Fig. 2.1. An amplifier
with voltage gain in ‘A’ has an output voltage V 0 . This voltage passes through a feedback
network with a frequency dependent transfer function H(ω), and is added to the input V i
of the circuit. Thus the output voltage can be expressed as
V 0 (ω) = AV i (ω) + H(ω)AV 0 (ω), (2.1)
which can be solved to yield the output voltage in terms of the input voltage as
V 0 (ω) =
A
1 − AH(ω) V i(ω). (2.2)
Vi(ω)
A
V0(ω)
H(ω)
Fig. 2.1: Block diagram of a sinusoidal oscillator using an amplifier with a frequency
dependent feedback path.
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