3
Trigger Mode Distributed Wave Oscillator
Many of today’s electronic systems use an oscillator circuit as a high frequency
signal source. In the last decade or two, many transmission line-based new
traveling or standing wave oscillator techniques have been introduced as a
very high frequency signal source with the availability of oscillation phases at
the tap points along the line. Availability of such GHz-range, high-resolution
oscillation phases is one of the most significant advantages of these oscil-
lators compared to their LC-based lumped counterparts. LC-based lumped
ones use two reactive components, an inductor and a capacitor, to create a
resonant circuit, in an ideal case indefinitely transferring the energy from one
to the other. However, in reality, the loss mechanisms associated with these
reactive devices (can be modeled as resistance (R) or transconductance (G)
elements) require active amplifying circuitry to compensate for these losses.
The well-known classical implementation for such an active compensation
circuit is a negative resistance circuit formed by cross-coupled active devices.
The metal oxide semiconductor field effect transistor (MOSFET) implemen-
tation of this configuration is shown in Figure 3.1. The resultant oscillation
frequency depends on the inductance and the capacitance values and can be
written as
f
osc
=
1
2π
L
tank
C
tank
(3.1)
Similarly, distributed counterparts can be constructed using transmission
lines. A transmission line is, in general, parallel running conductors sepa-
rated by a dielectric material. Microstrip line (Figure 3.2), coplanar waveguide
(Figure 3.3), coplanar strip line (Figure 3.4), and differential coplanar wave-
guide (Figure 3.5) are some of the most common transmission line structures.
Although any of these structures can be used to construct an oscillator, the
differentially symmetric ones are more favorable since the opposite phases
of a signal are already available (coplanar strip line and differential coplanar
waveguide).
Since these transmission lines effectively represent a distributed LC struc-
ture, an oscillator similar to a lumped LC tank oscillator can be formed as
shown in Figure 3.6. In this figure, L
0
, C
0
, R
0
, and G
0
represent inductance
per unit length, capacitance per unit length, resistance per unit length, and
conductance per unit length for a differential transmission line stretching in
the z-direction. The inductance per unit length and capacitance per unit length
determine the phase velocity of the wave propagating. The phase velocity of
23
24 High Frequency Communication and Sensing: Traveling-Wave Techniques
L
tank
R
loss
C
tank
G
loss
L
tank
R
loss
C
tank
G
loss
I
OSC
V
DD
FIGURE 3.1
Lumped LC tank oscillator.
a wave is as follows:
v =
1
L
0
C
0
(3.2)
where L
0
and C
0
are inductance per unit length and capacitance per unit
length, respectively. Then, for a given total length of transmission line, the
Cross-section
Top view
Ground
Dielectric
Signal
FIGURE 3.2
Microstrip line.
Trigger Mode Distributed Wave Oscillator 25
Cross-section
Top view
Signal
Ground
FIGURE 3.3
Coplanar waveguide.
Cross-section
Top view
Signal+
Signal–
FIGURE 3.4
Coplanar strip line.
Cross-section Top view
Signal+
Ground
Signal–
FIGURE 3.5
Differential coplanar waveguide.
½L
0
dx
½R
0
dx
½L
0
dx
½R
0
dx
C
0
dx
G
0
dx
x
FIGURE 3.6
Distributed oscillator structure using transmission lines.
26 High Frequency Communication and Sensing: Traveling-Wave Techniques
oscillation frequency can be calculated as
f
osc
=
1
L
tot
C
tot
(3.3)
where L
tot
and C
tot
are the total inductance and total capacitance along the
transmission line. Again, cross-coupled active amplifiers are used to compen-
sate for the conductor and substrate losses. Thanks to the distributed nature
of these transmission line oscillators, multiple phases of an oscillation are
available along the transmission line, whereas only two 180
opposite phases
are available in the case of lumped LC tank oscillators. Distributed wave os-
cillators, rotary traveling wave oscillators, and standing wave oscillators are
different classes of existing transmission line-based oscillators all utilizing the
distributed LC nature of a transmission line structure. These existing topolo-
gies will be touched upon briefly in Sections 3.1 to 3.3. Section 3.4 introduces
a new topology, trigger mode distributed wave oscillator (TMDWO) [7], and
discusses its advantages and disadvantages compared to existing topologies.
Section 3.6 presents a test structure and the related measurement results of
the proposed technique, and Section 3.7 is the conclusion.
3.1 Commonly Used Wave Oscillator Topologies
One of the earliest traveling wave oscillator inventions was distributed wave
oscillator [2–4,9,10,16]. Figure 3.7 shows a simplified distributed oscillator
structure. The actual shape can be in any closing geometric form bringing
point Ato the vicinity of point B so that a dashed AC coupled connection can
V
DD
V
BIAS
R
match
C
byp
Transmission
lines with
characteristic
impedance Z
0
R
match
A
B
FIGURE 3.7
Basic distributed oscillator structure.

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