Caption: FIGURE 11: (a) Type I SHG tuning curve
Inspecting [f.sub.L] expressed in Equation (2), when [C.sub.1] of the primary LC tank incorporates tuning varactors, there is a two-dimensional tuning curve
(frequency versus vtune or versus [C.sub.1]) as traditional VCO designs in literature.
The current flow through varactors [C.sub.var2], [C.sub.var4] and [C.sub.var6] are used to establish the unidirectional phases (A, B, C) by utilizing the monotonic tuning curve
of accumulation-mode MOS varactor.
The plot depicts the tuning curve
and represents the "receptive field" of the nerve from which the data were obtained.
In general, today's systems demand the largest possible frequency range, the lowest possible phase noise, a linear tuning curve
and insensitivity to load conditions.
This can be accomplished by varying the sweep rate (or shape of the tuning curve
) in some random way, but it is much easier to implement a scheme in which the start time of the sweep is pseudo-randomly selected.
The boundaries of each frequency tuning curve
were defined as the stimuli (intensity and frequency) that yielded these evoked, excitatory responses [22, 26].
A high SWR or unstable load not only causes VCO frequency pulling, but will also sometimes produce rapidly accelerated regions of the tuning curve
(voltage-to-frequency transfer function).
As shown in Equation 4, [[omega].sub.0](V) is a nonlinear function of V, and therefore, in general, the tuning curve
will not be a perfectly straight line.
The VCO's typical tuning curve
over temperature is shown in Figure 2.
In addition, using a varactor with a less abrupt tuning curve
reduces the tuning diode's nonlinearity.
Since the upper part of the tuning curve
is much more nonlinear than the lower part, six switching points are used in the upper part (resistors R+) and only two switching points are used in the lower part (resistors R-).