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As has been shown in the previous section, the maximun value of the conversion gain which can be reached by means of controlling of the harmonic content of the HSOM is about [G.sub.c] [approximately equal to] w -20dB.
In order to improve the conversion gain of the HSOM, a pair of complex conjugate poles, with small negative real part, will be created around the center frequency of the input signal [f.sub.RF] = 11.5 GHz.
Since the magnitude of the amplification effect which is exploited in order to enlarge the magnitude of the input RF signal is greater for smaller values of [absolute value of [r.sub.p]], the conversion gain of the HSOM increases as the real part of the pole pair approaches zero.
In order to prove that the two factors that determine the conversion gain are controlled independently, three different HSOM circuits with different harmonic content have been designed.
Thus, it is shown that the conversion gain of the HSOM depends on two different factors, namely, the harmonic content of the autonomous signal and the working regime close to a Hopf bifurcation point, and that these two factors can be independently controlled.
In order to analyze the linearity of the HSOM working as a mixer, the two figures of merit which are commonly used to characterize conventional amplifiers [8-10,26,27], and mixers [13,15,17,28], namely, the 1 dB compression point and the third order interception point (IP3), will be calculated.
In the case of the HSOM, the 1 dB compression and the IP3 cannot be directly calculated as in a conventional mixer.
The power difference Ps is practically constant for all the pairs ([V.sub.o], [V.sup.3.sub.o]) and, in the worst considered case, with [P.sub.RF] = -40dBm, its value is about 60dB, which means that the HSOM circuit provides low third order distortion.
In order to analyze the influence of the proximity of the working regime of the HSOM to the Hopf bifurcation point on the linearity of the mixing operation, the 1 dB compression point and the third order distortion [P.sub.[delta]] will be calculated for different circuits, with the same harmonic content, operating at different distances from the Hopf bifurcation point.
Therefore, the conversion gain of each HSOM is given by the value of the negative real part of the created complex conjugate pair of poles.
The conversion gain of the HSOM circuits with different operating regimes, calculated at the center of the working band as [G.sub.c] (dB) = [P.sub.IF] (dBm) - [P.sub.RF] (dBm) has been represented in Fig.
9, the HSOM working close to a Hopf bifurcation point can be represented through the equivalent circuit represented in Fig.
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