| Summary: | 博士 === 長庚大學 === 電子工程學系 === 98 === In this thesis, a novel trans-directional (TRD) coupler has been designed. Applications of quadrature voltage controlled oscillator (QVCO) and balun are presented and good performances are achieved. Compared with the traditional coupled-line and branch-line couplers, the TRD coupler uses a different kind of coupling mechanism. Various new applications should be worth to be investigated.
At first, the required condition for TRD operation is derived. Then it shows how to realize the TRD coupling by periodically loading couple lines with shunt susceptances. Two kinds of the original and size-reduced prototypes are fabricated by single layer PCB technology at 3.6GHz. Good agreement with simulated results is reached.
Next, a QVCO is realized by using the TRD couplers. The TRD couplers allow decoupling the DC path between input and output. Thus, they can eliminate off-chip biasing circuits. Since the quadrature signals are generated only by TRD couplers, the oscillator core can be optimized for circuit performance without considering the generation of quadrature signals. A Ka band QVCO fabricated in CMOS 0.18 um technology is designed. The measurement results of QVCO have -1.52 dBm output powers with less than 1 dB amplitude imbalance and less than 6° phase difference in the frequency range of 31.9 to 32.7 GHz. The best measured phase noise of the QVCO is -110.6 dBc/Hz at 1 MHz offset from the center frequency.
Finally, a new type planar balun is proposed by using the TRD couplers. The syntheses and performances of the balun are derived and analyzed. No via-holes to ground are needed in the proposed balun which can decrease the phase errors caused by the inductive effects of via-holes. A new type of balun whose coupling is totally contributed by the capacitors is also discussed. It can make the composed lines of the balun routed in a small area to shrink the circuit size. Two prototypes are designed by single layer PCB technology. The first one is formed by -3 dB TRD couplers to achieve the best input matching results. The bandwidth is 1.93~2.67 GHz (32%). The second prototype is formed by -4.8 dB TRD couplers to shrink the dimension of the circuit to 16.8 mm × 39.4 mm. The bandwidth is within 380~460 MHz with the input return loss less than -11 dB, phase difference less than 1°, and amplitude imbalance is less than 0.16 dB.
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