Yi-Chyun Chiang

Design of a wide-band lumped-element 3-dB quadrature coupler

Analysis and design techniques for designing a lumped-element 3-dB quadrature coupler with wide-band flat coupling are proposed for microwave integrated-circuit/monolithic-microwave integrated-circuit applications. The proposed design technique can produce a coupler with flat coupling over 50% fractional bandwidth, which is wider than the conventional lumped-element design methods. A prototype consisting of a capacitive coupled high-pass network is designed and fabricated to verify the design concept. Measurement and simulation results closely correspond to each other.

Transdirectional Coupled-Line Couplers Implemented by Periodical Shunt Capacitors

Transdirectional coupled-line couplers have the benefit of perfect input/output isolation. However, for a coupled-line coupler to operate in transdirectional mode, both phase- and impedance-coupling are required, which is difficult to meet by traditional coupled lines. To overcome this problem, this paper presents a novel transdirectional coupled-line coupler implemented by periodically loaded coupled lines. Two 3-dB 90° hybrids are designed and built to verify this concept. The first one was built on FR-4 substrates and operated at 3.6 GHz. The second one was built on Roger RT/Duroid 5870 substrates with length reduced and operated at 3.6 GHz. A good agreement with simulated results is reached.

Low Phase-Noise and Low-Power CMOS VCO Constructed in Current-Reused Configuration

A Ku-band CMOS voltage-controlled oscillator (VCO) constructed in a modified current-reused configuration is presented in this letter. Two dc level shifters combined into two metal-insulator-metal capacitors are adopted to solve the transconductance and load mismatch problems of the conventional current-reused VCO for obtaining more symmetrical oscillation signals and lowering the phase noise of oscillator. A prototype was designed and measured to verify the design concept. The measurement results demonstrate the central oscillation signal of 16 GHz to be associated with the 900 MHz tuning range and -111 dBc/Hz phase noise at 1 MHz offset. The power consumption of the VCO core is only 8.1 mW. The measurement result evaluated by means of a figure of merit is about -186.8 dBc/Hz.

A new compact LTCC bandpass filter using negative coupling

This letter presents the design and realization of a new compact bandpass filter (BPF) fabricated on multilayered ceramic substrates. This BPF features coupled resonators with negative coupling coefficients. A BPF with center frequency 2.45 GHz is designed and fabricated. Its size is only 2.0 mm/spl times/1.8 mm/spl times/0.67 mm when implemented by a standard low temperature co-fired ceramic technology. The size reduction is due to the higher coupling coefficient between the negatively-coupled resonators than the positively-coupled ones, allowing tighter space between the resonators. The measured insertion losses of the previous BPF were less than 3dB and return losses more than 18dB in the passband. The measured result agrees very well with the electromagnetic (EM) designed response.

Design of microwave wide-band quadrature hybrid using planar transformer coupling method

A lumped-element quadrature hybrid consisting of two-section inductive coupled /spl pi/-networks is presented. A synthesizing method involving a new set of design equations are also developed to realize the proposed hybrid with very good balance in both magnitude and phase between the output ports over a 38% fractional bandwidth. The measurements of the two prototypes show quite good agreement with the theoretical predictions. The proposed hybrid is compact and suited to be implemented by conventional microwave-integrated-circuit technology.

Microstrip Diplexer Constructed With New Types of Dual-Mode Ring Filters

-A microstrip diplexer consisting of two new types of ring filters is presented in this letter. The proposed ring filter is able to move one of transmission zeros closer to its passband corner by connecting the feeding capacitors at the different locations of the resonant ring. Thus, a diplexer implemented by connecting two kinds of ring filters with different feeding features can achieve the required isolation for the small channel separation. Then an open-stub is added at the common input port of the channel filters to achieve the required input matching at the two passbands of the diplexer. A diplexer prototype with two passbands at 1.75 GHz and 1.85 GHz with a channel separation 40 MHz was fabricated. The measured insertion losses in the pass bands are all less than 2.1 dB. The isolation between the two channels is greater than 20 dB and the input return losses of the three ports are about 20 dB.

Analysis and Design of a Chip Filter With Low Insertion Loss and Two Adjustable Transmission Zeros Using 0.18-

This paper presents the structure of a high-selectivity bandpass filter that is fabricated on low-resistivity silicon substrate with a commercial CMOS technology. The filter is constructed using crossed coplanar waveguide (CPW) lines and metal-insulator-metal capacitors to ensure that it has the desired passband characteristics. An adjustable capacitor between the input and output ports is employed to form a capacitive cross-coupled path, yielding two transmission zeros in the lower and upper stopbands, respectively. Additionally, the coupling mechanism can be modified by turning on or off the gate of an nMOS transistor to adjust the positions of the transmission zeros by applying an externally controlled voltage. To obtain a low passband loss and to minimize the chip size, high-impedance CPW transmission lines are adopted. Our analysis indicates that the CPW line possesses more advantages than the preferred stacked-ground CPW line for constructing the proposed filter. A very compact X -band experimental prototype with a size of 0.88 × 0.54 mm2 was designed and fabricated. The measurements reveal an insertion loss of less than 3.2 dB in the passband, which is from 10.6 to 12.7 GHz, and rejection levels greater than 35 dB at the designed frequencies of transmission zeros. Moreover, the lower and upper transmission zeros can be shifted from 5 to 6.5 GHz and from 18 to 21.4 GHz, respectively, by changing the controlled voltage.

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This paper presents a new method of designing tightly coupled directional couplers on printed circuit board substrates. The coupler is realized by placing a piece of floating metal plate on parallel-coupled microstrip lines to enhance the coupling between the lines. This structure yields a tightly coupled directional coupler without wire bonding and using high-resolution fabrication processes. A design procedure based on closed-form design equations of the parallel-coupled microstrips is proposed to design the new coupler. An S-band 3-dB coupler constructed from the new structure is fabricated and measured to verify the proposed design procedure. Another wideband coupler, comprising two sections of conventional microstrip couplers and one section of the new type coupler, is also fabricated and measured to demonstrate the flexibility of connecting the new structure and conventional microstrip structures or devices. The measurements of the two couplers demonstrate that the coupler operates properly with approximately 54% and 94% fractional bandwidth, respectively, showing good agreement with the electromagnetic simulations. Additionally, a broadband filter consisting of four sections of the proposed coupling structure is fabricated and tested. The measured insertion losses are around 0.8 dB associated with return losses of greater than 15 dB over a frequency range of 4.5-7.1 GHz, corresponding to a fractional bandwidth of 45%.

CMOS Technology

A compact open-loop resonator with multispurious suppression is proposed. When excited symmetrically, the resonator shows two tunable transmission zeros. By adjusting the open-end gap capacitance, one of the zeros is placed near the passband and the other is tuned to collocate with the leading two degenerated higher order resonances, so that the circuit has a sharp transition as well as a wide upper stopband. The experimental circuit shows the first spurious peak occurs at four times the passband frequency (4fo), and the measurement shows good agreement with the theoretic prediction.

Closed-Form Equations of Conventional Microstrip Couplers Applied to Design Couplers and Filters Constructed With Floating-Plate Overlay

This study presents a Ku-band band-pass filter designed and fabricated with a commercial CMOS technology. The filter utilizes a pi-network coupling structure to construct the desired coupling and the resonant tanks on Si substrate with a compact size and the low-loss performance. A method of synthesizing pi-network filter is proposed. A 17GHz filter chip was fabricated by 0.18mum CMOS technology. The size of filter is 0.56mmtimes0.6mm and the measured pass-band insertion loss of filter is about 3.2dB