Performance of Arrays of SIS Junctions in Heterodyne Mixers

We have made a systematic experimental study of the performance of millimeter-wave quasiparticle heterodyne mixers which use arrays of SIS tunnel junctions. Sets of arrays with N =1, 5, 10, 25, and 50 junctions in series were fabricated by photolithography. All of the arrays in a given set were made on a single silicon wafer so that their response time parameter omega/sub S/R/sub N/C would be the same. Junction areas were scaled so that the total impedance was the same for each array in a set. Sets of arrays from four wafers with values of omega/sub S/R/sub N/C ranging from 2.6 to 13 were evaluated in mixers at 33 and 36 GHz. These measurements showed that the signal power required to saturate the mixers varies as N/sup 2/ and that the conversion efficiency is nearly independent of N for all values of omega/sub S/R/sub N/C. The mixer noise temperature is independent of N for large values of omega/sub S/R/sub N/C. Therefore, the dynamic range of an SIS quasiparticle mixer can increase in proportion to N/sup 2/. For small values of as omega/sub S/R/sub N/C, however, the mixer noise increases systematically with N. This correlation suggests that the junction capacitance affects the coupling between junctions that can contribute to the noise.     

A Novel LO Power Injection Method for SIS Mixers

We propose a novel LO power injection method developed for SIS mixers in this paper. Based on the feature of extremely small LO power requirements of SIS quantum mixing, the new method fulfills SIS pumping through a DC/IF route based built-in LO path, which is composed of an additional LO waveguide and the existing microstrip choke filter on the junction substrate. With the new method, traditional external LO diplexers(e.g., crossguide-couplers or beamsplitters) become unnecessary, resulting in a lower loss, compact, and stable receiver system. Experiments at 110- and 230 GHz bands have shown that the present method is efficient in coupling sufficient pumping power to SIS junctions from general LO sources, and the receiver sensitivities have a further improvement of about 10 K. We expect this method is also able to be applied into submillimeter wave band for SIS mixers.     

Simulation of Sub-harmonic SIS Mixers with a Full Five-Port Model

The performance of superconductor-insulator-superconductor (SIS) sub-harmonic mixers is thoroughly investigated in this paper. On account of the importance of the harmonic effect, a full five-port model combined with an enhanced Newton solution is applied to calculate the local oscillator (LO) waveform. The mixer performance is studied as functions of principal parameters including the embedding admittances, LO power and bias voltage. The results are compared with those from the quasi five-port model.     

A Novel Circuit Architecture for High Performance of High-order Subharmonic Mixers

A novel circuit architecture for high performance of high-order subharmonic (SH) mixers is proposed in this paper. According to the specified harmonic mixing order, one or more mixer diodes sub-arrays and corresponding power divider as well as phase shift network for RF and LO signals are arranged in the circuit. This proposed SH mixer circuit has improved conversion loss, wide dynamic range and high port isolation for high-order SH mixers. By phase cancellation of idle frequencies, the proposed SH mixer circuit can eliminate complicated design procedure of idle frequency circuits; by phase cancellation of leakage LO power to RF and IF port, and leakage RF power to LO port, the mixer circuit can get high port isolation in LO-IF/RF and RF-LO. The increased antiparallel diode pairs in each sub-array will also lead to well performance by lowering effective series resistance. The proposed SH mixer circuit can be easily realized with power divider and phase shift network for RF and LO signals.     

一种新型跨导-电容滤波器自调谐电路

提出了一种基于开关电容技术的跨导一电容(Gm-C)滤波器自调谐电路.与基于压控振荡器(VCO)和压控滤波器(VCF)的传统调谐电路不同,该自调谐电路具有更高的精度和更低的功耗,且电路结构简单.设计了一个9阶椭圆函数低通滤波器,通过该调谐电路,实现了截止频率的精确可调.     

一种Gm-C复数滤波器频率调谐电路

采用TSMC 0.25μm CMOS工艺,设计了一个Gm-C复数滤波器的频率调谐电路。基于PLL锁相技术,利用工作于深线性区的NMOS管和MiM电容组成的环形振荡器检测频率参数偏差,并自动调谐到希望值。仿真和测试结果表明,该电路能将频率偏差降低到3%以下。     

Low-Loss NbTiN Films for THz SIS Mixer Tuning Circuits

Recent results at 1 THz using normal-metal tuning circuits have shown that SIS mixers can work well up to twice the gap frequency of the junction material (niobium). However, the performance at 1 THz is limited by the substantial loss in the normal metal films. For better performance superconducting films with a higher gap frequency than niobium and with low RF loss are needed. Niobium nitride has long been considered a good candidate material, but typical NbN films suffer from high RF loss. To circumvent this problem we are currently investigating the RF loss in NbTiN films, a 15K Tc compound superconductor, by incorporating them into quasi-optical slot antenna SIS devices.     

Equivalent Circuit for Partially Dielectric-Filled Rectangular-Waveguide Junctions

The problem of electromagnetic-wave propagation in junctions between two symmetrically, partially dielectric-filled waveguides was investigated, and the solution is presented in the form of a two-port equivalent circuit, This equivalent circuit includes an ideal 1:1 transformer, which is connected to transmission lines with impedances equal to those of the two waveguides, in cascade with a T network. Elements of the T network and the characteristic wave impedances of these partially dielectric-filled waveguides have been studied, and the results are presented in graphs for different dielectric constants, slab thicknesses, and operating frequencies.     

A Dual Mode Tuning Circuit for Microwave Transistor Oscillators

A two-port circuit adjusting both even and odd mode fields, with orthogonal mode adjustment, can be used as an embedding circuit for a microwave transistor oscillator. The circuit, analyzed in TEM line, may also be realized in any other form of transmission line geometry, including two coexistent modes in a cavity. The resulting oscillator is stable, has low FM noise, and is readily tunable. Analyses of the tuning circuit and oscillator are presented, along with some experimental results and a discussion of methods using other than TEM transmission lines to produce the even and odd modes.     

Design Consideration for a Two-Distributed-Junction Tuning Circuit

We describe a novel method of designing a tuning circuit with two half-wave distributed junctions separated by a half-wavelength microstripline, which analytically determines the circuit parameters such as the minimum current density of the junctions and the characteristic impedances of the distributed junctions and the microstripline. The tuning circuit was approximated by simple transmission theory and then simplified with ideal circuit components for analysis. We applied Chebyshev’s band-pass filter theory, in part, to optimize the circuit design. The analytical results revealed that a high characteristic-impedance ratio between the distributed junctions and the microstripline is necessary to obtain broadband matching using low-current-density junctions. The experimental results for all-NbN SIS mixers we designed with this method demonstrated double-sideband (DSB) receiver-noise temperatures of 6–10 quanta from 710 to 810 GHz for a mixer with a current density of only 4 kA/cm² (estimated ωC_JR_N product of 37 at 750 GHz). The RF bandwidth was broader than that of a conventional full-wave distributed SIS mixer with the same current density.     

A Low-Noise 230 GHz SIS Receiver for Radio Astronomy Employing Untuned Nb/AlOx/Nb Tunnel Junctions

A heterodyne receiver based on a ～1/3 reduced height rectangular waveguide SIS mixer with two mechanical tuners has been built for astronomical observations of molecular transitions in the 230 GHz frequency band. The mixer used an untuned array (ωR_nC_j≈3, R_n≈70 Ω) of four Nb/AIOx/Nb tunnel junctions in series as a nonlinear mixing element. A reasonable balance between the input and output coupling efficiencies has been obtained by choosing the junction number N=4. The receiver exhibits DSB (Double Side Band) noise temperature around 50 K over a frequency range of more than 10 GHz centered at 230 GHz. The lowest system noise temperature of 38 K has been recorded at 232.5 GHz. Mainly by adjusting the subwaveguide backshort, the SSB (Single Side Band) operation with image rejection of ≥ 15 dB is obtained with the noise temperature as low as 50 K. In addition, the noise contribution from each receiver component has been studied further. The minimum SIS mixer noise temperature is estimated as 15 K, pretty close to the quantum limit ?v/k～11 K at 230 GHz. It is believed that the receiver noise temperatures presented are the lowest yet reported for a 230 GHz receiver using untuned junctions.     

A Simple Tuning Circuit for Waveguide and Transmission Line Systems (Correspondence)

A simple tuning circuit for source or load matching is described that makes possible smooth and sensitive adjustments with no "holes" in frequency coverage over a complete waveguide band. Energy is coupled out of the mainline, the phase and magnitude adjusted with phase shifter and attenuator and fed back into the mainline to cancel the reflected signal. A simple analysis of the circuit is presented, and a graph given for estimating the maximum voltage standing-wave (VSWR) that can be "tuned out." Application to measurement of reflection coefficient or to impedance is proposed.     

一种基于分布式放大器的MASK调制电路

基于0.18 μm CMOS工艺设计了一种工作在10 GHz的八进制幅移键控调制电路.利用分布式放大器的结构特点,通过增加一组开关来改变信号传输路径,控制输出信号的振幅和相位,实现了信号的八进制幅移键控调制,有效提高了信号传输的频带利用率.仿真结果表明,该调制电路在载波频率为10 GHz时,数据率可达3 Gbit/s,...     

A Modulator for Microwave Mixers (Correspondence)

A method is described for producing an amplitude modulated wave at an intermediate frequency from the mixing of two cw signals in a coaxial or waveguide system. The method is adaptable to any frequency range in which crystal mixers are used. At least 82 per cent modulation is produced by this method, and the envelope is a square wave. The repetition rate is 0 to 20 kc with presently available commercial components.     

片上锁相环调谐的低功耗中频复数滤波器设计

讨论了应用于IEEE802.15.4标准低中频接收机的3阶贝塞尔复数gm-C滤波器,其中跨导器采用Nauta结构.为了消除工艺偏差、温度变化、老化对截止频率的影响,滤波器电路使用了片上锁相环调谐电路.滤波器设计采用HJTC-0.18 μm 1P6M CMOS混合工艺,中心频率为 3 MHz,-3 dB带宽为2.6 MHz.仿真结果显示临道、间道抑制分别为26.4、44 dB,镜像抑制为31.4 dB,带内SFDR为54.8 dB.复数滤波器电源电压为2.5 V,整体消耗的电流约为1.61 mA.     

A Fast-Speed Pulse Detector Based on N-Type Si-Schottky Diode via Tuning Circuit

A fast-speed pulse detector based on n-type Si-Sehottky diode mounted in the waveguide is investigated. The relation of the fast-speed pulse detector between response time and 3 dB bandwidth is analyzed. By adopting the tunable circuit, the matched bandwidth is achieved as wide as possible. Experi- mental results show that the pulse response time of the detector is less than 150 ps within random carrier signal 500 MHz bandwidth range between 35 GHz to 39 GHz via tuning circuit. The detector is very easy to operate because it does not need bias current or synch-pulse source.     

A New IIP2 Enhancement Technique for CMOS Down-Converter Mixers

The design of a CMOS mixer for cellular phone and 3G applications is challenging because of tough linearity and noise requirements. A new technique for second-order input intercept point (IIP2) enhancement of CMOS down-converter mixers is introduced in this brief. The technique is based on canceling second-order intermodulation components generated in input pseudodifferential transconductor, by injecting a nonlinear current to the mixer. Since this current is controlled by a high bandwidth feedback loop, the cancellation technique can be used in multistandard mixers for high channel bandwidth applications like UMTS and IEEE802.11 as well as GSM. A CMOS mixer demonstrating the performance for UMTS standard is designed in a 65-nm technology which can work with supplies as low as 1 V. The simulation results show that the differential and common mode IIP2 of the mixer are improved about 22 and 29 dB, respectively, while cancellation circuit consumes less than 3.3 mA. The other mixer parameters such as noise figure are not affected by the proposed technique.     

A Short Rugged Ferrite Half-Wave Plate for a Single-Sideband Modulator (Correspondence)

One type of microwave phase shifter consists of two quarter-wave plates between which is placed a half-wave plate whose principal axis is rotatable. The phase shift introduced is directly proportional to the angular displacement of the principal axis of the half-wave plate. Continuous rotation of the principal axis causes continuous advancement or retardation of the phase of the signal traversing the phase shifter. This causes a frequency shift of the signal and the device can thus be used as a single-sideband modulator.     

A 345GHz SIS receiver for radio astronomy

A 345GHz superconductor insulator superconductor (SIS) tunnel junction receiver utilizing a full height rectangular waveguide mixer with two tuning elements, i.e. an E-plane and backshort tuner, has been constructed and installed on the Caltech Submillimeter Observatory 10m antenna on Mauna Kea, Hawaii. The receiver exhibits a best double side-band noise temperature response of 150K±20K (averaged over a 500 MHz IF bandwidth centered at 1.5GHz) at a design center frequency of 345GHz and at an ambient temperature of approximately 3.8K. Additional measurements show that the receiver has an excellent response at selected points within an RF input range of 280 to 363GHz.