Passive Mixer Research Articles

Numerical Investigation of Liquid–Liquid Mixing in Modified T Mixer with 3D Obstacles

The fluids inside passive micromixers are laminar in nature and mixing depends primarily on diffusion. Hence mixing efficiency is generally low, and requires a long channel length and longtime compare to active mixers. Various designs of complex channel structures with/without obstacles and three-dimensional geometries have been investigated in the past to obtain an efficient mixing in passive mixers. This work presents a design of a modified T mixer. To enhance the mixing performance, circular and hexagonal obstacles are introduced inside the modified T mixer. Numerical investigation on mixing and flow characteristics in microchannels is carried out using the computational fluid dynamics (CFD) software ANSYS 15. Mixing in the channels has been analyzed by using Navier–Stokes equations with water-water for a wide range of the Reynolds numbers from 1 to 500. The results show that the modified T mixer with circular obstacles has far better mixing performance than the modified T mixer without obstacles. The reason is that fluids' path length becomes longer due to the presence of obstacles which gives fluids more time to diffuse. For all cases, the modified T mixer with circular obstacle yields the best mixing efficiency (more than 60%) at all examined Reynolds numbers. It is also clear that efficiency increase with axial length. Efficiency can be simply improved by adding extra mixing units to provide adequate mixing. The value of the pressure drop is the lowest for the modified T mixer because there is no obstacle inside the channel. Modified T mixer and modified T mixer with circular obstacle have the lowest and highest mixing cost, respectively. Therefore, the current design of modified T with circular obstacles can act as an effective and simple passive mixing device for various micromixing applications.

Simple structured and highly efficient passive T‐type micromixer with circumferential in‐step at entry

AbstractMany micromixing applications require simple structured passive mixers rather than complex structured passive or expensive active mixers. However, mixing quality in a typical simple structured passive mixer remains poor. In the present work, simple T‐type micromixer is modified with a circumferential in‐step at the entry of inlet channels to generate velocity components oblique to the mainstream inlet flow. The performance of T and T–T mixers with and without circumferential in‐step has been estimated for various Re (0 to 700). Results showed that inlet sample flow achieved velocity components of three‐dimensional nature with circumferential in‐step, leading to a momentous degree of intertwinement and entanglement of samples during the collision at the confluence of inlet channels. As a result, a remarkable improvement in mixing is obtained in the presence of in‐step for sufficiently higher flow rates of Re above 100 by T‐mixer and Re above 300 by T–T mixer. In particular, T‐mixer offers better advantage with in‐step compared to T–T mixer; marking an improvement for Re as low as 100 and above, as well as exhibiting shorter mixing lengths. Therefore, the present design of simple structured T‐mixer with in‐step at entry can be an effective device for various micromixing applications.

Analysis of Non-Idealities on CMOS Passive Mixers

In the current state of the art, WiFi-alike standards require achieving a high Image Rejection Ratio (IRR) while having low power consumption. Thus, quadrature structures based on passive ring mixers offer an attractive and widely used solution, as they can achieve a high IRR while being a passive block. However, it is not easy for the designer to know when a simple quadrature scheme is enough and when they should aim for a double quadrature structure approach, as the latter can improve the performance at the cost of requiring more area and complexity. This study focuses on the IRR, which crucially depends on the symmetry between the I and Q branches. Non-idealities (component mismatches, parasitics, etc.) will degrade the ideal balance by affecting the mixer and/or following/previous stages. This paper analyses the effect of imbalances, providing the constraints for obtaining a 40 dB IRR in the case of a conversion from a one-hundred-megahertz signal to the five-gigahertz range (upconversion) and vice versa (downconversion) for simple and double quadrature schemes. All simulations were carried out with complete device models from 65 nm standard CMOS technology and also a post-layout Monte Carlo analysis was included for mismatch analysis. The final section includes guidelines to help designers choose the most adequate scheme for each case.

Mm-Wave Mixer-First Receiver With Selective Passive Wideband Low-Pass Filtering

The front-end of a conventional millimeter-wave receiver (RX) consists of a bandpass filter (BPF) and low-noise amplifier (LNA) prior to the frequency down-conversion mixer. In interference-limited wireless channels, it is more footprint and power efficient to remove the BPF and LNA, and realize the mixer as a “passive” switching scheme. The noise figure of this passive mixer-first RX is improved when numerous such RXs are placed in a phased array or multi-input multi-output (MIMO) configuration. The passive switching mixer can be followed with an on-chip selective passive low-pass filter (LPF) with a small footprint given the large channel bandwidth that is typical in mm-wave applications. In this article, system and circuit design aspects of mm-wave passive mixer-first RXs are discussed and validated by a proof-of-concept 65-nm CMOS prototype. The implemented RX operates in the 21-29-GHz frequency range with 0.5-GHz instantaneous single-sideband (SSB) bandwidth, and achieves stopband to passband rejection of >49 dB, an in-band ICP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1 dB</sub> of -6 dBm, and out-of-band B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1 dB</sub> > 3.4 dBm.

A 28-GHz Bidirectional Active Gilbert-Cell Mixer in 90-nm CMOS

A bidirectional active mixer based on Gilbert-cell topology is proposed and realized in 90-nm CMOS at 28 GHz. The offered mixer can achieve both the up- and down-conversion under 1-dBm local oscillator (LO) power by adjusting the Gilbert quad switch's gate bias. An IF bidirectional amplifier (IFBDA) is adapted to compensate for the conversion loss (CL) of the Gilbert quad switch. The measured peak conversion gain (CG) is -2.14/-3.28 dB at 28-GHz, and the 3-dB bandwidth is 7/6 GHz in transmit (Tx)/receive (Rx) mode. Total dc power consumption is only 8.4/6.4 mW for Tx/Rx mode under 1.2-V supply voltage. Compared with the traditional bidirectional passive mixers, this mixer demonstrates a low CL with a low LO power.

A Godunov-Type Stabilization Scheme for Large-Signal Simulations of a THz Nanowire Transistor Based on the Boltzmann Equation

A stabilization method is presented for the Boltzmann equation (BE) that is based on Godunov’s approach applied directly in the phase space. This makes it possible to perform transient simulations under quasiballistic conditions and to include the Pauli principle in the scattering integral without further approximations. The method ensures positive distribution functions by construction. The BE is solved self-consistently together with the Poisson and Schrodinger equations by the Newton–Raphson method for a nanowire silicon nMOSFET, for which the stationary ${I}$ – ${V}$ characteristics, the small-signal admittance parameters, and the switching behavior are calculated. The large-signal behavior of the MOSFET as an amplifier is evaluated by cyclostationary simulations including power gain and the output power at higher harmonics. The current responsivity of the MOSFET operated as a passive mixer is simulated up to terahertz (THz) frequencies including the quasiballistic case with negligible scattering.

A wideband subharmonic passive image rejection mixer

This article presents a circuit topology for a wideband subharmonic image rejection mixer. The mixer circuit is realized by employing two identical subharmonic mixers based on Schottky antiparallel diode pair, a wideband 90° differential phase shifter and a band pass filter without involving bonding wires, high impedance or tightly coupled arms. To demonstrate the topology, a mixer with 1 GHz as the fixed intermediate frequency is fabricated for 6 to 10 GHz of RF frequency. The lower side band is considered as the undesired band. Measurement results exhibit a minimum conversion loss of 7.87 dB and a maximum image rejection ratio of 41 dB at a local oscillator drive level of 9 dBm. Measured 1 dB compression point is 3 dBm. There is no requirement of DC bias.

Review of FET Ring mixer topologies for wireless communication

This paper presents an important component of the radio frequency transceiver called as mixer. It is a critical component and plays an important role as it has the ability for frequency conversion in RF systems. This paper focuses on double balanced ring topology of passive mixers. Ring mixer is one of the best example of passive mixers because of double balanced in nature. Double balanced is one of the most widely used topology as it suppresses both LO and RF at the output the of mixer. Various techniques have been used to improve the performance of standard topology of the ring mixer such as noise figure, linearity, conversion gain and port isolation, so these techniques have been re-viewed and compared with the previous studies. This paper also have brief discussion about a useful passive circuitry say balun and its designing with mixer as this is generally used to convert single ended signal to differential signal.

Frequency-Domain-Multiplexing Single-Wire Interface and Harmonic-Rejection-Based IF Data De-Multiplexing in Millimeter-Wave MIMO Arrays

Recently, mm-wave multi-in multi-out (MIMO) arrays are garnering significant attention because of their ability to form multiple spatial beams, achieving significantly higher data rates compared to traditional phased array-based approaches. Furthermore, scalable MIMO arrays can provide many other functionalities, such as full digital beamforming and per-power amplifier (PA) digital pre-distortion. In this work, an MIMO four-element TX array architecture is presented with a frequency-domain multiplexing-based single-wire interface (SWI), breaking the tradeoff between channel-to-channel isolation and single wire (SW) bandwidth (BW). The concept of harmonic-rejection mixing (HRM) is used to de-multiplex the four modulated signals simultaneously from the SW using a single passive mixer driven by a multi-phase local oscillator (LO). The two-stage harmonic recombination circuits are implemented in baseband and, hence, achieve high channel-to-channel isolation with a low power overhead. A 60-GHz four-element TX prototype demonstrates the proposed architecture in 45-nm RF silicon-on-insulator (RFSOI) CMOS. The frequency-division-multiplexed (FDM)-based SWI can support 8-GHz total intermediate frequency (IF) BW across the four channels with 30-40-dB channel-to-channel isolation. Each TX element in the array achieves 20-35-dB conversion gain and +8.8-10.9-dBm OP1dB while consuming 225 mW/element.

A Passive-Mixer-First Acoustic-Filtering Superheterodyne RF Front-End

This article presents an agile passive-mixer-first superheterodyne RF front-end that utilizes a gigahertz acoustic filter as its intermediate-frequency (IF) load—essentially a mixer-first acoustic-filtering RF front-end . The passive mixer frequency-translates a sharp but fixed-frequency acoustic-filtering response to a much higher and mixer-clock-defined tunable frequency while preserves input matching, high linearity, and introduces minimal loss. In contrast to low- or zero-IF passive-mixer-first receivers which often use active filters at baseband, using an acoustic filter as the IF load is fraught with fundamental challenges. We introduce ON-chip LC tanks, as an impedance shaper , to suppress the acoustic filter impedance components at harmonic frequencies and an all-passive recombination network at IF to share one acoustic filter among multiple paths. Also, we extend the existing analysis of mixer-first front-ends from assuming a load impedance with a low-pass frequency response to having a generic load impedance. Our analysis unveils impedance aliasing in a generic mixer-first front-end, motivating the need for an ON-chip impedance shaper. A front-end prototype using a 65-nm CMOS switched- LC passive mixer followed by an off-the-shelf 1.6-GHz surface-acoustic-wave (SAW) filter is designed. In measurement, the RF front-end operates across 2.5-to-4.5 GHz achieving 5.5-dB noise figure and +29.4-dBm IIP3 at 1 $\times $ bandwidth offset.

Kinematic Measurements of Novel Chaotic Micromixers to Enhance Mixing Performances at Low Reynolds Numbers: Comparative Study.

In this work, a comparative investigation of chaotic flow behavior inside multi-layer crossing channels was numerically carried out to select suitable micromixers. New micromixers were proposed and compared with an efficient passive mixer called a Two-Layer Crossing Channel Micromixer (TLCCM), which was investigated recently. The computational evaluation was a concern to the mixing enhancement and kinematic measurements, such as vorticity, deformation, stretching, and folding rates for various low Reynolds number regimes. The 3D continuity, momentum, and species transport equations were solved by a Fluent ANSYS CFD code. For various cases of fluid regimes (0.1 to 25 values of Reynolds number), the new configuration displayed a mixing enhancement of 40%–60% relative to that obtained in the older TLCCM in terms of kinematic measurement, which was studied recently. The results revealed that all proposed micromixers have a strong secondary flow, which significantly enhances the fluid kinematic performances at low Reynolds numbers. The visualization of mass fraction and path-lines presents that the TLCCM configuration is inefficient at low Reynolds numbers, while the new designs exhibit rapid mixing with lower pressure losses. Thus, it can be used to enhance the homogenization in several microfluidic systems.

Comparison of active dual‐gate and passive mixers for terahertz applications

The authors propose four versions of a dual-gate active down-conversion mixer for H-band applications. The mixer operates at a local oscillator (LO) frequency of 240 GHz. It is designed for maximum conversion gain and a large bandwidth of at least 50 GHz from 220 to 270 GHz. Furthermore, the mixer is .optimised to operate at low LO power levels beneath 0 dBm. This renders power hungry LO buffer stages redundant. Hereby, the necessary chip size and the overall power consumption of fully integrated receivers can be drastically reduced. Four different versions of the downconverter were designed. Firstly, the layout of the transistors was changed from a conventional multi-transistor cell design to a mixer topology within the multi-finger transistor cell. Secondly, two on-chip solutions to decouple the drain voltage from the intermediate frequency (IF) signal were realised to facilitate zero-IF conversion: a resistive and an active load. The results are presented and the advantages and disadvantages of the four versions for the usage in terahertz applications are thoroughly analysed. Finally, the active dual-gate mixers are compared to a state-of-the-art resistive mixer for H-band with regard to conversion gain, bandwidth, linearity, noise figure and chip size.

A 4.8-dB NF, 440-μW Bluetooth Receiver Front-End With a Cascode Noise Canceling LNTA

An ultralow power (ULP) low-noise receiver front-end for the BLE application is presented in this letter. The tradeoff between noise and power consumption is mitigated by employing a transformer-based passive $g_{m}$ -boosting common-gate low noise transconductance amplifier (LNTA). Local-positive feedback (LPF) and feedforward (FF) noise cancellation techniques are combined in the LNTA to further lower noise. After the passive mixer, a TIA implements complex filtering with a moderate conversion gain. The receiver front-end, fabricated in TSMC 28-nm process, consumes only $440~\mu \text{W}$ under 0.9-V supply with a minimum noise figure of 4.8 dB.

A wideband receiver front-end with low noise and high linearity by exploiting reconfigurable dual paths in 180 nm CMOS

In this paper, a wideband receiver front-end including the flexible reconfigurable main and auxiliary paths is proposed. Therein, the main path has the low-noise advantage thanks to the low-noise transconductance amplifier (LNTA) preceding the mixer and baseband. Meanwhile, by utilizing a mixer-first structure, the auxiliary path renders a high in-band and out-of-band linearity. Furthermore, an inductor resonance structure is also designed to mitigate the baseband noise crosstalk issue which is disclosed by a charging/discharging mechanism via the tail capacitance of passive mixers. Both of the receiving paths have shared a common baseband circuit while loading a commonly-shared 25% duty-cycle LO source generator. Simulation results by a 180 nm CMOS have demonstrated that the main path provides a low noise figure (NF) of 2.7 dB, while the auxiliary path obtains the in-band and out-of-band IIP3 of 9.2 and 21 dBm under typical LO excitation frequency of [Formula: see text] GHz. The power consumption of the main path of the dual-path front-end is 57 mW and that of the auxiliary path is 26 mW under a supply voltage of 1.8 V.

Antisolvent based ultrasound-assisted batch and continuous flow precipitation of metformin hydrochloride particles

Small sized particles of the antidiabetic drug metformin hydrochloride (MET.HCl) were produced by antisolvent based precipitation using an ultrasound assisted inverted jet reactor (IJR). This novel approach was implemented as a small passive mixer in which intensified turbulent mixing of the solution and the antisolvent occurred under controlled conditions. The optimized conditions for antisolvent precipitation (ASP) were investigated by studying the effect of solute concentration, antisolvent to solvent ratio and antisolvent temperature in batch systems. The optimized batch precipitation conditions were successfully translated into continuous flow process for the ultrasound assisted inverted jet reactor. The ability of the proposed clogging free inverted jet reactor approach can provide a scaled up alternative pathway to micro and millifluidic devices for manufacturing of small sized API particles, such as, MET.HCl for the formulations and encapsulations on an industrial scale.

425-to-25-GHz CMOS-Integrated Downconverter

An integrated 425-GHz radio frequency (RF) to 25-GHz intermediate frequency (IF) second-order subharmonic downconverter, including an on-chip 8X local oscillator (LO) signal multiplier circuit that provides ~1 dBm at 200 GHz from an externally applied 25-GHz signal, and a 25-GHz IF amplifier, achieves a conversion gain of 6.7 dB and a noise figure of ~17 dB. The downconverter consumes 190 mW of dc power. Compared to the previously reported CMOS and SiGe HBT receivers/downconverters operating around 400 GHz and above, the downconverter achieves ~18-dB lower single side band noise figure. Finally, a passive switching mixer can have an available output noise spectral density less than kT, which can make its NF less than its conversion loss.

Optimized design of obstacle sequences for microfluidic mixing in an inertial regime.

Mixing is a basic but challenging step to achieve in high throughput microfluidic applications such as organic synthesis or production of particles. A common approach to improve micromixer performance is to devise a single component that enhances mixing through optimal convection, and then sequence multiple such units back-to-back to enhance overall mixing at the end of the sequence. However, the mixing units are often optimized only for the initial non-mixed fluid composition, which is no longer the input condition for each subsequent unit. Thus, there is no guarantee that simply repeating a single mixing unit will achieve optimally mixed fluid flow at the end of the sequence. In this work, we analyzed sequences of 20 cylindrical obstacles, or pillars, to optimize the mixing in the inertial regime (where mixing is more difficult due to higher Péclet number) by managing their interdependent convection operations on the composition of the fluid. Exploiting a software for microfluidic design optimization called FlowSculpt, we predicted and optimized the interfacial stretching of two co-flowing fluids, neglecting diffusive effects. We were able to quickly design three different optimal pillar sequences through a space of 3220 possible combinations of pillars. As proof of concept, we tested the new passive mixer designs using confocal microscopy and full 3D CFD simulations for high Péclet numbers (Pe ≈ O(105-6)), observing fluid flow shape and mixing index at several cross-sections, reaching mixing efficiencies around 80%. Furthermore, we investigated the effect of the inter-pillar spacing on the most optimal design, quantifying the tradeoff between mixing performance and hydraulic resistance. These micromixer designs and the framework for the design in inertial regimes can be used for various applications, such as lipid nanoparticle fabrication which has been of great importance in vaccine scale up during the pandemic.

2.4 GHz BLE Receiver With Power-Efficient Quadrature RF-to-Baseband-Current-Reuse Architecture for Low-Power IoT Applications

In this paper, a 2.4 GHz Bluetooth low energy receiver employing a power-efficient quadrature RF-to-baseband-current-reuse architecture is presented for low-power low-voltage internet of things applications. The proposed quadrature RF-to-baseband-current-reuse RF front-end consists of a low-noise transconductance amplifier, an active-type polyphase filter-based quadrature generator, transimpedance amplifiers, and double-balanced current-mode passive mixers on a single dc current path. An input matching network is used to perform power-constrained simultaneous noise and input power matching and 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f$ </tex-math></inline-formula> noise reduction in the RF and baseband domains, respectively. The quadrature RF signals are provided to the single-quadrature mixers through an embedded active-type polyphase filter-based quadrature generator. The implemented Bluetooth low energy receiver is composed of the RF-to-baseband-current-reuse RF front-end, IF amplifiers, two-stage passive- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> polyphase filter, and fifth-order Chebyshev-II <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G_{m}$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-C</i> filters. The proposed design was fabricated using a 65-nm CMOS process and characterized primarily in the Bluetooth low energy operating frequency bands. The active die area of the implemented receiver was 0.85 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the receiver drew a bias current of 1.41 mA from a nominal supply voltage of 0.8 V. The Bluetooth low energy receiver achieved a noise figure of 13.2 dB, conversion gain of 42 dB, image rejection ratio of more than 30 dB, and input-referred third-order intercept point of −25 dBm.

A 50-Gb/s Compact RadCom E-Band Transmitter With Phase-Controlled Push–Push Quadrupler and Stacked-FET Power Amplifier

We present a 66–79-GHz transmitter (TX) in 40-nm CMOS technology for radar and communication (RadCom) systems. To accommodate the technical requirements for RadCom systems, such as wideband operation with high linearity, a compact TX was implemented with a stacked-FET power amplifier (PA), upconverting passive mixer, and a phase-controlled push–push frequency quadrupler. The TX exhibits OP1dB and bandwidth of 13.0 dBm and 13 GHz or more, respectively, which are suitable for mid-range sensing up to 100 m with the minimum range resolution of 0.15 m or less and several tens of Gb/s short-range data transmission. In a back-to-back test, the rms error vector magnitude of −21.4 dB was achieved for 50-Gb/s 32-QAM signals occupying 13-GHz bandwidth with an output power of 4 dBm at the PA output. The total core area of the TX is 0.19 mm2.

Mixing intensification using sound-driven micromixer with sharp edges

Strong acoustic streaming can be generated inside a microchannel near sharp-edge structures. In this study, three Sharp-Edge Acoustic Streaming (SEAS) micromixers with multiple sharp edge patterns actuated by piezoelectric transducers are investigated. Direct Numerical Simulation (DNS) is used to numerically solve the multi-physics phenomenon involving acoustics, fluid dynamics and mass transfer. Experiments are carried out to validate the numerical results by visualization, as well as to evaluate micromixing performance with Iodide–Iodate Reactions. Influence of the sharp edge pattern (i.e. the spacing between individual structures, the number of sharp edges), channel throughput as well as acoustic intensity are studied. The shape of flow streamlines first unveils the interaction between acoustic streaming and main flow, which is shown to be a key for mixing enhancement. Following this, an optimal structure is found among the three mixers which allows achieving a decrease of micromixing time from 0.28 s to 0.03 s. Finally, a comparison with literature on passive mixers confirms the micromixing performance of SEAS mixer in terms of micromixing time at low Reynolds flow.