Reconfigurable Low-pass Filter Research Articles

A Closed-Loop Reconfigurable Analog Baseband Circuitry With Open-Loop Tunable Notch Filters to Improve Receiver Tx Leakage and Close-in Blocker Tolerance

This paper presents an analog baseband (ABB) circuit in a 0.13 μm SiGe technology for transmitter leakage cancellation and close-in blocker suppressions in fully duplex (FD) frequency-modulated continuous-wave (FMCW) radar. This ABB comprises a programmable gain amplifier (PGA) and a cascaded LPF/Notch hybrid, which incorporates a closed-loop (CL) reconfigurable low-pass filter (LPF) and an open-loop (OL) tunable notch filter. The adopted key topologies include active-RC bi-quads and Gm-C ones. In an FD FMCW transceiver, Tx leakage and close-in blockers are difficult to be eliminated in the RF domain, especially when leakage/blockers are very close to desired signals or even in-band in the frequency domain. This LPF/notch hybrid is proposed to solve this issue. The LPF and PGA provide bandwidth (BW)/gain programmability, while the Gm-C bi-quad provides adaptable center frequency for a notch filter. With this adaption, the notch filter could be adjusted to match the leakage/blocker offset frequency. Thus, digitally discrete programmability and analog continuous tuning capability are combined in this solution for improving the overall front-end interference robustness without de-sensitizing the Rx. Furthermore, the order of LPF/notch hybrid is programmable from 2 to 10 with a step of 2 for different rejection levels of interferences. The measured chip achieves a -3dB bandwidth of 6 21 MHz with 4-bit digital control and 1 MHz/step programmability, and a voltage gain of 0 70 dB with 9-bit digital control (3-bit from pre-amplifier, and 6-bit from PGA with 1 dB/step). With the condition of 15 dB gain, output P-1dB is 11.8 dBm@3MHz, and the output IP3 is 20.8 dBm@3MHz.

A 10.23–15.7-GHz Varactor-Tuned Microstrip Bandpass Filter With Highly Flexible Reconfigurability

This article demonstrates a 10.23–15.7-GHz varactor-tuned microstrip bandpass filter (BPF) with fully controllable center frequency, bandwidth, and transmission zeros. The concept of cascading a tunable low-pass unit together with a tunable high-pass unit is adopted to achieve the reconfigurable BPF. A comprehensive loss analysis is carried out to determine the preferable circuit topologies for low-pass filter (LPF) and high-pass filter (HPF), respectively. This not only overcomes the limitation of low quality factor of varactor at high frequency, but also contributes to a highly flexible reconfigurability of the BPF. A reconfigurable LPF using defected ground structure (DGS) and a quasi-elliptic HPF using microstrip technology are then proposed to demonstrate the improved BPF performance at high frequency. The measured results show that the designed BPF is capable of operating in five working modes, with a center frequency tuning range from 10.23 to 15.7 GHz and a fractional bandwidth (FBW) tuning range from 32.48% to 95.76%. The minimum in-band insertion loss reaches 2.55 dB. A steep cutoff characteristic and ultrawide stopband with high rejection level are successfully achieved and are well preserved during the whole tuning process, demonstrating the superiority of the designed BPF.

Reconfigurable Low-Pass Filter With Sharp Roll-Off and Wide Tuning Range

A miniaturized reconfigurable low-pass filter (LPF) with a sharp roll-off, wide tuning range, and extended stopband is presented in this letter. The proposed LPF consists of two fixed low-pass (LP) cells and a tunable bandstop (BS) cell loaded with two pairs of varactor diodes. The BS cell with tunable stopband edges is employed to achieve the reconfigurable cutoff frequency and sharp roll-off characteristics in the whole LPF. The fixed LP cells are utilized to suppress the high passband of the BS cell, which obtain the tunable LP filtering response and wide stopband. For experimental demonstration purposes, a microstrip prototype of the proposed reconfigurable LPF with a wide fractional tuning range of 78.8% and roll-off rate over 103 dB/GHz is simulated, fabricated, and measured. The wide stopband is extended up to 10 GHz with a rejection level better than 15 dB, and the overall dimension is $0.078\lambda _{\mathrm {g}} \times 0.08\lambda _{\mathrm {g}}$ . This physical size is comparable to more compact, prior art reconfigurable LPFs while featuring among the sharpest roll-off rate ever reported.

Photonic compressive sensing for analog-to-information conversion with a delay-line based microwave photonic filter

Compressive sensing (CS) in the photonic domain is highly promising for analog-to-information conversion of sparse signals due to its potential capability of high input bandwidth and digitization with sub-Nyquist sampling. In this paper, we suggest that the concept of delay-line based microwave photonic filter be used in photonic CS to realize the low-pass filtering (LPF) function which is required in CS. A microwave photonic filter (MPF) with a dispersive element and fiber delay lines is applied in photonic CS to achieve better performance and flexibility. In the approach, the input radio-frequency signal and the pseudorandom bit sequence (PRBS) are modulated on a multi-wavelength optical carrier and propagate through a dispersive element. The modulated optical signal is split into multiple channels with tunable delay lines. The multiple wavelengths, dispersive element and multiple channels constitute a reconfigurable low-pass microwave filter. Experiment and simulations are presented to demonstrate the feasibility and potentials of this approach.

Tunable low-pass MEMS filter using defected ground structures (DGS)

A tunable bandstop filter applying the micromachined technology is designed, simulated and fabricated. The filter is realized by incorporating defected ground structures structures with the micromachined switches. The surface micromachining fabrication process is employed on the high resistivity silicon substrate to fabricate the filter. The measured 3-dB cut-off frequency changes of the reconfigurable low-pass filter for four different states has been analyzed. The measured insertion loss is very lower in four tuning range of the filter. This work demonstrates the possibility of high-performance compact-size reconfigurable filters at mm-waves using multiple-contact micromachined switches. Simulated and measured results of the proposed filter show good agreements. The entire reconfigurable filter was realized in a small chip size of 1.2mm×1.5mm.

Design of an Active-Gm-RC Reconfigurable Filter for the Multi-Mode Receiver

Based on TSMC 0.18m RF CMOS process a reconfigurable low-pass filter (LPF) is presented in this paper. The LPF adopts active-Gm-RC structure. By manually adjusting the capacitor arrays, the LPF can switch working mode and correct frequency offset caused by process deviation. The pre-layout simulation shows that with 1.8V power supply, the bandwidth ranges from 1.4MHz to 9.8MHz with a step of 1.4MHz. The out of band attenuation is about-80dB/10 octave and the power consumption is 0.43mW .

Two-state reconfigurable miniaturized low-pass filter using micromachined double-contact RF switches

This paper presents a compact micromachined two-state reconfigurable low-pass filter (LPF). Frequency tunability of the proposed LPF could be efficiently and precisely achieved by ON/OFF actuations of two types of single-crystal silicon (SCS) double-contact RF MEMS switches. The use of the SCS double-contact switches as frequency-tuning elements on the reconfigurable filter has two main advantages: the number of the tuning elements required can be reduced by half, and mechanical robustness and reliable filter operations can be provided owing to the deform-free properties and stable actuating behavior of the SCS actuators. The proposed filters and switches were monolithically fabricated using a robust silicon-on-glass (SiOG) process. A frequency tuning ratio of 2.5:1 was successfully obtained and the average insertion losses on the passbands were changed only by 0.05 dB between the two reconfigured filter states.

Miniature and tunable millimeter-wave lowpass filter with MEMS switch

In this paper, fully monolithic tunable millimeter-wave filters with tapped-line feedings are proposed using the CPW-based periodic structures with novel multiple-contact MEMS switches. Millimeter-wave low-pass filters were designed, fabricated, and tested. The cascaded CPW-based periodic structures, with low-pass intrinsic filtering characteristics, are reconfigured into a self-similar single unit cell by the operation of the novel multiple-contact MEMS switches with single actuation. The measured results of the reconfigurable low-pass filter show the 3-dB cutoff frequency change from 19 to 11 GHz with very small change in the average insertion loss from 1.3 to 1.9 dB. The chip size of the low-pass is 4.0 mm × 1.6 mm.

LOW POWER LOW-PASS FILTER WITH PROGRAMMABLE CUTOFF FREQUENCY BASED ON A TUNABLE UNITY GAIN FREQUENCY OPERATIONAL AMPLIFIER

In this paper, a sixth-order reconfigurable low pass filter (LPF) is realized using 0.25 μm TSMC CMOS technology. The filter is based on a cascading connection of bi-quadratic active-Gm-RC cells. The active-Gm-RC cells are realized using compensated op-amps with variable transconductance gain and variable compensation capacitors (variable Gm–Cc op-amp). The tuning range of the filter's cutoff frequency is from 77.4 KHz to 37.78 MHz. The filter operates from a single supply of 1.5 V. Simulations results using PSPICE for the proposed reconfigurable LPF are presented.

Millimeter-wave MEMS tunable low pass filter with reconfigurable series inductors and capacitive shunt switches

In this paper, a new type of reconfigurable inductor is proposed for mm-waves based on the reconfiguration of slow-wave coplanar waveguide (CPW) lines using multiple-contact switches. It is then employed together with micro-electro-mechanical systems (MEMS) capacitive shunt switches to realize a reconfigurable low-pass filter, where the values of both inductors and capacitors are changed independently to achieve optimum filter characteristics. The measured 3-dB cut-off frequency of the reconfigurable low-pass filter changes from 53 GHz to 20 GHz while maintaining Tchebycheff low-pass prototype characteristics. The out-of-band rejection characteristics are also improved in this way. To our knowledge, this is among the first demonstrations that both types of MEMS contact switches and capacitive switches are used simultaneously to construct a monolithic tunable filter with independent L/C controlling capability.

Reconfigurable millimeter-wave filters using CPW-based periodic structures with novel multiple-contact MEMS switches

In this paper, fully monolithic reconfigurable millimeter-wave filters are proposed using the CPW-based periodic structures with novel multiple-contact MEMS switches. Millimeter-wave low-pass and band-pass filters were designed, fabricated, and tested. Three cascaded CPW-based periodic structures, with low-pass and band-pass intrinsic filtering characteristics, are reconfigured into a self-similar single unit cell by the operation of the novel multiple-contact MEMS switches with single actuation. By using the multiple-contact MEMS switches, the insertion loss can be reduced and the operating frequency ranges are extended to millimeter-waves with little increase of loss. Additionally, the number of the switching elements has been reduced and the bias-decoupling circuits are not required, resulting in a very small chip size. The measured results of the reconfigurable low-pass filter show the 3-dB cutoff frequency change from 67 to 28 GHz with very small change in the insertion loss from 0.32 to 0.27 dB. The center frequency of the reconfigurable band-pass filter is tuned from 55 to 20 GHz, and the measured 3-dB cutoff bandwidth changed from 32 to 12 GHz, while the average insertion loss changed from 1.27 to 1.61 dB. The chip size of the low-pass and band-pass filter including dc bias line is 1.2 mm /spl times/ 1.5 mm and 1.2 mm /spl times/ 4.5 mm, respectively.

A compact low-loss reconfigurable monolithic low-pass filter using multiple-contact MEMS switches

A high-performance reconfigurable low-pass filter based on the quasifractal self-similar structures has been developed at millimeter-waves using multiple-contact MEMS switches. Three-cell cascaded low-pass structure was reconfigured to one-cell low-pass counterpart by activating the micromachined switches to achieve 3:1 frequency scaling. Two types of special multiple-contact MEMS switches were developed to reduce the number of switching elements as well as to reduce the insertion loss and, thus, extend the operating frequencies to mm-waves. In addition, bias-decoupling circuits were eliminated, resulting in a small chip size of 1.2 mm /spl times/ 1.5 mm. The measured 3-dB cut-off frequency of the reconfigurable low-pass filter changed from 67 GHz to 28 GHz with minor change in the insertion loss from 0.32 dB to 0.27 dB. This work demonstrates the possibility of high-performance compact-size reconfigurable filters at mm-waves using multiple-contact micromachined switches.