Duksoo Kim

A Transconductor and Tunable

A linearization technique of a transconductor circuit is proposed in this brief. By adopting a two-path feedforward architecture, the Gm3 component of the transconductor vanishes and a highly linear V-to-I conversion is achieved. This technique consists of self-biased inverters only, and it can be applied to transconductors with differential inputs. It also has an advantage in process scaling and precise bias control is not necessary. A tunable Gm-C high-pass filter for the baseband of a frequency- modulated continuous-wave radar system is implemented using these linearized transconductors. The filter is synthesized with a high-order admittance method. The designed filter is fabricated in a 0.13-μm CMOS process. The filter cutoff frequency can be tuned from 0.15 to 0.75 MHz with a current consumption value of 11-36 mA. An in-band input-referred third-order intercept point of +19.4 dBm and a 1-dB compression point of +5.35 dBm are measured, demonstrating a highly linear filter operation.

G_{m}-C

The Ru valence at the Mn sites in Pr0.5Sr0.5MnO3 has been studied using thermoelectric power (TEP) and Ru K- and LIII-edge X-ray absorption near edge structure (XANES) spectroscopy. In comparison with TEP value at 400 K for Pr1−xSrxMnO3 and Pr0.5Sr0.5Mn1−xRuxO3, it was found that the Mn-site doped Ru is in the mixed valence state between 4+ and 5+. Ru K- and LIII-edge XANES study of Pr0.5Sr0.5Mn1−xRuxO3 (x = 0.04 and 0.1) also confirmed the mixed valence state of Ru from the fact that XANES spectrum of the Mn-site doped Ru is in between those of tetravalent and pentavalent ruthenates. These results indicate that the change of carrier density with Ru doping is not sufficient to understand the drastic enhancement of ferromagnetism observed in Ru-doped Pr0.5Sr0.5MnO3. The prime role of Ru is discussed in terms of Mn valence change and magnetic interactions between Mn and doped Ru ions.

High-Pass Filter Linearization Technique Using Feedforward

A dual-band through-the-wall imaging radar receiver for a frequency-modulated continuous-wave radar system was designed and fabricated. The operating frequency bands of the receiver are S-band (2–4 GHz) and X-band (8–12 GHz). If the target is behind a wall, wall-reflected waves are rejected by a reconfigurable G m –C high-pass filter. The filter is designed using a high-order admittance synthesis method, and consists of transconductor circuits and capacitors. The cutoff frequency of the filter can be tuned by changing the reference current. The receiver system is fabricated on a printed circuit board using commercial devices. Measurements show 44.3 dB gain and 3.7 dB noise figure for the S-band input, and 58 dB gain and 3.02 dB noise figure for the X-band input. The cutoff frequency of the filter can be tuned from 0.7 MHz to 2.4 MHz.

G_{m3}

This paper presents a dual band CMOS power amplifier (PA) for an S/X band high resolution radar system. Reconfigurable band-switchable matching networks and a dual band Wilkinson power combiner (impedance transformer) are used for an output matching network. The PA is fabricated using a UMC 0.13 μm CMOS process. It provides a saturated output power of 24.8 dBm and 25.3 dBm with the power-added-efficiency (PAE) of 27.2 % and 36.4 % at 8.4 GHz and 3.0 GHz, respectively. The 3-dB bandwidth is 2.5 GHz (7.4-9.9 GHz) and 2.3 GHz (2.7-5.0 GHz). This amplifier achieves a fractional bandwidth of 29% and 60 % at each band, and shows suitable performance for use in a high resolution radar system.

Canceling

In this paper, a dual-band, frequency-modulated continuous-wave (FMCW) radar for short-range through-wall detection is proposed and implemented. This radar adopts a shared-aperture antenna technique for reducing antenna area and high-speed chirping to avoid flicker noise. It operates at the S-band (3 GHz) and the X-band (9 GHz), with 486 MHz chirp bandwidth and 860 MHz chirp bandwidth, respectively. The chirp rates are 11,050 GHz/s and 22,000 GHz/s at the S- and X-bands, respectively. The radar has successfully detected a target through a wooden wall.

Valence state of Ru at the Mn sites in Pr0.5Sr0.5MnO3: Thermoelectric power and X-ray absorption near-edge structure spectroscopy

Abstract The electrical transport properties of La-chalcogenides (La 2.989 S 4 , La 2.985 Se 4 , Ce 3 S 4 ) are investigated by measuring the magnetoresistance and thermoelectric power (TEP). The superconducting La 2.989 S 4 with T c =8.2 K shows a clear phase transition at around T ∼90 K, which is consistent with the structural phase transition temperature. La 2.985 Se 4 is also superconducting with T c =5.7 K. In the case of Ce 3 S 4 , the ferromagnetic transition is observed at T m =7.2 K and there is no superconducting or structural phase transition. The temperature dependence of TEP of the above three La-chalcogenides shows metallic characteristics with magnitudes of −10 μ V/K at room temperature. The broad peak at low temperature in TEP of Ce 3 S 4 is discussed with the role of the f-electron in Ce 3 S 4 comparing with superconducting La 2.989 S 4 and La 2.985 Se 4 .

A Dual-Band Through-the-Wall Imaging Radar Receiver Using a Reconfigurable High-Pass Filter

The temperature-dependent resistivity of Sr1 − xKxBiO3, with x = 0.4–0.6, has been measured as a function of the magnetic field (or electrical current). Although X-ray diffraction results are more or less identical to single phase for the measured 10 samples, the EDS results indicate that the potassium content, x, varies from 0.4 to 0.6 and the electrical resistance varies quite sensitively from sample to sample. For the samples of resistivity less than 4 mΩ cm at room temperature with ρ(15 K)/ρ(273 K) < 0.9, superconductivity is observed with Tc ∼ 12 K. Other samples exhibit a reentrant resistance below the superconducting transition temperature. The reentrant resistance, however, decreases as the external magnetic field (or electrical current) is applied, and some samples show the recovery of superconductivity upon the application of a magnetic field (or electrical current). Disorderness in the junction area between superconducting grains seems to be vital for the observed anomalous reentrant resistance. Further investigations are on to understand this intriguing phenomena.

A dual band CMOS power amplifier for an S/X band high resolution radar system

This paper presents a high gain and high harmonic rejection low-noise amplifier (LNA) for software-defined radio receiver. This LNA exploits the high quality factor (Q) series resonance technique. High Q series resonance can amplify the in-band signal voltage and attenuate the out-band signals. This is achieved by a source impedance transformation. This technique does not consume power and can easily support multiband operation. The chip is fabricated in a 0.13-μm CMOS. It supports four bands (640, 710, 830, and 1,070 MHz). The measured forward gain (S21) is between 12.1 and 17.4 dB and the noise figure is between 2.7 and 3.3 dB. The IIP3 measures between 5.7 and 10.8 dBm, and the third harmonic rejection ratios are more than 30 dB. The LNA consumes 9.6 mW from a 1.2-V supply.

A dual-band FMCW radar for through-wall detection

In this paper, we propose a wideband receiver that can achieve wideband input matching characteristic and remove out-of-band blocker signals. A wideband input matching is achieved by adding a feedback path to a basic wideband receiver structure consisting of low-noise transconductance amplifier (LNTA), passive mixer, and baseband transimpedance amplifier (TIA). We also proposed a method of cancelling the blocker signal by adding an auxiliary downconversion path. This method can minimize the additional circuit by using the transparent characteristics of the passive mixer and can eliminate the blocker signal without causing the performance degradation of the receiver to be large. A wideband receiver circuit designed with 65nm process was simulated. The receiver can cover the frequency range from 50 MHz to 1.95 GHz and has 47.9 dB gain and 4.1 dB noise figure performance. It also achieves an additional 9.8 dB of blocker signal cancellation over the basic wideband receiver.

Magnetoresistance and thermoelectric power of La-chalcogenides (La2.989S4, La2.985Se4, Ce3S4)

This letter proposes a novel frequency-modulated continuous-wave radar to achieve high wall-clutter rejection with a low-order high-pass filter (HPF). The proposed radar has two phase-locked loops (PLLs) and a phase controller. One transmitter PLL generates a chirp signal for transmitting (TX chirp) signal, the other a local-oscillator (LO) PLL generates a chirp signal for mixing (LO chirp), and the phase controller controls a phase of a reference clock entering the transmitter PLL. When the phase controller advances by a half-period of the reference clock, the PLL tracks and locks onto the advanced reference clock, and the TX chirp signal is advanced by a half-period of the reference clock. If longer advanced time is needed, the above-mentioned process (advance, track, and lock) is repeated after PLL locking. In this manner, long advanced time can be achieved with a fine time-resolution. The use of appropriate advanced time decreases the time gap between a wall-reflection signal and the LO chirp signal, and increases the ratio of target beat-frequency to wall beat-frequency. This enables a low-order HPF to fully attenuate wall-clutter. Moreover, this technique decouples the relationship between the wall’s distance and the HPF’s cut-off frequency. The radar was implemented and measured. The wall was located at 1.5 m and the target was located at 3 m. The measured results show that a second-order HPF attenuates by more than 20 dB for the wall beat-frequency signal, while it does not attenuate the target beat-frequency signal.