Byungjoon 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

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.

High-Pass Filter Linearization Technique Using Feedforward

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.

G_{m3}

A compact UHF 3 dB power divider (PD) is presented. It consists of two identical asymmetric impedance transformers (MCCTs) and one isolation circuit with resistance and capacitance. The MCCT is composed of two different transmission-line sections and one open stub, and good frequency performance may be achieved by the combination of transmission-line sections and open stub. One PD is fabricated at a design center frequency of 500 MHz, of which total transmission-line sections are only 39.68° long. The measured bandwidth with 15 dB return loss is about 68%.

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.

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

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

As teen stress and its negative consequences are on the rise, several studies have attempted to tend to their emotional needs through conversational agents (CAs). However, these attempts have focused on increasing human-like traits of agents, thereby overlooking the possible advantage of machine inherits, such as lack of emotion or the ability to perform calculations. Therefore, this paper aims to shed light on the machine inherits of CAs to help satisfy the emotional needs of teenagers. We conducted a workshop with 20 teenagers, followed by in-depth interviews with six of the participants. We discovered that teenagers expected CAs to (1) be good listeners due to their lack of emotion, (2) keep their secrets by being separated from the human world, and (3) give them advice based on the analysis of sufficient data. Based on our findings, we offer three design guidelines to build CAs.

Compact UHF 3 dB MCCT Power Dividers

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.

A dual-band FMCW radar for through-wall detection

A digital RF receiver front-end employing a FIR(Finite Impulse Response) filter is proposed for SAW-less receiver architecture, where the large out-of-band interferer can be rejected selectively by using a scalable frequency response property of FIR filter. The FIR filter, followed by the transconductor stage and current-commutating passive mixer, operates in current domain to improve the linearity. Also, the clock generator circuit can be simplified by making the FIR filter operate with 8-phase clock signal. The designed receiver front-end is fabricated using UMC 0.13 μm CMOS process. The chip shows unwanted blocker rejection over 80 dB, with good linearity of +3.94 dB IIP3.