• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.6
• /
• pp.599-604
• /
• 2002

In this paper, a digital potentiometer is used as a load resistor of a wireless optical differential detector with a polarizer, to improve the noise reduction capability. In this structure, the noise voltages of the two photodiodes are made equal by controlling a digital potentiometer and the optical noise is cancelled out. With a digital potentiometer, the signal to noise ratio is enhanced by about 23 dB.

• Journal of electromagnetic engineering and science
• /
• v.11 no.4
• /
• pp.235-238
• /
• 2011

In this paper, a novel low phase noise voltage-controlled oscillator (VCO) using metamaterial structure and rat race coupler is presented for reducing the phase noise without the reduction of the frequency tuning range. The metamaterial structure has been realized by microstrip square open loop double split ring resonator (SRR). The rat race coupler shows slightly higher transmission compared to a Wilkinson combiner and is, therefore, used instead to improve the performances of VCO. By providing these unique modifications, the proposed push-push VCO has a phase noise of -126.30~-124.83 dBc/Hz at 100 kHz in the tuning range of 5.672~5.800 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.6 s.121
• /
• pp.648-655
• /
• 2007

In this paper, we introduce a dual coil antenna which is useful for reducing the effects of radio frequency noise in an RFID system. A dual coil antenna is composed of two identical coils that are connected in series. The noise voltages in the two coils almost disappear when they are added because the magnitudes are equal and the polarities are opposite. The noise in an RFID reader with a dual coil antenna was 15 dB lower than that with a single coil antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.27 no.10
• /
• pp.945-948
• /
• 2016

Recent premium smartphones commonly employ a metal frame and this trend is currently spreading over mid-range smartphones. However, the metal frame becomes a good coupling path of electromagnetic noises emitted from digital components in smartphones and then increases radio-frequency interference(RFI) to RF antennas located at top and bottom sides of smartphones. This paper proposed a metal frame with EBG(Electromagnetic Band Gap) structure to reduce the noise coupling to antenna by suppressing surface wave on the metal frame. By simulation, it is confirmed that the proposed metal frame with $7{\times}6$ mushroom-type EBG array pattern with multi-via can reduce the noise coupling to RF antenna by about 20 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.7
• /
• pp.636-645
• /
• 2015

In this paper, unusual harmonics noise problem of digital electronic products in mass production was introduced and a practical solution was proposed. Generally, 5th or higher harmonics noise level has been ignored in circuit designs because over 5th harmonics noise decreases by 40 (dB/decade). Through some measurements, it is confirmed that over 10th harmonics noise can propagate and radiate in case of a certain PCB or housing conditions. We propose a capacitively loaded micro-strip low pass filter for commercial products having spatial design constraints and measured the effectiveness. The proposed structure can solve both of the continual increment of harmonics noise level and the spatial design constraint of commercial products. We expect the proposed method be effectively used for various digital electronic products.

• Journal of electromagnetic engineering and science
• /
• v.4 no.3
• /
• pp.137-142
• /
• 2004

In this paper, we present a new current-current negative feedback(CCNF) differential voltage-controlled oscillator (VCO) with 1/f induced low-frequency noise suppressed. By means of the CCNF, the 1/f induced low-frequency noise is removed from the proposed CCNF VCO. Also, high-frequency noise is stopped from being down-converted into phase noise by means of the increased output impedance through the CCNF and the feedback capacitor $C_f. The proposed CCNF VCO represents 11-dB reduction in phase noise at 10 kHz offset, compared with the conventional differential VCO. The phase noise of the proposed CCNF VCO is measured as - 87 dBc/Hz at 10 kHz offset frequency from 5.5-GHz carrier. The proposed CCNF VCO consumes 14.0 mA at 2.0 V supply voltage, and shows single-ended output power of - 12 dBm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.19 no.6
• /
• pp.603-611
• /
• 2008

In this paper, we introduce a multi-coil antenna which is useful for reducing the effects of radio frequency noise in an inductively coupled RFID system. A multi-coil antenna is composed of a central coil and four subsidiary coils that are connected in series. A multi-coil antenna is designed so that the total noise disappear when the induced voltages of a central coil and subsidiary coils are added. The noise in a multi-coil antenna was about 30 dB lower than that in a single coil antenna. The multi-coil antenna is very effective in noise reduction even in an environment that the spatial distribution of RF noise is changed abruptly, and the induced noise was about 16 dB lower than that in a dual coil antenna.

• Journal of electromagnetic engineering and science
• /
• v.4 no.4
• /
• pp.168-174
• /
• 2004

A bandwidth-enhanced and phase noise-improved differential LC-tank VCO is proposed in this paper. By connecting the varactors to the bases of the cross-coupled transistors of the proposed LC-tank VCO, its input negative resistance has been widened. Also, the feedback capacitor Cc in the cross-coupling path of the proposed LC-tank VCO attenuates the output common-mode level modulated by the low-frequency noise because the modulated common-mode level jitters the varactor bias point and degrades phase noise. Compared with the fabricated conventional LC-tank VCO, the proposed LC-tank VCO demonstrates $200\;\%$ enhancement in tuning range, and 6 - dB improvement in phase noise at 6 MHz offset frequency from 5.4-GHz carrier. We achieved the phase noise of - 106 dBc/Hz at 6 MHz offset, and $10\;\%$ tuning range from the proposed LC-tank VCO. The proposed LC-tank VCO consumes 12 mA at 2.5 V supply voltage.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
• /
• v.4 no.3
• /
• pp.18-29
• /
• 1993

In single mode fiber optic transmission systems(FOT's) operated at high modulation rates over long fiber spans, chromatic dispersion can produce distortion in the demodulated waveforms, resulting in intersymbol interference(ISI) in the received signal and a reduction of transmission system performance. In this paper, chromatic dispersion limitations for intensity modulation and direct detection(IM-DD) systems are studied by considering the effect of phase modulation to amplitude modulation (PM-AM) conversion noise. Laser phase noise conversion to amplitude noise due to fiber chromatic dispersion is analyzed by deriving the noise power spectral density. We first derive the noise power spectral density of the laser phase noise to intensity noise conver- sion. Next, also evaluate the system power penalty and the transmitter laser linewidth required to avoid PM-AM conversion noise penalties in long-haul nonregenerative transmission system using an external modulator and optical amplifiers. For such system with optical amplifiers, transmission sys- tem length is limited due to fiber chromatic dispersion, even if an ideal external modulator is used.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.1
• /
• pp.54-62
• /
• 1999

In this paper, we investigated the signal-to-noise ratio improvement in a differential detector, which is a function of the optical noise coupling ratio and the differential gain ratio. A differential detector consists of two photodiodes and a differential amplifier. The differential detector reduced the noise component and improved the signal-to-noise ratio by about 20 dB when the differential gain ratio equals to the optical noise coupling ratio. The differential detector is very effective in removing the environmental optical noise or interference from an adjacent optical channel. This method is also effective when the noise wavelength is similar to the signal.