• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.5
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• pp.1349-1359
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• 1998

In this paper, presented is the result of a digital implementation of a FM stereo composite signal generator. The chip utilizing DDFS(Direct Digital Frequency Synthesizer architecture is implemented using $1.0\mu\textrm{m}$ CMOS gate-array technology thereby replacing analog componentry. To verify the process of generating composite signals a conventional logic simulation method was used. The processed chip was mounted on an evaluation PCB to test and analyze to signals. According to the measurement result obtained by using a 12-bit DAC, the digital FM composite signal generator produces a 74DB spectrally pure signal over its entire tuning range, which is superior to that of analog counterpart by 14dB in it spectral reponse. And further enhancements of the spectral response is expected to be achieved by using a high resolution digital to analog converter, such as a 16-bit DAC. The resulting signals is superior to the signal of the analoy circuitry typically used, in major characteristics such as S/N ratios, accuracy, tuning stability, and signal seperation.

• The Journal of the Acoustical Society of Korea
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• v.18 no.5
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• pp.52-57
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• 1999

It is very important to design of QAM modulator of high spectral efficiency for high speed data transmission. In this paper, typical 16-QAM modulator is designed by modification design of DDFS(direct digital frequency synthesizer). DDFS generates sinusoidal waveform digitally to the frequency setting word. Phase modulation is accuratly made by control of a generated phase increment value and amplitude modulation is accomplished in the D/A converter output by control of amplitude level. For the suppression of harmonics and glitch, dual-structured DDFS is studied to improve the spurious characteristics. P-Spice is used for design and simulation in mixed mode. Also we can get the satisfactory results of designed 16-QAM modulator from the constellation output.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.12
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• pp.1251-1257
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• 2014

In this paper, a 6~13 GHz ultra high speed frequency synthesizer having minimum 30 kHz step size and minimum 500 ns frequency settling time is proposed. In order to obtain fast settling time, fine resolution, and good phase noise performance, wideband output frequencies were synthesized based on DDS(Direct Digital Synthesizer) and analog direct frequency synthesis technology. The phase noise performance of wideband frequency synthesizer was estimated by the superposition theory and its results were compared with measured ones. The measured frequency settling time was below 500 ns, phase noise was below -106 dBc @ 10 kHz at 13 GHz, and frequency accuracy was measured below ${\pm}2kHz$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.333-341
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• 2015

In this paper, a 0.5~4 GHz frequency synthesizer having good phase noise performance is proposed. Wideband output frequencies of the synthesizer were synthesized using DDS(Direct Digital Synthesizer) and analog direct frequency synthesis technology in order to obtain fast settling time. Also in order to get good phase noise performance, 2.4 GHz DDS clock was generated by VCO(Voltage Controlled Oscillator) which was locked by the 100 MHz reference oscillator using SPD(Sample Phase Detector). The phase noise performance of wideband frequency synthesizer was estimated and the results were compared with the measured ones. The measured phase noise of the frequency synthesizer was less then -121 dBc @ 100 kHz at 4 GHz.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.1
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• pp.73-79
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• 2020

Modern radar system requires high spectral purity and low phase noise characteristics for very low RCS target detection and high resolution SAR (Synthetic Aperture Radar) image. This paper presents a new X-band high stable frequency synthesizer for high performance radar system, which combines DAS (Direct Analog Synthesizer) and DDS (Direct Digital Synthesizer) techniques, in order to cope with very low phase noise and high frequency agility requirements. This synthesizer offers more than 10% operating bandwidth in X-band frequency and fast agile time lower than 1 usec. Also, the phase noise at 10kHz offset is lower than -136dBc/Hz, which shows an improvement of more than 10dB compared to the current state of art frequency synthesizer. This architecture can be applied to L-band and C-band application as well. This frequency synthesizer is able to used in modern AESA (Active Electronically Scanned Array) radar system and high resolution SAR application.