Heungjae Choi | Cardiff University (original) (raw)
Papers by Heungjae Choi
ABSTRACT The photodielectric effect in antimony-doped tin oxide (Sb:SnO2) was observed by using t... more ABSTRACT The photodielectric effect in antimony-doped tin oxide (Sb:SnO2) was observed by using the microwave cavity perturbation method. The results show that the dielectric constant and the losses change upon a long 30 second exposure of 365nm irradiation. On turning off the irradiation, the dielectric constant and losses tend back towards their dark state values though never reach their starting value implying evidence of some permanently excited state within the material.
2009 European Microwave Conference, Sep 1, 2009
Design equation and synthesis of reflection type negative group delay circuit (NGDC) using transm... more Design equation and synthesis of reflection type negative group delay circuit (NGDC) using transmission line resonator (TLR) are presented. From the mathematical analysis, general equations are derived and validated with simulation for lumped element (LE) equivalent circuit. TLR-loaded reflection type NGDC is proposed to overcome the limited availability of component values required for LE structural NGDC. As a design example, single unit TLR-loaded NGDC with group delay (GD) of -8ns is designed. Simulation results agreed pretty well with the proposed design equation. To obtain broadband negative group delay with rigid flatness specification, 2-stage reflection type TLR-loaded NGDC with total group delay of -7 ns, -1.7dB loss, and 30 MHz bandwidth around 2 GHz, in which magnitude flatness of 0.1dB and group delay flatness of 0.5 ns is maintained, are fabricated and demonstrated.
Electronics Letters, Mar 12, 2009
ABSTRACT A design method for an L-band frequency quadrupler with composite right/left-handed tran... more ABSTRACT A design method for an L-band frequency quadrupler with composite right/left-handed transmission line is proposed. The left-handed transmission line in the proposed frequency quadrupler suppresses the fundamental component ( f 0), while the composite right/left-handed lambda/4 open stub reduces unwanted higher-order harmonics. From the experimental results, unwanted harmonics are suppressed to achieve harmonic distortion of 51lambdadBc minimum with output phase noise of lambda94.34lambdadBc/Hz at 10lambdakHz offset.
The 40th European Microwave Conference, Sep 1, 2010
This paper proposes a novel memory effect measurement technique in RF power amplifiers (PAs) usin... more This paper proposes a novel memory effect measurement technique in RF power amplifiers (PAs) using twotone intermodulation distortion (IMD) signal with very simple and intuitive algorithm. Based on the proposed predistortive tone cancellation technique, the proposed measurement method is capable of measuring relative phase and magnitude of the thirdorder and fifth-order IMD as well as the fundamental signal. The measured relative phase between the higher and lower IMD signal for specific tone spacing can be interpreted as the group delay information of the IMD signal concerned. From the group delay analysis, we can conclude that adaptive control of group delay as well as the magnitude and phase is a key function in increasing the linearization bandwidth and the dynamic range in the predistortion (PD) technique.
A design method to reduce the size of the planar negative group delay circuit (NGDC) is proposed ... more A design method to reduce the size of the planar negative group delay circuit (NGDC) is proposed by using a stepped impedance resonator (SIR) concept. From the conventional transmission line resonator, an equivalent stepped impedance resonator with reduced size is derived. To validate the derivation, the reflection coefficient and group delay response are compared between the two types of one-port NGDC. Finally, the reflection topology NGDC using a stepped impedance resonator is fabricated and tested. Maintaining its intrinsic electric properties, total size of the circuit is reduced to 72% from its original size.
2009 European Microwave Conference, Sep 1, 2009
A 20W class-E power amplifier (PA) with compact defected ground structure (DGS) load-network is p... more A 20W class-E power amplifier (PA) with compact defected ground structure (DGS) load-network is presented for WCDMA base-station application. From the experiments, the proposed class-E PA achieves maximum power added efficiency (PAE) of 70.2 % at the output power of 43.05 dBm with the saturation gain of 12.7 dB. Harmonics are well below -46 dBc for 2nd harmonic and -52 dBc for 3rd, 4th, and 5th harmonics through the 8 dB output dynamic range. Comparing the complexity and the size, the proposed DGS load-network is much simpler and smaller than the conventional load-network with a number of open stubs, ensuring comparable harmonic load impedance and amplifier performance.
ABSTRACT In this paper, a group delay time controller (GDTC) is proposed based on a reflection to... more ABSTRACT In this paper, a group delay time controller (GDTC) is proposed based on a reflection topology employing a parallel resonator as the reflection termination. The design equations of the proposed GDTC have been derived and validated by simulation and experimental results. The group delay time can be varied by varying the capacitance and inductance at an operating frequency. To show the validity of the proposed circuit, an experiment was performed for a wideband code division multiple access downlink band operating at 2.11 GHz to 2.17 GHz. According to the experiment, a group delay time variation of 3 +/- 0.17 ns over bandwidth of 60 MHz with excellent flatness is obtained.
2014 Ieee Mtt S International Microwave Workshop Series on Rf and Wireless Technologies For Biomedical and Healthcare Applications, Dec 1, 2014
ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor... more ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor which uses a pair of microwave split ring resonators is presented, operating around 1.4 GHz. The rings are made from silver coated copper wire. In addition to the sensing ring, a reference ring is added which operates at a higher frequency. This is used to take into account the temperature dependent expansion of the ring and to calibrate out any effects due to changes in temperature. The proposed sensor made up of the pair of rings is directly attached onto the skin in the abdominal area by using an adhesive patch. For validation, we have tested the proposed sensor simultaneously with two commercially available sensors (blood strip and continuous glucose monitor) over 12 hour periods with 3 food events, with encouraging correlation of our blood glucose results with those of the commercial sensors.
The Journal of Korean Institute of Electromagnetic Engineering and Science, 2010
IEEE Transactions on Microwave Theory and Techniques, 2015
This paper presents a method to control group delay tine using a resonance circuit. The group del... more This paper presents a method to control group delay tine using a resonance circuit. The group delay time adjuster(GDTA) that can control signal group delay time comprises a variable capacitance and a variable equivalent inductor. These are coupled in parallel at a node and also controlled by two bias voltages separately, A variable equivalent inductor is realized a transmission line terminated a variable capacitor. Group delay time can be controlled by change of capacitance and inductance, but the resonating frequency is fixed. When the proposed GDTA is fabricated on RFID Korean frequency band, a group delay variation is obtained about 3 ns.
In this work, a digital controlled co-channel feedback interference cancellation system is propos... more In this work, a digital controlled co-channel feedback interference cancellation system is proposed to reduce the feedback interference signal in the wireless repeater system. Frequency hopping spread spectrum pilot tone is adopted for the adaptive group delay detection of the feedback path. Amplitude, phase, and group delay of the feedback path are automatically detected and controlled through the comparison algorithm
IEEE Transactions on Microwave Theory and Techniques, 2015
A design of a microwave noninvasive continuous blood glucose monitoring sensor and its interferen... more A design of a microwave noninvasive continuous blood glucose monitoring sensor and its interference test results are presented. The novelty of the proposed sensor is that it comprises two spatially separated split-ring resonators, where one interacts with the change in glucose level of a sample under test while the other ring is used as a reference. The reference ring has a slightly different resonant frequency and is desensitized to the sample owing to its location, thus allowing changes in temperature to be calibrated out. From an oral glucose tolerance test with two additional commercially available sensors (blood strip and continuous glucose monitor) in parallel, we obtained encouraging performance for our sensor comparable with those of the commercial sensors. The effects of endogenous interferents common to all subjects, i.e., common sugars, vitamins (ascorbic acid), and metabolites (uric acid) have also been investigated by using a large Franz cell assembly. From the interference test, it is shown that the change in sensor response is dominated by changes in glucose level for concentrations relevant to blood, and the effects of interferents are negligible in comparison.
2014 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications (IMWS-Bio2014), 2014
ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor... more ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor which uses a pair of microwave split ring resonators is presented, operating around 1.4 GHz. The rings are made from silver coated copper wire. In addition to the sensing ring, a reference ring is added which operates at a higher frequency. This is used to take into account the temperature dependent expansion of the ring and to calibrate out any effects due to changes in temperature. The proposed sensor made up of the pair of rings is directly attached onto the skin in the abdominal area by using an adhesive patch. For validation, we have tested the proposed sensor simultaneously with two commercially available sensors (blood strip and continuous glucose monitor) over 12 hour periods with 3 food events, with encouraging correlation of our blood glucose results with those of the commercial sensors.
2011 IEEE MTT-S International Microwave Symposium, 2011
ABSTRACT In this paper, we propose a novel composite negative group delay circuit to reduce the s... more ABSTRACT In this paper, we propose a novel composite negative group delay circuit to reduce the signal attenuation required to obtain negative group delay. It is already known that negative group delay can be obtained in a specific frequency of signal attenuation. For the same negative group delay of -6 ns, the signal attenuation of the conventional circuit is 31.25 dB, while the proposed composite circuit involves signal attenuation of only 13.9 dB. As a result, the number of gain compensating amplifiers can be reduced. This contributes to the efficiency enhancement as well as out-of-band noise reduction and stable operation when integrated into the power amplifier linearization system.
2008 International SoC Design Conference, 2008
This paper presents a novel high-Q inductor using conventional grounded active inductor and feedb... more This paper presents a novel high-Q inductor using conventional grounded active inductor and feedback parallel resonance circuit. The proposed high-Q inductor using tunable LC resonance circuit (HITR) consists of the conventional active grounded inductor and feedback parallel resonance circuit which is composed of low-Q spiral inductor and MOS varactor. The novelty of the proposed structure is based on the increase of Q-factor by feeding parallel resonance circuit into gyrator structure. The high-Q inductor is fabricated by 0.18um Hynix CMOS technology. The fabricated inductor shows inductance of above 45 nH and Q-factor of over 640 around 5.4 GHz.
2007 Asia-Pacific Microwave Conference, 2007
In this paper, the design of a novel dual-band feedforward linear power amplifier (FFW LPA) is pr... more In this paper, the design of a novel dual-band feedforward linear power amplifier (FFW LPA) is presented. The frequencies of operation of the implemented dual-band FFW LPA are the digital cellular (f0=880MHz) band, and the IMT-2000 (f0=2.14GHz) band, which are separated about 1.26GHz. Using high power amplifiers (120W PEP) for commercial basestation application, the IMD cancellation loop shows 20.45dB and 25.04dB suppression for the cellular and IMT-2000 bands, respectively, over a correction bandwidth of 100MHz. From the adjacent channel leakage ratio (ACLR) measurement with CDMA IS-95A 4FA and WCDMA 4FA signal, we obtained 16.5dB improvement at the average output power of 41.5 dBm for digital cellular band, and 18.6dB improvement at the average output power of 40dBm for IMT-2000 band under simultaneous operation.
ABSTRACT The photodielectric effect in antimony-doped tin oxide (Sb:SnO2) was observed by using t... more ABSTRACT The photodielectric effect in antimony-doped tin oxide (Sb:SnO2) was observed by using the microwave cavity perturbation method. The results show that the dielectric constant and the losses change upon a long 30 second exposure of 365nm irradiation. On turning off the irradiation, the dielectric constant and losses tend back towards their dark state values though never reach their starting value implying evidence of some permanently excited state within the material.
2009 European Microwave Conference, Sep 1, 2009
Design equation and synthesis of reflection type negative group delay circuit (NGDC) using transm... more Design equation and synthesis of reflection type negative group delay circuit (NGDC) using transmission line resonator (TLR) are presented. From the mathematical analysis, general equations are derived and validated with simulation for lumped element (LE) equivalent circuit. TLR-loaded reflection type NGDC is proposed to overcome the limited availability of component values required for LE structural NGDC. As a design example, single unit TLR-loaded NGDC with group delay (GD) of -8ns is designed. Simulation results agreed pretty well with the proposed design equation. To obtain broadband negative group delay with rigid flatness specification, 2-stage reflection type TLR-loaded NGDC with total group delay of -7 ns, -1.7dB loss, and 30 MHz bandwidth around 2 GHz, in which magnitude flatness of 0.1dB and group delay flatness of 0.5 ns is maintained, are fabricated and demonstrated.
Electronics Letters, Mar 12, 2009
ABSTRACT A design method for an L-band frequency quadrupler with composite right/left-handed tran... more ABSTRACT A design method for an L-band frequency quadrupler with composite right/left-handed transmission line is proposed. The left-handed transmission line in the proposed frequency quadrupler suppresses the fundamental component ( f 0), while the composite right/left-handed lambda/4 open stub reduces unwanted higher-order harmonics. From the experimental results, unwanted harmonics are suppressed to achieve harmonic distortion of 51lambdadBc minimum with output phase noise of lambda94.34lambdadBc/Hz at 10lambdakHz offset.
The 40th European Microwave Conference, Sep 1, 2010
This paper proposes a novel memory effect measurement technique in RF power amplifiers (PAs) usin... more This paper proposes a novel memory effect measurement technique in RF power amplifiers (PAs) using twotone intermodulation distortion (IMD) signal with very simple and intuitive algorithm. Based on the proposed predistortive tone cancellation technique, the proposed measurement method is capable of measuring relative phase and magnitude of the thirdorder and fifth-order IMD as well as the fundamental signal. The measured relative phase between the higher and lower IMD signal for specific tone spacing can be interpreted as the group delay information of the IMD signal concerned. From the group delay analysis, we can conclude that adaptive control of group delay as well as the magnitude and phase is a key function in increasing the linearization bandwidth and the dynamic range in the predistortion (PD) technique.
A design method to reduce the size of the planar negative group delay circuit (NGDC) is proposed ... more A design method to reduce the size of the planar negative group delay circuit (NGDC) is proposed by using a stepped impedance resonator (SIR) concept. From the conventional transmission line resonator, an equivalent stepped impedance resonator with reduced size is derived. To validate the derivation, the reflection coefficient and group delay response are compared between the two types of one-port NGDC. Finally, the reflection topology NGDC using a stepped impedance resonator is fabricated and tested. Maintaining its intrinsic electric properties, total size of the circuit is reduced to 72% from its original size.
2009 European Microwave Conference, Sep 1, 2009
A 20W class-E power amplifier (PA) with compact defected ground structure (DGS) load-network is p... more A 20W class-E power amplifier (PA) with compact defected ground structure (DGS) load-network is presented for WCDMA base-station application. From the experiments, the proposed class-E PA achieves maximum power added efficiency (PAE) of 70.2 % at the output power of 43.05 dBm with the saturation gain of 12.7 dB. Harmonics are well below -46 dBc for 2nd harmonic and -52 dBc for 3rd, 4th, and 5th harmonics through the 8 dB output dynamic range. Comparing the complexity and the size, the proposed DGS load-network is much simpler and smaller than the conventional load-network with a number of open stubs, ensuring comparable harmonic load impedance and amplifier performance.
ABSTRACT In this paper, a group delay time controller (GDTC) is proposed based on a reflection to... more ABSTRACT In this paper, a group delay time controller (GDTC) is proposed based on a reflection topology employing a parallel resonator as the reflection termination. The design equations of the proposed GDTC have been derived and validated by simulation and experimental results. The group delay time can be varied by varying the capacitance and inductance at an operating frequency. To show the validity of the proposed circuit, an experiment was performed for a wideband code division multiple access downlink band operating at 2.11 GHz to 2.17 GHz. According to the experiment, a group delay time variation of 3 +/- 0.17 ns over bandwidth of 60 MHz with excellent flatness is obtained.
2014 Ieee Mtt S International Microwave Workshop Series on Rf and Wireless Technologies For Biomedical and Healthcare Applications, Dec 1, 2014
ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor... more ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor which uses a pair of microwave split ring resonators is presented, operating around 1.4 GHz. The rings are made from silver coated copper wire. In addition to the sensing ring, a reference ring is added which operates at a higher frequency. This is used to take into account the temperature dependent expansion of the ring and to calibrate out any effects due to changes in temperature. The proposed sensor made up of the pair of rings is directly attached onto the skin in the abdominal area by using an adhesive patch. For validation, we have tested the proposed sensor simultaneously with two commercially available sensors (blood strip and continuous glucose monitor) over 12 hour periods with 3 food events, with encouraging correlation of our blood glucose results with those of the commercial sensors.
The Journal of Korean Institute of Electromagnetic Engineering and Science, 2010
IEEE Transactions on Microwave Theory and Techniques, 2015
This paper presents a method to control group delay tine using a resonance circuit. The group del... more This paper presents a method to control group delay tine using a resonance circuit. The group delay time adjuster(GDTA) that can control signal group delay time comprises a variable capacitance and a variable equivalent inductor. These are coupled in parallel at a node and also controlled by two bias voltages separately, A variable equivalent inductor is realized a transmission line terminated a variable capacitor. Group delay time can be controlled by change of capacitance and inductance, but the resonating frequency is fixed. When the proposed GDTA is fabricated on RFID Korean frequency band, a group delay variation is obtained about 3 ns.
In this work, a digital controlled co-channel feedback interference cancellation system is propos... more In this work, a digital controlled co-channel feedback interference cancellation system is proposed to reduce the feedback interference signal in the wireless repeater system. Frequency hopping spread spectrum pilot tone is adopted for the adaptive group delay detection of the feedback path. Amplitude, phase, and group delay of the feedback path are automatically detected and controlled through the comparison algorithm
IEEE Transactions on Microwave Theory and Techniques, 2015
A design of a microwave noninvasive continuous blood glucose monitoring sensor and its interferen... more A design of a microwave noninvasive continuous blood glucose monitoring sensor and its interference test results are presented. The novelty of the proposed sensor is that it comprises two spatially separated split-ring resonators, where one interacts with the change in glucose level of a sample under test while the other ring is used as a reference. The reference ring has a slightly different resonant frequency and is desensitized to the sample owing to its location, thus allowing changes in temperature to be calibrated out. From an oral glucose tolerance test with two additional commercially available sensors (blood strip and continuous glucose monitor) in parallel, we obtained encouraging performance for our sensor comparable with those of the commercial sensors. The effects of endogenous interferents common to all subjects, i.e., common sugars, vitamins (ascorbic acid), and metabolites (uric acid) have also been investigated by using a large Franz cell assembly. From the interference test, it is shown that the change in sensor response is dominated by changes in glucose level for concentrations relevant to blood, and the effects of interferents are negligible in comparison.
2014 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications (IMWS-Bio2014), 2014
ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor... more ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor which uses a pair of microwave split ring resonators is presented, operating around 1.4 GHz. The rings are made from silver coated copper wire. In addition to the sensing ring, a reference ring is added which operates at a higher frequency. This is used to take into account the temperature dependent expansion of the ring and to calibrate out any effects due to changes in temperature. The proposed sensor made up of the pair of rings is directly attached onto the skin in the abdominal area by using an adhesive patch. For validation, we have tested the proposed sensor simultaneously with two commercially available sensors (blood strip and continuous glucose monitor) over 12 hour periods with 3 food events, with encouraging correlation of our blood glucose results with those of the commercial sensors.
2011 IEEE MTT-S International Microwave Symposium, 2011
ABSTRACT In this paper, we propose a novel composite negative group delay circuit to reduce the s... more ABSTRACT In this paper, we propose a novel composite negative group delay circuit to reduce the signal attenuation required to obtain negative group delay. It is already known that negative group delay can be obtained in a specific frequency of signal attenuation. For the same negative group delay of -6 ns, the signal attenuation of the conventional circuit is 31.25 dB, while the proposed composite circuit involves signal attenuation of only 13.9 dB. As a result, the number of gain compensating amplifiers can be reduced. This contributes to the efficiency enhancement as well as out-of-band noise reduction and stable operation when integrated into the power amplifier linearization system.
2008 International SoC Design Conference, 2008
This paper presents a novel high-Q inductor using conventional grounded active inductor and feedb... more This paper presents a novel high-Q inductor using conventional grounded active inductor and feedback parallel resonance circuit. The proposed high-Q inductor using tunable LC resonance circuit (HITR) consists of the conventional active grounded inductor and feedback parallel resonance circuit which is composed of low-Q spiral inductor and MOS varactor. The novelty of the proposed structure is based on the increase of Q-factor by feeding parallel resonance circuit into gyrator structure. The high-Q inductor is fabricated by 0.18um Hynix CMOS technology. The fabricated inductor shows inductance of above 45 nH and Q-factor of over 640 around 5.4 GHz.
2007 Asia-Pacific Microwave Conference, 2007
In this paper, the design of a novel dual-band feedforward linear power amplifier (FFW LPA) is pr... more In this paper, the design of a novel dual-band feedforward linear power amplifier (FFW LPA) is presented. The frequencies of operation of the implemented dual-band FFW LPA are the digital cellular (f0=880MHz) band, and the IMT-2000 (f0=2.14GHz) band, which are separated about 1.26GHz. Using high power amplifiers (120W PEP) for commercial basestation application, the IMD cancellation loop shows 20.45dB and 25.04dB suppression for the cellular and IMT-2000 bands, respectively, over a correction bandwidth of 100MHz. From the adjacent channel leakage ratio (ACLR) measurement with CDMA IS-95A 4FA and WCDMA 4FA signal, we obtained 16.5dB improvement at the average output power of 41.5 dBm for digital cellular band, and 18.6dB improvement at the average output power of 40dBm for IMT-2000 band under simultaneous operation.