Seong-Kweon Kim

Fabrication of 5-GHz-band SAW filter with atomically-flat-surface AlN on sapphire

5-GHz-band surface acoustic wave (SAW) filters for mobile communications were fabricated on an atomically-flat-surface (0001)aluminum nitride/(0001)sapphire (AlN/Al/sub 2/O/sub 3/) combination. The SAW devices were fabricated using electron beam lithography and a lift-off method. Atomically-flat-surface AIN films were used to reduce SAW propagation loss. The center frequency of the fabricated SAW filter was 5.18 GHz. SAW velocity was 5688 m/s at normalized thickness by wave number (kH) of 9.9. The effective coupling coefficient was 0.1% and temperature-coefficient of delay was 9 ppm//spl deg/C at kH of 5.9. The SAW propagation loss was 0.0053 dB at 5.18 GHz. The atomically-flat-surface (0001)AlN/(0001)Al/sub 2/O/sub 3/ combination is promising for use in 5-GHz-band SAW filters for application to mobile communications.

Implementation of Orthogonal Frequency Division Multiplexing Modem Using Radix-N Pipeline Fast Fourier Transform(FFT) Processor

In this paper, a new Radix-N pipeline fast Fourier transform (FFT) processor for the implementation of IEEE 802.11a baseband orthogonal frequency division multiplexing (OFDM) modem for wireless local area network (WLAN) is proposed. The newly proposed scheme has a simple control structure and multiplication block is designed based on canonic signed digit (CSD) with N/4 twiddle factors, which enables both hardware complexity and power consumption to be reduced as about less 33% and 66% respectively than the conventional Radix-4 pipeline and Radix-2 pipeline structures. In order to verify the real time operation, the IEEE802.11a baseband OFDM test-bed with the newly proposed Radix-N pipeline FFT processor is implemented using field programmable gate array (FPGA) devices.

Highly c-axis-oriented AlN film using MOCVD for 5GHz-band FBAR filter

We have successfully developed to deposit highly c-axis-oriented aluminum nitride (AlN) film using metal-organic-chemical-vapor deposition (MOCVD). Full-width at half-maximum (FWHM) of the deposited AlN(0002) film whose thickness was 1 /spl mu/m has found to be 2.98/spl deg/. The value of FWHM means the deposited film has the electromechanical coupling coefficient (K/sup 2/) of 6.4%. The conditions of deposition were substrate temperature of 1050/spl deg/C, pressure of 20Torr, and V-III ratio of 25000. Film-bulk-acoustic resonator (FBAR) band-pass filter for 5 GHz orthogonal-frequency-division multiplexing (OFDM) wireless local area network (WLAN) system has been designed using the c-axis-oriented AlN film. The designed band-pass filter has the sufficient bandwidth of more than 100 MHz, which is evaluated from butterworth-van dyke (BVD) equivalent circuit model of FBAR.

Novel FFT LSI for Orthogonal Frequency Division Multiplexing Using Current Mode Circuit

We propose a design method of fast Fourier transform (FFT) large-scaled integration (LSI) for an orthogonal frequency division multiplexing (OFDM) system. The proposed FFT LSI is designed with simple current mode circuits, wired-OR connection and gate-width-ratioed current mirror. For a low power consumption, two design methods are proposed, current-cut (CC) and rounding process. The CC operation is performed with on-off operation of a current source. The rounding process is adopted for the component of the FFT matrix. Bit error rate (BER) in the OFDM system is simulated from 0.1 rounding step to 1.0. The BER performance of the FFT matrix with the 0.2 rounding step has little degradation from that of the original FFT matrix. The 8-point FFT LSI with the 0.2 rounding step is designed and implemented using a 0.8 µm complementary metal-oxide semiconductor (CMOS) technology. On the basis of measurement of the 8-point FFT LSI, the power consumption of the 64-point FFT LSI using CC can be estimated as being less than 10 mW.

Packet SS-CDMA modem with carrier frequency offset compensation

A new carrier frequency offset compensation algorithm for packet spread-spectrum code-division multiple-access (SS-CDMA) system is proposed. For evaluation of carrier frequency offset, 11-chip Barker codes were inserted into middle and end of the information block as pilot signals. Rotation direction and rotation amount due to carrier frequency offset are detected by phase differences between a preamble and pilot signals. Using the proposed algorithm, carrier frequency offset is evaluated by single packet. The compensation can be performed under burst transmission. We have evaluated bit error rate (BER) performance of packet SS-CDMA modem with the proposed algorithm by computer simulation. Under carrier frequency offset of less than 0.3 ppm, at the BER of 10/sup -3/, the degradation from the theoretical limit was found to be less than 0.2 dB.

New current attenuator circuit in the current mode FFT LSI for OFDM

To achieve the high performance of current-mode fast-Fourier-transform (FFT) large-scaled integration (LSI) for orthogonal frequency division multiplexing (OFDM) system, a new current-attenuator circuit without a DC offset-current error is proposed. The attainable maximum scale accuracy to the input current is theoretically -80 dB in the proposed attenuator circuit. The circuit consists of N-current mirrors simply connected in parallel with one another. The output current of the circuit is reduced to 1/N of the input current. The proposed circuit exerts high accuracy on the current attenuation and enables us to design the current-mode 64-point FFT LSI for OFDM system.

Growth of AlN film on Mo/SiO/sub 2//Si (111) for 5 GHz-band FBAR using MOCVD

We fabricated a film-bulk-acoustic resonator with high c-axis oriented AlN film on Mo/SiO/sub 2//Si (100) using metalorganic chemical vapor deposition. The resonant frequency and anti-resonant frequency of the fabricated resonator were 3.189 GHz and 3.224 GHz, respectively. The quality factor and the effective electromechanical coupling coefficient were 24.7 and 2.65%, respectively. The conditions of AlN deposition were substrate temperature of 950/spl deg/C, pressure of 20 torr, and V-III ratio of 25000. We have successfully grown high c-axis oriented AlN film with 4/spl times/10/sup -5/ /spl Omega/cm resistivity of the Mo bottom electrode. The full width at half maximum (FWHM) of the AlN (0002) on Mo/SiO/sub 2//Si (100) and Mo/SiO/sub 2//Si (111) were 4/spl deg/ and 3.8/spl deg/, respectively. The FWHM values of the deposited AlN film satisfy the RF band pass filter specification for GHz-band wireless local area network.

AlN epitaxial film on 6H-SiC(0001) using MOCVD for GHz-band SAW devices

Aluminum nitride (AlN)(0001) epitaxial films on 6H-silicon carbide (SiC)(0001) were successfully grown using metal-organic-chemical-vapor deposition (MO-CVD). Crack-free on the surface of AlN films were obtained without preannealing for removal of polishing-induced damage from the 6H-SiC(0001) substrate. The crack-free AlN films were grown at 1100/spl deg/C under V-III ratio of 25000. A SAW device was fabricated on the AlN film using photolithography and reactive ion etching (RIE) techniques. The thickness of AlN film was 1.0 /spl mu/m. The direction of SAW propagation was a-axis of AlN. The line and space of IDT was 0.6 /spl mu/m. The center frequency was measured to be 2.747GHz. The phase velocity was calculated to be nearly equal 6600m/sec. The phase velocity in AlN(0001)/6H-SiC(0001) structure is larger than that of AlN(0001)/sapphire(0001) structure under same thickness and direction of SAW propagation.

Switched-Current Analog Programmable Filter for Software-Defined Radio

We have proposed a switched-current (SI) analog programmable finite-impulse-response (FIR) filter for software-defined radio. The programmable tap coefficient circuit for programmable operation of the SI FIR filter has also been proposed. The 4-bit-resolution tap coefficient circuit has been designed and fabricated using 0.35 µm complementary-metal-oxide-semiconductor technology. The current error between measured and calculated tap coefficient circuits has been less than 2%. The radio frequency/intermediate frequency SI band-pass filter has been designed using the measured tap coefficients. The designed SI FIR filter has a frequency response as well as calculated tap coefficients. The maximum operating frequency of the proposed SI FIR filter using 0.13 µm CMOS technology has been estimated to be greater than 10 GHz with circuit simulation.

Voltage to current converter for OFDM current-mode FFT LSI

We have implemented a low power current-mode fast Fourier transform (FFT) large-scale integration (LSI) for orthogonal frequency division multiplexing (OFDM) system. In this paper, a new voltage-to-current converter (VIC) with high f?equency operation and low power consumption is proposed. From the VIC measurement result, the power consumption was 440 pW at Vdd = 1.1 V and the operating frequency amounted to 226.26 MHz.