Showing papers by "Bumman Kim published in 2000"

Analog predistortion linearizer for high-power RF amplifiers

Abstract: We have developed an analog predistortion linearizer for a high-power amplifier of a code-division multiple-access (CDMA) base station. To effectively suppress the spectral regrowth in the adjacent channels, the odd-order intermodulation distortions (IMDs) should be cancelled. To accomplish this purpose, we employed a predistorter, which can cancel the third and fifth IMDs independently. The implemented predistorter linearized the RF amplifier with an average power of 45 dBm at 2.37-2.4-GHz band. A 9-dB suppression of spectral regrowth, from 33 to 42 dBc, was achieved for the CDMA signal with an 8.192-Mc/s chip rate over a 30-MHz bandwidth.

Analog predistortion linearizer for high power rf amplifier

Abstract: Analog predistortion linearizer for the high power amplifier of CDMA base station has been developed. To suppress the spectral regrowth in the adjacent channel effectively, the odd order intermodulation distortions should be cancelled. For the purpose, the predistorter, which can cancel the 3rd and 5th intermodulation distortions independently, has been employed. The implemented pre-distorter linearized the RF amplifier with average power 45 dBm at 2.37-2.4 GHz band. 9 dB suppression of spectral regrowth was achieved for CDMA signal over 30 MHz bandwidth.

Digital controlled adaptive feedforward amplifier for IMT-2000 band

Abstract: We present a broadband adaptive control method for IMT-2000 band multi-carrier power amplifiers adopting feedforward linearization. We have analyzed and implemented an error cancellation detection method employing a frequency hopping pilot and IF synchronous sampling correlator with DSP controller. An adaptive delta-modulated power gradient algorithm is used to adjust the signal and error cancellation loop control parameters. A 2.15 GHz feedforward power amplifier with digital controller is implemented. Band test results show that it covers over a 90 MHz band with more than 50 dBc of IMD at 5 MHz offset frequency for an 8.3 MHz WCDMA signal. The adaptation result shows very fast convergence.

Direct extraction method for internal equivalent circuit parameters of HBT small-signal hybrid-/spl pi/ model

Abstract: We present a novel and robust direct extraction method for the hybrid-/spl pi/ equivalent circuit model of a HBT. This method can accurately resolve the most important internal parameters from the measured S-parameters, and is not sensitive to the values of parasitic parameters. We derive some analytical expressions for the parameters. These analytical expressions for the hybrid-/spl pi/ equivalent circuit of the HBT ensure robust, fast, and reliable parameter extraction.

Direct extraction method for internal equivalent circuit

Abstract: We present a novel and robust direct extraction method for hybrid-n equivalent circuit model of HBT. This method can accurately resolve the most important internal parameters from the measured S-parameters, and is not sensitive to the values of parasitic parameters. We derive some analytical expressions for the parameters. These analytical expressions for hybrid-n equivalent circuit of HBT ensure robust, fast, and reliable parameter extraction.

Predistortion linearizer using even order intermodulation components

Abstract: A predistortion linearizer for predistorting a radio frequency(RF) signal includes a power divider, an even order harmonics generator and a predistortion component producer. The power divider divides the RF signal into a first and a second RF signals. The even order harmonics generator, responsive to the second RF signal, generates one or more even order harmonics of the fundamental frequencies. And, the predistortion component producer produces one or more odd order harmonics from the fundamental frequencies and the even order harmonics to provide a predistorted RF signal including the fundamental frequencies and the odd order harmonics. The power divider divides the RF signal into first and second RF signals and delays the first RF signal.

Linear amplifier using frequency 2nd order intermodulation feed-forwarding method

Abstract: A linear amplifier using a low frequency 2 nd intermodulation feed-forwarding method to offset the 3 rd intermodulation component of a fundamental signal is provided. This linear amplifier includes a transistor for amplifying the power of the fundamental signal, a first filter unit, one end of which is connected to the gate of the transistor, for filtering a 2 nd order intermodulation signal from the fundamental signal, a low frequency amplifier connected to the other end of the first filter unit, for amplifying the 2 nd order intermodulation signal with a predetermined voltage gain, and a second filter unit connected in series between the output port of the low frequency amplifier and the drain output port of the transistor, for filtering the amplified 2 nd intermodulation signal and feeding the same to the output port of the transistor. This linear amplifier feeds the low frequency 2 nd order intermodulation component of a fundamental signal forward to the output port of a power amplification transistor, thereby maintaining the stable characteristics of a circuit adopting a feed-forwarding method and favorably offsetting a 3 rd intermodulation component that is adjacent to the frequency of the fundamental signal.

The effects of nonlinear C/sub BC/ on the linearity of HBT

Abstract: It is commonly known that C/sub BC/ is a very strong nonlinear source in the HBT. To investigate the contribution of the nonlinear C/sub BC/ to the linearity, HBTs with a punch-through collector and normal collector were fabricated. At 2 GHz, the punch-through HBT and normal one exhibit the power gain of 16.6 dB and 16.9 dB, output power of 28.9 dBm and 28.6 dBm, and PAE of 51% and 59%, respectively at 1 dB gain compression point. Two-tone tests were carried out for both power devices. The normal and punch-through HBTs showed IMD3 (third-order intermodulation distortion) levels of -25 dBc and -20 dBc, respectively at 1 dB gain compression point; for both cases, IMD3 dropped to -30 dBc at 1.6 dB output power back off. Because C/sub BC/ of HBT with punch-through is linear at small input signal, the IP3 power of the HBT is higher than that of the normal HBT by 15 dB. We found that RF grounding at the collector terminal is an efficient method for third-order IM power reduction.

Measurement and Modeling of Two Tone Transfer Characteristics of High Power Amplifiers

Abstract: The high power amplifier with class AB operation has a large memory effect and high non-linearity The usual AM-AM and AM-PM data cannot properly describe the large distortion characteristics We present an accurate block model of the amplifier based on the two tone transfer characteristics The measurement setup of the two tone transfer characteristics are described The measured and modeled amplitude and phase data of the two tone harmonics versus input power level are presented This behavioral model will be very useful for the design of a predistortion linearizer of high power amplifiers and for the nonlinear system simulation with a large memory effect

Paraelectric film phase shifter

Abstract: A key component of a phased array antenna is a phase shifter. The current status of ferroelectric (and paraelectric) thin film processing enables one to expect that a tuned microwave device based on this film can be competitive with microwave ferrite and PIN diode phase shifters. An epitaxial film of BST-Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/-composition was deposited by laser ablation on an MgO substrate. With this film, a coplanar waveguide phase shifter was realized and studied. Detailed simulation of different constructions allowed the optimal design of phase shifter for MMIC to be found.

A new predistortion linearizer using low frequency even order IM components

Abstract: We present a new predistortion linearizer using low frequency even-order components. An I/Q balanced modulator is adopted as a generator of the 3rd and 5th order IM (intermodulation) components. It is very compact and could independently control the amplitudes and phases of the IM components. We have analyzed the delay mismatch effect of these predistortion circuits. The result shows that the 5th order IM components are twice as sensitive as the 3rd ones. The predistorter is implemented and tested at the IMT-2000 band. Two tone test results show that the IM3 cancellation is about 23-25 dB and the IM5 is cancelled by about 12-20 dB. The ACPR is improved by more than 11 dB for the broadband CDMA signal with a chip rate of 4.096 Mcps and this improvement is maintained through a broad range of output power level.

New Linearization Method of Mixer Using Harmonic Feed-forwarding Technique

Abstract: A new linearization method of Gilbert mixer using feed forwarding of the low frequency 2nd-order inter-modulation component is proposed. The design concept of the linearization technique is discussed and the proposed circuit methodology is applied to two single balanced mixers. The measured results show that the two circuits achieve about 10dB ACPR improvement in CDMA test and 15dB IM3 enhancement in two-tone test.

Epitaxial Ba/sub x/Sr/sub 1-x/TiO/sub 3/ thin films for microwave phase shifters

Abstract: A tunable phase shifter was fabricated with epitaxial Ba0.5Sr0.5TiO3 (BST) thin film and gold thin film in a coplanar waveguide (CPW) configuration. The BST thin film of ~0.5 μm in thickness was deposited by laser ablation on a MgO(001) single crystalline substrate. Gold electrodes of ~2 μm in thickness was prepared by thermal evaporation, followed by electroplating and wet chemical etching. Dimensional configuration of the CPW phase shifter was determined after optimizing impedance matching at 50 ohm using FEM simulation. Epitaxial quality of the BST thin film was confirmed by X-ray diffraction. Microwave performance of the phase shifter was measured at room temperature in the frequency range of 8~12 GHz, and with applied bias voltage of up to 30 V. Effect of Mn dopant in the epitaxial films was also considered.