Kye-Ik Jeon

A predistortion linearizer using envelope-feedback technique with simplified carrier cancellation scheme for class-A and class-AB power amplifiers

A predistortion linearization method using an envelope-feedback technique is proposed and implemented in this paper. This linearizer compensates the gain and phase nonlinearity of power amplifier (PA) simultaneously by controlling both variable attenuator and phase shifter with the feedback of only the difference signal between input and output envelopes. A new carrier cancellation scheme composed of a minimization circuit, log detector, and vector modulator is also presented. This circuit achieves adaptive control of the linearizer by enabling direct measurement of out-of-band power. It is well suited to a multichannel system where the allocated channels are time variant. The principle of the proposed linearizer is described and simple AM-AM distortion analysis is presented analytically and graphically based on the conceptual schematic diagram. A two-tone test for a class-A PA at 1.855 GHz with frequency spacing of 1 MHz showed intermodulation-distortion reduction of maximum 16 dB and stable operation over 5-dB output power variation up to 4-dB backoff from the saturation power level. The proposed linearizer is also applicable to class-AB PAs without further special adjustments. The adaptation circuit is fully implemented with analog integrated circuits, which can further extend its applicability with the integration technology.

A New GaAs Field Effect Transistor (FET) with DIpole Barrier (DIB)

A new GaAs field effect transistor (FET) with dipole-barrier (DIBFET) employing a delta-n (δn) layer and a delta-p (δp) layer is proposed and fabricated. Electrons are confined in the upper undoped-GaAs layer (the channel layer) rather than around the δn layer by the influence of the transverse electric field resulting from the dipole-barrier formation. This leads to the high electron concentration of 1.5×1018 cm-3 with the electron drift mobility of 3600 cm2/Vs in the undoped GaAs channel at room temperature. The fabricated GaAs DIBFET with 0.8 µm gate length shows the maximum value of extrinsic transconductance of 366 mS/mm. The drain current density is larger than 800 mA/mm. The current gain cutoff frequency f T of 16.7 GHz and the maximum oscillation frequency f max of 67 GHz are obtained. One-dimensional calculation of device characteristics is performed for the purpose of evaluating the device performance.

Highly Linear Predistortion Power Amplifiers With Phase-Controlled Error Generator

A simple predistortion technique to cancel the fifth-order intermodulation (IM5) as well as third-order intermodulation (IM3) components using a third-order predistorter (PD) is represented. The IM3 and IM5 components are cancelled out simultaneously by their same magnitude and phase difference in the PD and power amplifier (PA). Moreover, this phase difference is controlled by using the phase-controlled error generator in the PD. For experimental verification, a third-order PD has been implemented and tested in a 30-W class-AB PA at the wide-band code division multiple access (WCDMA) band of 2.11-2.17GHz. Two-tone test results show that significant cancellation of the IM3 and IM5 components can be obtained. For a four-carrier WCDMA application, significant adjacent channel leakage ratio improvement is achieved over a wide range of output power levels

A frequency dispersion model of GaAs MESFET for large-signal applications

Deficiencies in conventional frequency dispersion models of GaAs MESFET are addressed regarding their large-signal response. A new model which can accurately describes the large-signal dynamic properties is proposed. Only DC and scattering parameter data are required to extract the model parameters, which can be easily implemented into microwave circuit simulators in the macro circuit form. The validity of this model is demonstrated by comparing predicted pulsed I-V characteristics and power saturation characteristics with measured ones.

Input harmonics control using non-linear capacitor in GaAs FET power amplifier

We address the effect of gate signal distortion arising from capacitance non-linearity on the power added efficiencies of power amplifiers based on FETs. A novel method which can compensate the non-linearity of gate capacitance is proposed. The key idea is that a reversed diode is connected to the gate, where the gate and source part of a FET is simply modeled as a diode. We demonstrated this scheme with the load-pull and source-pull measurement of the circuit. A 7% increase in power added efficiency is achieved.

The IMD sweet spots varied with gate bias voltages and input powers in RF LDMOS power amplifiers

In this paper, the intermodulation distortion (IMD) sweet spots that are varied with gate bias voltage and input power in RF power amplifiers are predicted with simple mathematical analysis. The analysis is based on the ID-VGS transfer characteristic curve and odd-order two-tone distortion products. The mathematically derived IMD sweet spots have similar behavior with those of measurement applied to 940 MHz LDMOS RF power amplifiers. The approach can be used in predicting optimum gate bias voltage to minimize the 3rd-order intermodulation (IM3).

A new predistortion linearizer using envelope-feedback technique for PCS high power amplifier application

A predistortion linearizing method using an envelope-feedback technique is proposed and implemented. This linearizer compensates the gain and phase nonlinearity of the power amplifier at the same time by controlling both variable attenuator and phase shifter with the feedback of only the difference signal between the input and output envelopes. Also a new way to achieve signal cancellation is presented with the combination of a minimization circuit, log detector and vector modulator. A two-tone test for a class-A power amplifier at 1.855 GHz with a frequency spacing of 1 MHz showed an IMD reduction of 16 dB maximum and stable operation over 5 dB output power variation up to 4 dB back-off. The proposed linearizer is also applicable to class-AB and class-B power amplifiers without any special adjustments. The adaptation algorithm is fully implemented with analog ICs, which can further extend its applicability with the integration technology.

Design and fabrication of 77 GHz HEMT mixer modules for automotive applications using experimentally optimized antipodal finline transitions

77 GHz PHEMT gate mixer module and resistive mixer module were fabricated for automotive applications using the LG-CIT low noise PHEMT process and WR12-to-microstrip antipodal finline transitions. The finline transitions were experimentally optimised for wideband operation and low insertion loss by adjusting the geometrical design parameters. The average insertion loss was measured to be 0.74 dB per transition in the 75-90 GHz range. The fabricated gate mixer module and the resistive mixer module showed very good conversion loss of 2 dB and of 10.3 dB, respectively, including finline transition loss and IF cable loss, which were very competitive performances.

A 2.14 GHz class-E LDMOS power amplifier

This paper describes a high efficiency class-E power amplifier using the experimental- based design method. The class-E power amplifier is designed and implemented using an LDMOSFET with a 10 W peak envelope power (PEP) at a band of 2.14 GHz. To suppress harmonic powers and reduce losses, the output matching network using transmission lines is used. From measured results, the drain efficiency of 65.2 % with a power gain of 13.8 dB is achieved at a Pout of 39.84 dBm. Also, the 2nd - and 3rd - harmonic power levels are reduced below -48 dBc.

Linearity improvement of RF power amplifiers using a simple high-order predistorter for WCDMA applications

A simple high-order predistorter to cancel the 3rd - and 5th -order intermodulation (IM3 and IM5) components of RF power amplifiers is proposed. The IM3 and IM5 components are cancelled out simultaneously by using their identical magnitude and phase difference in the predistorter and power amplifier. For experimental verification, a high-order predistorter has been implemented and tested with a 45-W class-AB power amplifier at wide-band code division multiple access (WCDMA) band of 2.11-2.17 GHz. The measured results show the significant cancellation of IM3 and IM5 components for a two-tone test and the notably improved adjacent channel leakage ratio (ACLR) for four-carrier WCDMA applications over a wide range of output power levels.