Youngoo Yang

A fully matched N-way Doherty amplifier with optimized linearity

This paper presents a new fully matched N-way Doherty amplifier. The basic principles of operation and important features are described. For the experimental verification, 2.14-GHz Doherty amplifiers having two-, three-, and four-way structures are implemented using silicon LDMOSFETs and tested using down-link WCDMA signal. The linearity performances of the two-, three-, and four-way Doherty amplifiers are optimized for better efficiency versus linearity by a bias adjustment of the peaking amplifiers. For simultaneously improving the efficiency and linearity to achieve maximum efficiency versus linearity, the gate biases of the peaking amplifiers for the N-way Doherty amplifier are optimized. As a result, the efficiency versus linearity characteristics are drastically improved by N-way extension of the Doherty amplifier.

A microwave Doherty amplifier employing envelope tracking technique for high efficiency and linearity

In this letter, we demonstrate a microwave Doherty amplifier employing an input signal envelope tracking technique. In the amplifier, the gate bias of the peaking amplifier is controlled according to the magnitude of the envelope. A 2.14-GHz Doherty amplifier is implemented using 4-W PEP LDMOSFETs, and an adaptive controlled gate bias circuit is constructed and the control shape is optimized experimentally. The performance of the microwave Doherty amplifier is compared with that of a class AB amplifier using one-tone, two-tone, and forward-link wideband code-division multiple access (WCDMA) signals. For a forward-link WCDMA signal, the measured power added efficiency (PAE) of the microwave Doherty amplifier is 39.4% at -30 dBc adjacent channel leakage ratio (ACLR), while that of the comparable class AB amplifier is 24.2% at the same ACLR level.

A highly linear and efficient differential CMOS power amplifier with harmonic control

A 2.45 GHz fully differential CMOS power amplifier (PA) with high efficiency and linearity is presented. For this work, a 0.18-/spl mu/m standard CMOS process with Cu-metal is employed and all components of the two-stage circuit except an output transformer and a few bond wires are integrated into one chip. To improve the linearity, an optimum gate bias is applied for the cancellation of the nonlinear harmonic generated by g/sub m3/ and a new harmonic termination technique at the common source node is adopted along with normal harmonic termination at the drain. The harmonic termination at the source effectively suppresses the second harmonic generated from the input and output. The amplifier delivers a 20.5dBm of P/sub 1dB/ with 17.5 dB of power gain and 37% of power-added efficiency (PAE). Linearity measurements from a two-tone test show that the power amplifier with the second harmonic termination improves the IMD3 and IMD5 over the amplifier without the harmonic termination by maximally 6 dB and 7 dB, respectively. Furthermore, the linearity improvements appear over a wide range of the power levels and the linearity is maintained under -45 dBc of IMD3 and -57dBc of IMD5 when the output power is backed off by more than 5dB from P/sub 1dB/. From the OFDM signal test, the second harmonic termination improves the error vector magnitude (EVM) by over 40% for an output power level satisfying the 4.6% EVM specification.

Analog predistortion linearizer for high power rf amplifier

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.

Effect of efficiency optimization on linearity of LINC amplifiers with CDMA signal

The linear and efficient power amplification can be achieved with LINC (linear amplification with nonlinear components) amplifiers because RF power amplifiers deal with constant envelope signals in LINC systems. To increase the average efficiency in some modulation schemes with high peak to average ratio, reactance termination in combining circuit is used. However, the shunt reactance termination degrades the linearity performance of LINC. This work shows the effect of efficiency optimization with reactance termination on ACLR (Adjacent Channel Leakage Ratio) of LINC amplifiers with WCDMA modulation systems using envelope simulation.

Experimental investigation on efficiency and linearity of microwave Doherty amplifier

We have investigated the microwave Doherty amplifier, testing for efficiency and linearity. For the experiment, a 1.4 GHz Doherty amplifier has been implemented using a silicon LDMOSFET. The Doherty amplifier-I (a combination of a class B carrier amplifier and a class C peaking amplifier) and the Doherty amplifier-II (a combination of a class AB carrier amplifier and a class C peaking amplifier) have been compared with class B and AB amplifiers, respectively, using single-tone, two-tone, and forward-link CDMA signals. It demonstrated the superior performance of Doherty amplifiers. The results provide a topology selection guide of the CDMA base station power amplifier to achieve both linearity and efficiency enhancements.

A new empirical large-signal model of Si LDMOSFETs for high-power amplifier design

We propose a new empirical large-signal model of silicon laterally diffused MOSFETs for the design of various modes of high-power amplifiers. The new channel current model has only nine parameters that represent the unique operation principles of a MOSFET. In the channel current model, we include the thermal phenomena of high-power devices. To accurately characterize high-power devices, we incorporate the channel heating and heat-sink heating effects by providing two thermal capacitances and two thermal resistances. Nonlinear capacitances, including deep subthreshold and triode regions, as well as normal saturation regions, are extracted and modeled. For validation of our model, a 1.4-GHz 5-W amplifier is implemented, and the measured and simulated results match very well.

A new linear amplifier using low-frequency second-order intermodulation component feedforwarding

A new linearization method by feedforwarding low-frequency second intermodulation component (f/sub 2/-f/sub 1/) is proposed. Drain voltage modulation by forwarding second intermodulation voltage improves linearity significantly. This new technique, which adopts a simple circuit configuration, has advantages in the stability and bandwidth due to the feedforwarding nature and shows a very good performance in comparison with other harmonic tuning circuits. Analytical derivation of low-frequency feeding voltage gain (/spl beta/) to obtain perfect cancellation of IMD/sub 3/ is presented. For verification of the proposed circuit topology, a two-tone test and a CDMA signal test at carrier frequency 2.15 GHz are performed and show about 18- and 10-dB improvement of IMD/sub 3/ and adjacent channel power ratio (ACPR), respectively.

New predistortion linearizer using low-frequency even-order intermodulation components

We present two types of new predistortion linearizers using low-frequency even-order components. One adopts an in-phase and quadrature balanced modulator as a generator of the third-order intermodulation (IM3) and fifth-order intermodulation (IM5) components and the other adopts a double-balanced diode mixer. Both types are very compact and could independently control the amplitudes and phases of the intermodulation (IM) components. We have analyzed the delay mismatch effect of these predistortion circuits. The result shows that the IM5 components are twice as sensitive than the third ones. Two types of predistorters are implemented and tested at the International Mobile Telecommunications-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 for both cases. The adjacent channel power ratio is improved by over 11 dB at the broad-band CDMA signal with a chip rate of 4.096 Mc/s, and this improvement is maintained through a broad range of output power level.

Digital controlled adaptive feedforward amplifier for IMT-2000 band

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.