Now showing 1 - 10 of 78
  • Publication
    Simplified online coefficients updating for digital predistortion of wideband/multi-band RF power amplifiers
    (IEEE, 2015-12-09) ; ;
    In this paper, a simplified online coefficients updating technique is proposed to realize real-time timing of digital predistortion (DPD) for RF power amplifiers (PAs), particularly focusing on wideband and concurrent multi-band scenarios. It is achieved by equally weighting the memory terms in conventional DPD models that leads to a significant reduction of numerical calculation complexity in the coefficients updating process and thus saves time and power during real system operation. To validate the proposed method, both wideband LTE- A (100 MHz) and concurrent dual-band (20 MHz + 20 MHz) cases have been tested. Experimental results show that the proposed method can achieve excellent performance with significant reduction of system complexity compared to the conventional approaches.
      291Scopus© Citations 2
  • Publication
    A Broadband High-Efficiency Doherty Power Amplifier with Integrated Compensating Reactance
    This paper presents a high-efficiency gallium nitride Doherty power amplifier (DPA) using an integrated compensating reactance (CR) for broadband operation. With an additional quarter-wavelength transmission line integrated in the peaking amplifier output, a CR is generated to compensate the load impedance of the carrier amplifier in the low-power region and thus enhance the back-off efficiency over a wide frequency range without affecting the Doherty load modulation at saturation. For this purpose, a peaking output matching network (OMN) is employed to convert the output impedance of the peaking device into quasi-short circuit when it is off and achieve proper impedance matching when it is on. A two-point matching technique using the transmission (ABCD) matrix is employed to design such desired OMN. Measurement results show that the DPA has a 6-dB back-off efficiency of 50%-55% and a saturated efficiency of 57%-71% over the frequency band of 1.7-2.8 GHz (49% fractional bandwidth). When driven by a 20-MHz long term evolution modulated signal at 6.5-dB back-off power, the DPA can achieve an average efficiency of more than 50% with high linearity after linearization over the design frequency band.
      585Scopus© Citations 98
  • Publication
    A channelized sideband distortion model for suppressing unwanted emission of Q-band millimeter wave transmitters
    In this paper, a channelized sideband distortion model is proposed to suppress the unwanted emission of Q-band millimeter wave (mmWave) transmitters in wideband contiguous carrier aggregation scenarios. By employing this model, the compensating bandwidth or center frequency can be agilely controlled. Experiments were conducted on a 40 GHz mmWave power amplifier to validate this idea. The satisfactory performance proved that the proposed model is a promising candidate for future 5G applications.
      154Scopus© Citations 6
  • Publication
    Broadband Fully Integrated GaN Power Amplifier With Embedded Minimum Inductor Bandpass Filter and AM-PM Compensation
    In this paper, we present a design technique for broadband linearized fully integrated GaN power amplifiers (PAs). The minimum inductor bandpass filter structure is used as the output matching network to achieve low loss and high out-of-band attenuation. Two parallel transistors with unbalanced gate biases are used to mitigate nonlinearity of their transconductance and input capacitance, and consequently, compensate AM-PM distortion of the PA. A fully integrated GaN PA prototype provides 35.1–38.9 dBm output power and 40-55% power-added efficiency (PAE) in 2.0–4.0 GHz. For a 64-QAM signal with 8-dB peak-to-average power ratio (PAPR) and 100-MHz bandwidth at 2.4 GHz, average output power of 32.7 dBm and average PAE of 31% are measured with −30.2 dB error vector magnitude (EVM).
  • Publication
    Decomposed Vector Rotation-Based Behavioral Modeling for Digital Predistortion of RF Power Amplifiers
    (IEEE, 2015-01-14)
    A new behavioral model for digital predistortion of radio frequency (RF) power amplifiers (PAs) is proposed in this paper. It is derived from a modified form of the canonical piecewise-linear (CPWL) functions using a decomposed vector rotation (DVR) technique. In this model, the nonlinear basis function is constructed from piecewise vector decomposition, which is completely different from that used in the conventional Volterra series. Theoretical analysis has shown that this model is much more flexible in modeling RF PAs with non-Volterra-like behavior, and experimental results confirmed that the new model can produce excellent performance with a relatively small number of coefficients when compared to conventional models.
      514Scopus© Citations 113
  • Publication
    A Fully Integrated GaN Dual-Channel Power Amplifier With Crosstalk Suppression for 5G Massive MIMO Transmitters
    We present a broadband dual-channel power amplifier (PA) with crosstalk suppression for multi-input multi-output (MIMO) communications. Operation of MIMO system with crosstalk is theoretically evaluated for two popular coding schemes including the space-time coding and linear precoding. Design challenges of a multi-channel PA on a single chip are investigated and circuit techniques, including second-harmonic trapping integrated into the output matching network and the use of back-via lines to isolate the channels, are proposed to mitigate the inter-channel crosstalk. A fully integrated dual-channel PA prototype, implemented using a 250-nm GaN-on-SiC process, provides 34.9–36.3 dBm output power, 44–49% power-added efficiency (PAE), 11.3–12.3 dB power gain, 31.0–34.2 dB second-harmonic rejection, and –28.1 dB to –25.7 dB inter-channel crosstalk across 4.5–6.5 GHz. For a 100-MHz 256-QAM signal with 7.2 dB peak-to-average power ratio (PAPR), the PA achieves 29.9 dBm average output power, 30% average PAE–, 38.2/–39.1 dBc adjacent channel leakage ratio (ACLR), and –28.2 dB (3.9%) rms error vector magnitude (EVM), without using digital predistortion (DPD). Effect of crosstalk on linearity of the dual-channel PA is also measured and it is shown that for a 256-QAM signal EVM can increase by 3–8 dB, depending on relative power levels of the two channels.
      211Scopus© Citations 11
  • Publication
    Digital Suppression of Transmitter Leakage in FDD RF Transceivers With an Enhanced Low-Sampling Rate Behavioral Model
    With continuously increasing of signal bandwidth, the transmitter leakage issue in frequency division duplexer (FDD) transceivers becomes severer. In this letter, an enhanced behavioral model is proposed to suppress FDD transmitter leakage at a low-sampling rate. The theoretical analysis is provided to explain the operation principle of the proposed model. The experimental results show that the proposed model can effectively increase the accuracy of generating sideband replica and thus improve the suppression performance.
      301Scopus© Citations 4
  • Publication
    Low-Cost FPGA Implementation of Volterra Series-Based Digital Predistorter for RF Power Amplifiers
    (IEEE, 2010-04) ;
    This paper presents a low-complexity and low-cost hardware implementation of a Volterra series-based digital predistorter (DPD). This is achieved by introducing two novel model complexity reduction techniques into the system, namely, lookup table assisted gain indexing and time-division multiplexing for multiplier sharing. Experimental results show that this novel DPD implementation uses much less hardware resources, but still maintains excellent performance compared to conventional approaches.
      420Scopus© Citations 77
  • Publication
    Pattern Sensing Based Digital Predistortion of RF Power Amplifiers under Dynamical Signal Transmission
    In this paper, a pattern sensing based digital predistortion (DPD) technique for radio frequency (RF) power amplifiers (PAs) under dynamical signal transmission is proposed. Unlike conventional methods where real time re-calibration is required, this approach utilizes a low resolution amplitude-modulation to amplitude-modulation (AM/AM) pattern to sense PA characteristics and then quickly select proper DPD coefficients to linearize the PA. Experimental results show that the proposed method can provide an efficient a nd effective w ay to deal with complex dynamic signal transmission scenarios and maintain very good linearization performance, which is very suitable for future 5G applications.
      119Scopus© Citations 2
  • Publication
    Adaptive semiblind background calibration of timing mismatches in a two-channel time-interleaved analog-to-digital converter
    This paper introduces an adaptive semiblind background calibration of timing mismatches in a two-channel time-interleaved analog-to-digital converter (TIADC). By injecting a test tone at the frequency of half the overall sampling frequency of TIADC, the timing mismatch between two sub-ADCs can be quickly estimated with great accuracy without affecting the normal operation of the TIADC. The estimated coefficient can then be used in compensation module formed by a fixed structure to calibrate the timing mismatches. Simulation results demonstrate the effectiveness of the proposed estimation and correction technique.
      121Scopus© Citations 12