Envelope-Tracking CMOS Power Amplifier Module for LTE Applications

Abstract

An envelope-tracking (ET) CMOS power amplifier (PA) is fabricated using a 0.18-m CMOS process. The module containing the supply modulator, the PA, and the output transformer is implemented on a printed circuit board (PCB). The CMOS PA employs the second and third harmonic controls at the input and the second harmonic short at the output for improved linearity. The impact on the nonlinearity of the cascode differential structure is studied and optimized. A proposed output transformer on the PCB minimizes the loss and enhances the efficiency of the PA. The ET on the gate of the common gate transistor is proposed to achieve high linearity and efficiency without using a digital pre-distortion technique. For a long-term evolution (LTE) signal at 1.85 GHz with a 10-MHz bandwidth and a 16QAM 7.5-dB peak-to-average power ratio, the ET CMOS PA module achieves a power-added efficiency of 34%, an error vector magnitude of 2.8%, and an adjacent channel leakage ratio of 34.2 dBc at an average output power of 26 dBm. The ET operation reduces the total current consumption by 10% to 34%, according to the power level, over that of the standalone PA for the LTE signal.Index Terms-CMOS, efficient, envelope tracking (ET), linear, handset, power amplifier (PA), long-term evolution (LTE).

Efficiency Enhancement Techniques for RF and MM-Wave Power Amplifiers

“…Since signal processing is a baseband operation, mainly those techniques with a strong baseband focus are successful in CMOS. For this reason, envelope modulation and restoration (EER), polar modulation and envelope tracking (ET) CMOS PAs in CMOS have seen a large success in the past few years [8,24]. Envelope Tracking (ET) has been introduced to increase the efficiency of a linear PA.…”

“…However, some successful attempts have been published already of fully integrated envelope tracking PAs. The supply modulator is typically a combination of a linear supply modulator and a switching supply modulator [24,26], which requires an additional large inductor off-chip, to achieve the high modulator efficiency. In practice, due to limited supply rejection ratio of the power amplifier, this switching modulator increases the spectral regrowth, which poses a severe threat to obey the stringent spectral purity requirements defined by the communication standards.…”

“…In practice, due to limited supply rejection ratio of the power amplifier, this switching modulator increases the spectral regrowth, which poses a severe threat to obey the stringent spectral purity requirements defined by the communication standards. In addition, substrate noise from the switching power supply modulator might affect the RF PA. To minimize the substrate noise which origins from the supply modulator in practice, both the supply modulator and the power amplifier are realized on a separate die [24,26].…”

CMOS Linear Power Amplifier with Envelope Tracking Operation (Invited Paper)

“…Proper operation of the PA should be ensured by modulation of the gate of the common gate (CG) transistor as shown in the Fig. 7, to make the common source (CS) transistor and CG transistor stay in the saturation mode [4]. The envelopeshaping ensures that the PA operates at the IMD sweet spot tracked by the envelope of the signal, and the overall IMD is improved.…”

“…Even if the SOI process overcomes the substrate loss issue with a high-resistivity insulator beneath the buried oxide, the other issues must be taken care of at the circuit level, as in the bulk CMOS process [1,2]. A cascode structure provides a solution for a low breakdown voltage [3,4]. A differential structure creates a virtual ground point and releases the source degeneration effect by a source-to-ground bonding wire [5].…”