A Quadrature Digital Power Amplifier With Hybrid Doherty and Impedance Boosting for Complex Domain Power Back-Off Efficiency Enhancement

Abstract

A quadrature digital power amplifier (PA) with hybrid Doherty and impedance boosting (HDIB) technique is presented for deep power back-off (PBO) efficiency enhancement in the complex domain. Less power-combining ways and dc power supplies are required for proposed PA comparing to previously reported works with deep PBO efficiency enhancement. A reconfigurable matching network (RMN) based on a novel reconfigurable transformer is proposed with more freedom to achieve a flexible load impedance tuning range of the sub-PAs. The characteristics of the reconfigurable transformer based on tunable inductors are analyzed. Efficiency enhancement is achieved at 3-/6-/9-/12-/15-dB PBOs without any supply switching or PA short-switches. The PA is fabricated in 40-nm CMOS technology with a core size of 0.83 mm 2 . Operating at 2.3-3.4 GHz, it introduces 24.2-dBm peak P out with 38.5% peak drain efficiency (DE) at 2.8 GHz. It achieves 38.5%/29.6%/18.4% at 2.8 GHz and 34.7%/26.6%/17.8% DE at 3.3 GHz for 0-/6-/12-dB PBO, 39.3%/29.5%/14.9% at 2.8 GHz, and 35.3%/27.9%/15.9% DE at 3.3 GHz for 3-/9-/15-dB PBO, respectively. For 10-MHz 256-QAM modulation signal, it delivers 16.22-/15.50-dBm average P out with EVM of −32.3/−33.0 dB, average DE of 24.6%/22.7%, and ACLR of −33.20/−31.54 dBc at 2.8/3.3 GHz, respectively. For 20-MHz 64 QAM modulation signal, it exhibits 16.42-/15.52-dBm average P out with EVM of −29.1/−29.3 dB, average DE of 24.9%/22.78%, and ACLR of −30.78/−30.74 dBc at 2.8/3.3 GHz, respectively.

Quadrature Switched/Floated Capacitor Power Amplifier With Reconfigurable Self-Coupling Canceling Transformer for Deep Back-Off Efficiency Enhancement

“…The extra inductor L t and tunable capacitor C t are introduced in the transformer. The equivalent secondary inductance L se is determined by C t and L t EM coupled to L s with coupling coefficient k st [25]. Meanwhile, the equivalent primary inductance L pe is also affected by L t and C t due to the unwanted coupling between L t and L p with coupling factor k pt .…”

“…To increase the efficiency of PA at PBOs, various techniques are developed, such as envelop tracking (ET) [1], [2], outphasing [3]- [7], Doherty [8]- [13], load modulation [14], [15], and Class-G [16], [17]. To further improve the PA efficiency at deep PBO, the multi-way combined Doherty PA with switched transformer [18], Class-G Doherty [19]- [21], subharmonic switching (SHS) [22]- [24], and hybrid Doherty with impedance boosting [25] are developed. The multi-way combined PA with switched transformer introduces various efficiency peaks due to the load modulation [18], which suffers from relatively large circuit size and limited passive efficiency.…”

“…The SHS PAs [22]- [24] can enhance the PA efficiency at deep PBO by using subharmonic component of carrier frequency, which sacrifices the circuit size due to multiple power combined ways. The technique of hybrid Doherty and impedance boosting [25] increases the PA efficiency at deep PBO with less power-combining ways and dc power supplies. However, the degraded passive efficiency limits the PA efficiency at deep PBO.…”

“…Meanwhile, the technique of I/Q cell sharing can increase the peak efficiency of quadrature TX [31]. Recently, the quadrature PAs with PBO efficiency enhancement are reported with competitive performances [25], [30]- [35]. However, it is still challenging to increase the efficiency at deep PBOs for quadrature PAs.…”

A mm-Wave Switched-Capacitor RFDAC

“…In addition, RFDACs 1 typically offer improved energy efficiency when compared to analog PAs. At sub-6-GHz frequencies, RFDAC structures have been recently improved with many innovations that focus on increasing the back-off efficiency using switched transformers [12]- [14] or sub-harmonic LO techniques [15], [16]. A key challenge with RFDACs is that they have mostly been limited in operational frequency due to the limited ability for a transistor to switch at higher frequencies.…”