Experimental Control and Design of Low-Frequency Bias Networks for Dynamically Biased Amplifiers

Abstract

To reach the video bandwidth requirements on the supply paths, power amplifiers with dynamic bias schemes are constrained to reduce the values of the low-frequency (LF) decoupling capacitors on their bias lines. This can entail a decrease of the LF stability margins, among other negative effects. In this work, a methodology is proposed to experimentally monitor and control the dominant poles that govern the LF dynamics of both gate and drain bias lines from dc to high compression power. A specific topology for the bias observation accesses allows a consistent characterization in large-signal regimes. An automatic procedure to trace root contours versus four control parameters is also developed. The complete approach can be used to optimize the design of the bias lines in terms of video bandwidth, relative stability margins, and bias voltage transfer function characteristics. Moreover, the design can account for the effect of the large-signal RF drive on these LF performances. The methodology is exemplified and validated in a demonstrator prototype specifically built for that purpose.

Pole-Zero Identification: Unveiling the Critical Dynamics of Microwave Circuits Beyond Stability Analysis

“…The low-frequency dominant poles are extracted from reflection coefficient measurements performed at observation ports that are specifically included in the gate and drain bias paths of the circuit to get access to the low-frequency dynamics. This method has been used in [40] to optimize the design of the bias lines in terms of video bandwidth, relative stability margins and voltage transfer characteristics in a GaN power amplifier (Fig. 14).…”

“…Wideband [0.4-1.7 GHz] power amplifier based on GaN HEMT device CGH40010F from CREE fabricated in microstrip hybrid technology[40]. Two observation ports G and D are added in the bias paths, in series with the RC access networks.…”

“…Two observation ports G and D are added in the bias paths, in series with the RC access networks. Clouds of stable low-frequency critical poles obtained by varying three circuit parameters (gate bias, drain bias and input power) for two different values of the resistance in series with the low frequency decoupling capacitors in gate and drain[40]. (a) Series resistance of 20 .…”

A GaN HEMT Amplifier Design for Phased Array Radars and 5G New Radios

“…Radar systems, mainly 3D Active Electronically Scanned Array (AESA), strongly supported by the latest achievements in information technology, bring new challenges to the designers of transmit/receive (T/R) modules, especially High-Power Amplifiers (HPAs) based on solid-state devices [1,2]. In addition, there are currently rapid advances in high-speed wireless technology, such as 5G [3][4][5][6][7][8][9]. In particular, the power amplifiers, as a key element of RF transmitters, directly and significantly affect the operation quality of modern wireless communication systems and new generation radars [2,3,9].…”

“…Currently, such amplifiers must be linearized to meet wireless transmission standards defined e.g., by following parameters: in-band error vector magnitude (EVM), adjacent channel power ratio (ACPR), or the shape of spectrum mask [14][15][16]. There are many techniques for the amplifier linearity improvement such as e.g., analog feedforward, digital pre-distortion [6], dynamic biasing [7], envelope tracking [10], or Chireix's outphasing method [17]. However, only a few of them are suitable for linearization of amplifiers operating with wideband spectrally efficient signals and high peak-to-average power ratio (PAPR) like LTE or 5G [5,9,18].…”