Space-Compliant Design of a Millimeter-Wave GaN-on-Si Stacked Power Amplifier Cell through Electro-Magnetic and Thermal Simulations

Abstract

The stacked power amplifier is a widely adopted solution in CMOS technology to overcome breakdown limits. Its application to compound semiconductor technology is instead rather limited especially at very high frequency, where device parasitic reactances make the design extremely challenging, and in gallium nitride technology, which already offers high breakdown voltages. Indeed, the stacked topology can also be advantageous in such scenarios as it can enhance gain and chip compactness. Moreover, the higher supply voltages and lower supply currents beneficially impact on reliability, thus making the stacked configuration an attractive solution for space applications. This paper details the design of two stacked cells, differing in their inter-stage matching strategy, conceived for space applications at Ka-band in 100 nm GaN-on-Si technology. In particular, the design challenges related to the thermal constraints posed by space reliability and to the electro-magnetic cross-talk issues that may arise at millimeter-wave frequencies are discussed. The best cell achieves at saturation, in simulation, 3 W of output power at 36 GHz with associated gain and efficiency in excess of 7 dB and 35%, respectively.

Analysis of DC negative feedback mechanism in stacked power amplifiers

“…We can see that 𝑅 𝑑𝑠 will increase with the decrease of 𝑉 𝑔𝑠 and decrease with the increase of 𝑉 𝑑𝑠 . As M1 and M2 are connected in series, we have: From (7), we can conclude that 𝑉 𝑑𝑠2 will increase because 𝑅 𝑀2 increase. So 𝑉 𝑑1 will decrease because 𝑉 𝑑2 is constant provided by the DC voltage source.…”

“…In this solution, the transistors are combined in series, resulting in a higher working voltage [3]. As a result, transistor stacking is wildly used in low-breakdown technologies, such as CMOS, GaAs and even GaN-on-Si [4,5,6,7]. Therefore, not only the AC characters but also the DC characters should be studied to make the stacked PAs work normally.…”

A Comprehensive Harmonic Analysis of Current-Mode Power Amplifiers

“…where we normalized with respect to the knee-voltage correction defined in (30) The operating power gain is defined as…”

“…Once the harmonic components of the (possibly clipped) current and voltage waveforms are known, the design rules for the PA terminations can be derived, according to the specific design target [12][13][14]. In other words, Fourier analysis [2,5] can be exploited for the theoretical analysis of any kind of PA architecture, from classical current-mode tuned-load (TL) PAs [11] to advanced architectures based on waveform engineering [15], like the harmonic tuned PA [16][17][18], the class-J PA [19,20], the class-FPA [21,22], and their variants [23][24][25][26]), on switched device operation, such as class-E [27], on series-power combination (stacked PA) [28][29][30], or finally on the load [31] and supply modulation [32] concepts.…”

A Thorough Evaluation of GaN HEMT Degradation under Realistic Power Amplifier Operation

“…The unique properties of Gallium Nitride (GaN) technology make it one of the enabling factors pushing forward the development of microwave electronics, ranging from mobile communication and radar systems to satellite communications [1][2][3][4][5][6][7]. The success of this technology lies in the physical properties of GaN [8,9], such as its high electron mobility and the wide bandgap.…”