Guogong Wang

Highly Efficient Monolithic Class E SiGe Power Amplifier Design at 900 and 2400 MHz

This paper discusses the impact of transistor performance and operating frequency on the design of monolithic highly efficient RF SiGe power amplifiers (PAs) using on-chip lump-element passives and/or bondwires to approximate the class E switching conditions. Single-stage SiGe PAs were designed and fabricated using both high-breakdown and high- fT devices targeting for the highest power-added-efficiency (PAE). The PAs designed using high-breakdown devices with on-chip tank inductors exhibit similar gain and PAE as those of high-fT devices, but capable of withstanding significantly higher supply voltages and deliver larger output power (> 23 dBm) more reliably. PAE of 68% (900 MHz) and 40% (2.4 GHz) was achieved from these highly integrated suboptimal PAs without using any off-chip matching. The degraded PAE at 2.4 GHz versus 900 MHz is shown to be caused by increased effective ground inductance parasitics, higher loss from both low-Q on-chip tank inductor and increased SiGe device switching loss with reduced power gain. Design insights on how to improve PAE of SiGe PAs at higher RF frequencies are discussed, as we increased the measured PAE of the class E PAs to an impressive 62-65% range at 2.3-2.4 GHz, which is among the best reported in the literature for Si-based monolithic PAs.

Ultrahigh-performance 8-GHz SiGe power HBT

A new record (FOM=3.8times105 mWmiddotGHz2 ) of power performance for SiGe power HBTs has been established in this study. By employing an extremely heavily doped base region, a record low sheet resistance of the pinch base is achieved, which offers a small base resistance and the feasibility of using wider emitter stripes. The reduction of base-collector capacitance and device size, due to the use of wider emitter stripes, dramatically improve the power gain and thus the power added efficiency

An 18-GHz 300-mW SiGe power HBT

An 18-GHz, 300-mW SiGe power heterojunction bipolar transistor (HBT) is demonstrated. The optimization of SiGe HBT vertical profile has enabled this type of devices to operate with high gain and high power at this high frequency. In the common-base configuration, a continuous wave output power of 24.73 dBm with a power gain of 4.5 dB was measured from a single 20-emitter stripe SiGe (2/spl times/30 /spl mu/m/sup 2/ of each emitter finger) double HBT. The overall performance characteristics represent the state-of-the-art SiGe power HBTs operating in the K-band frequency range.

Flexible thin-film transistors on biaxial-and uniaxial-strained Si and SiGe membranes

We report flexible thin-film transistors (TFTs) fabricated on single-crystal Si-based semiconductor membranes using Schottky source/drain contacts. Unstrained-Si, strained-Si/SiGe/Si and unstrained-Si0.8Ge0.2 alloy membranes were integrated on plastic substrates via transferring the top template layers from silicon-on-insulator (SOI) and silicon–germanium-on-insulator (SGOI) substrates. Biaxially tensile-strained Si/SiGe/Si is realized by allowing elastic strain sharing between Si and SiGe alloy. High current drive capability and high electron mobility are demonstrated on these membranes. Further enhancement of the source-to-drain current is exhibited by using mechanically introduced uniaxial strain to the flexible TFTs. We propose that the enhancement of current drive capability is attributed to both carrier mobility enhancement and Schottky barrier height modification due to strain.

Boosting up performance of power SiGe HBTs using advanced layout concept

We report an advanced power device layout structure, namely heat transfer counterbalanced (HTCB) layout, for designing power SiGe HBTs. It is shown that this new power device structure can substantially reduce adverse thermal effects of power devices without using ballasting resistors. Significantly improved power performances have been achieved from SiGe power HBTs employing the new layout concept.

Fundamental Difference of Power Handling Between CE and CB HBTs

Fundamental power handling of common-emitter (CE) and common-base (CB) (SiGe) power HBTs is compared by measuring their dynamic load lines under large-signal operation with input and output matched for maximum output power (Pout). The distinct difference of load lines indicates the fundamental different power amplification mechanisms between the two configurations. It is shown that under voltage-source bias the CE configuration always provides higher (saturated) output power (Pout) than the CB configuration, while higher power gain and power added efficiency (PAE) could be obtained from the CB configuration than the CE configuration before entering the power saturation region

Power Performance Characteristics of SiGe Power HBTs at Extreme Temperatures

This paper presents the RF (6 GHz) power performance characteristics of SiGe power HBTs at cryogenic (77K) and high operation temperature (chuck temperature 120deg C, junction temperature up to 160degC). It shows that, without specific device optimizations for cryogenic operation, the power SiGe HBTs exhibit excellent large-signal characteristics at 77K. Comparing with room-temperature operation, similar power gain, output power and PAE were obtained when the devices were operated at the cryogenic temperature. The SiGe power HBTs also operate well at high junction temperature with reasonable power gain and output power degradations. The modeling of the SiGe power HBTs under high operation temperature indicates significant increase of base resistance (RB) and emitter resistance (RE) that account for the degradation of power performance of these devices.

Configuration Dependence of SiGe HBT Linearity Characteristics

Linearity characteristics between common-emitter (CE) and common-base (CB) SiGe HBTs are compared at different frequencies, under different bias conditions and at different input/output matching conditions in this paper. It is shown that, without impedance matching at input/output of the devices, the CB configuration exhibits better linearity than the CE configuration under the same input power level and the difference of IMD3 between the two configurations decreases with the increase of operation frequency. However, when both input and output of the devices are impedance-matched for maximum output power Pout , the CE configuration has better linearity than the CB configuration. Furthermore, without varying the input/output matching, the linearity of the two configurations varies with bias in different ways that the linearity of the CE configuration degrades and that of the CB configuration improves as the bias is increased. Under certain impedance and bias conditions, the CB configuration can provide better linearity, besides higher power gain, than the CE configuration

Superiority of common-base to common-emitter heterojunction bipolar transistors

Common-emitter (CE) configuration of bipolar junction transistors has been used in virtually all amplifications since the invention of transistor, whereas common-base (CB) configuration has been rarely used due to its inferior performance in comparison to CE. For heterojunction bipolar transistors (HBTs) this conviction needs to be changed. We compared the radio-frequency (rf) power handling capability of the HBT between CE and CB configurations and analyzed their amplification mechanisms. It is found that CB HBT significantly outperforms CE HBT under proper bias conditions, revealing the significant superiority of CB to CE configuration of HBTs for rf power amplification.

Tradeoff between CE and CB SiGe HBTs for Power Amplification in Terms of Frequency-Dependent Linearity and Power-Gain Characteristics

The tradeoff between common-emitter (CE) and common-base (CB) SiGe HBTs for power amplification in terms of frequency-dependent linearity and power-gain characteristics is investigated. When both CE the CB HBTs are impedance-matched for maximum output power (Pout), the CB configuration exhibits higher power gain, however, with higher third-order intermodulation distortion (IMD3) than that of the CE configuration at high operation frequencies. At low operation frequencies, the CE configuration can exhibit the superiority on both power gain and IMD3 characteristics. New analytical expressions for IMD3 are derived and experimentally verified for the study of the frequency-dependent linearity characteristics of different configurations