SiGe Power Amplifier Design and Strained-Si Device Noise Analysis
Date Issued
2006
Date
2006
Author(s)
Hua, Wei-Chun
DOI
en-US
Abstract
In this dissertation, the power amplifiers (PAs) for IEEE 802.11b/g/n wireless local area networks applications are demonstrated and the high/low frequency noise characteristics of the strained-Si nMOSFETs are studied.
A high-linearity and temperature-insensitive IEEE 802.11b/g PA with dynamic current bias is realized in a SiGe HBT technology with 0.9 µm emitter width. Due to the bias linearization, the P1dB of 27 dBm is only 0.5 dB smaller than Psat, which is the record low to the best of our knowledge. With simple temperature-insensitive bias, the total current deviations from the room temperature are smaller than 6% and 10% at the linear Pout (24/20 dBm) for IEEE 802.11b and IEEE 802.11g standards, respectively at the test temperature from 0 oC to 85 oC. The integrated power detector has a wide dynamic range of 20 dB. The dc current can be reduced to 53 mA and the power-added-efficiency (PAE) can be enhanced up to 3 times at low Pout level under dynamic current bias, and meanwhile the IEEE 802.11g linearity requirements are achieved.
A dual SiGe PAs on a single chip is then implemented based on the platform of the previous IEEE 802.11b/g PA. The large-signal and small-signal coupling effects of dual SiGe PAs for IEEE 802.11n Multiple Input Multiple Output (MIMO) applications are demonstrated for the first time. Deep trench isolation and grounded guard ring are used for crosstalk isolation at both transistor and circuit levels. The equivalent small-signal coupling at 2.45 GHz between two PAs is -30 dB. The PA delivers 18.1 dBm and 16.6 dBm with 3% EVM (OFDM, 64-QAM) in single and dual PA operation modes, respectively. The EVM degradation becomes severe as the relative interfering power level increases.
The flicker noise characteristics of strained-Si NMOSFETs are significantly dependent on the gate oxide formation. At the high temperature (900 oC) thermal oxidation, the Si interstitials at Si/oxide interface were injected into the underneath Si/SiGe heterojunction, and enhances the Ge outdiffusion into the Si/oxide interface. The Ge atoms at Si/oxide interface act as trap centers, and the strained-Si NMOSFET with thermal gate oxide yields a much larger flicker noise than the control Si device. The Ge outdiffusion is suppressed for the device with the low temperature (700 oC) tetraethylorthosilicate (TEOS) gate oxide.
The correlations between the threading dislocations and the low frequency noise characteristics of the strained-Si nMOSFETs are studied using the devices with different sizes. The device-area-dependent SVG (power spectral density of the gate referred voltage noise) ratio of the strained-Si devices over the control Si devices obtained form geometric average can be understood by the modified carrier number fluctuation model with excess traps from the Poisson distributed threading dislocations. The equivalent trap number per threading dislocation extracted from the area-dependent SVG ratios is ~85 for the strained-Si devices, and which results in about 4.2 times degradation of the SVG for the strained-Si device with the device area of 625 µm2.
The low frequency noise of the strained-Si device also shows no strained-Si layer-thickness dependence and slightly depends on the channel impurity concentration. The strained-Si layer thickness independent low frequency noise implies that we can gain the benefit of higher mobility of the thicker strained-Si layer device without sacrificing the low frequency noise performance.
The package strain improves the noise figure (NF) of the low noise amplifier (LNA). The maximum noise reduction is ~0.53 dB (13%) at the operating frequency of 2.4 GHz under the biaxial tensile strain of 0.037%. The NF reduction of the strained-LNA is mainly due to the enhanced transconductance and cut-off frequency of the individual nMOSFET device under the same strain and bias conditions.
Subjects
矽鍺
功率放大器
應變矽
閃爍雜訊
低雜訊放大器
封裝應力
SiGe
Power Amplifier
Strained Si
flicker noise
Low Noise Amplifier
Package Strain
Type
thesis
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