good performance is good design

本文探讨了提升网站性能的关键策略与技术,包括减少连接数、避免重定向、利用HTTP流水线技术、消除渲染阻塞资源、减少客户端处理、优先加载可见内容、使用HTML5持久存储缓存、减少DOM操作、利用浏览器缓存、批处理和拆分读写操作、使用快速点击库、监听鼠标和触摸事件等方法。
zccst整理


[img]http://dl2.iteye.com/upload/attachment/0106/6581/45c9eae3-7363-3f6c-a7c6-5be0233707a2.png[/img]
[img]http://dl2.iteye.com/upload/attachment/0106/6577/1242edb0-7f9f-345a-9e85-6da5f8172b43.png[/img]


[b]good performance List:[/b]
more connections are not always a good idea. 减少连接数
[img]http://dl2.iteye.com/upload/attachment/0106/6579/006a15bc-e5c4-3433-af9f-26a6dbf5e52f.png[/img]

Avoid landing page redirects. 避开重定向
[img]http://dl2.iteye.com/upload/attachment/0106/6575/b52bf53f-d60e-3fd6-bb99-1ac60886f997.png[/img]

HTTP Pipelining(流水线技术) is most useful in high latency environment
Eliminate(除去,剔除) render blocking resources
Reduce Client-Side Processing 减少客户端处理
Prioritize visible content 优先可见的内容
Use HTML5 persistent storage for caching 使用HTML5的持久存储来做缓存
Reduce the Dom 减少DOM


避开耗资源的调用
[img]http://dl2.iteye.com/upload/attachment/0106/6573/45dea354-c70d-3418-a9e9-a27d383f5dc4.png[/img]


Leverage browser caching (利益浏览器缓存杠杆作用?)
Batch and Splitting R/W 批处理些,拆分读?
use a good fastclick library 使用一个好的快速点击库?

listen to both mouse and touch events 监听鼠标和触摸事件
Avoid unnecessary use of touch event handlers 避开不必要的触摸事件回调函数
Low-Noise Amplifiers (LNAs) are crucial components in various communication and sensing systems, as they amplify weak input signals while adding minimal noise. Here is some key information about LNA design: ### Design Goals - **Low Noise Figure**: Minimizing the noise added by the amplifier to the input signal is the primary goal. The noise figure ($NF$) is defined as the ratio of the signal-to-noise ratio (SNR) at the input to the SNR at the output, expressed in decibels ($dB$). A lower noise figure indicates better performance. - **High Gain**: LNAs should provide sufficient gain to amplify the weak input signals to a level suitable for further processing. The gain ($G$) is typically expressed in $dB$ and is defined as the ratio of the output power to the input power. - **Good Input and Output Matching**: Proper impedance matching at the input and output ports is essential to maximize power transfer and minimize reflections. This is typically achieved using matching networks. - **Wide Bandwidth**: In many applications, LNAs need to operate over a wide frequency range. Designing an LNA with a wide bandwidth while maintaining low noise and high gain can be challenging. ### Design Considerations - **Transistor Selection**: The choice of transistor is critical in LNA design. Different types of transistors, such as bipolar junction transistors (BJTs) and field-effect transistors (FETs), have different noise characteristics, gain capabilities, and operating frequencies. - **Biasing**: Proper biasing of the transistor is necessary to ensure stable operation and optimal performance. The bias point affects the transistor's gain, noise figure, and linearity. - **Matching Networks**: Matching networks are used to match the input and output impedances of the LNA to the source and load impedances, respectively. These networks can be implemented using passive components such as inductors, capacitors, and resistors. - **Feedback**: Feedback can be used to improve the stability, linearity, and noise performance of the LNA. However, it can also introduce additional noise and reduce the gain. ### Design Steps 1. **Specify the Requirements**: Determine the desired noise figure, gain, bandwidth, input and output impedances, and other performance specifications based on the application requirements. 2. **Select the Transistor**: Choose a transistor that meets the performance requirements and is suitable for the operating frequency range. 3. **Design the Biasing Circuit**: Determine the appropriate bias point for the transistor and design the biasing circuit to provide the required DC voltage and current. 4. **Design the Matching Networks**: Design the input and output matching networks to achieve the desired impedance matching and maximize power transfer. 5. **Simulate the Circuit**: Use circuit simulation software to simulate the performance of the LNA and optimize the design parameters. 6. **Fabricate and Test the Circuit**: Fabricate the LNA on a printed circuit board (PCB) or using integrated circuit (IC) technology and test its performance using appropriate measurement equipment. ### Example Design The following is a simple example of a common-source FET LNA design: ```python import numpy as np # Design parameters f = 2e9 # Operating frequency (Hz) Z0 = 50 # Source and load impedance (Ohms) NF_min = 1.0 # Minimum noise figure (dB) G_T = 15 # Transducer gain (dB) # Convert dB values to linear values NF_min_linear = 10**(NF_min / 10) G_T_linear = 10**(G_T / 10) # Calculate the required noise resistance (R_n) and optimum source reflection coefficient (Γ_s,opt) # These calculations depend on the specific transistor characteristics and are typically obtained from the datasheet # For simplicity, assume R_n = 5 Ohms and Γ_s,opt = 0.5∠45° R_n = 5 Γ_s_opt = 0.5 * np.exp(1j * np.deg2rad(45)) # Design the input matching network # Use a single-section L-match network X_s = Z0 * np.imag(Γ_s_opt) / (1 - np.abs(Γ_s_opt)**2) L_s = X_s / (2 * np.pi * f) print(f"Input inductor value: {L_s * 1e9:.2f} nH") # Design the output matching network # Assume the output impedance of the LNA is Z_out = 50 Ohms # Use a single-section L-match network X_L = Z0 * np.sqrt(G_T_linear - 1) C_L = 1 / (2 * np.pi * f * X_L) print(f"Output capacitor value: {C_L * 1e12:.2f} pF") ``` This example demonstrates the basic steps involved in designing a simple LNA using a common-source FET. However, in practice, LNA design is a complex process that requires careful consideration of many factors and may involve more advanced techniques and circuit topologies.
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