学习日记- 2024.9.3

1. 上课情况

Analog 没怎么听，今天半天没找到AE的教学楼，到教室的时候已经没有座位了。电磁学上得太快了，自己回来学吧。

2. 复习

2.1.Wireless - lec 1

第一课的学习目标：

• Understand the basics of a: wireless link and wireless cell, the spectrum usage and
wireless signals
• Able to define and calculate the signal and noise levels in a wireless system in terms
of input/output: voltages, currents, powers, expressed in dB or dBm
• Understand the basics of antenna gain and how to use antenna gain in wireless
system calculations
• Able to calculate the link budget between a TX and RX unit
• Understand the need for low noise and high linearity in the RX path
• Understand the need for high linearity/spectral purity and efficiency in the TX path

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2.1.1 background

Wireless Cell 无线蜂窝

wireless cell is a geographical area covered by a wireless communication network, typically a single base station in cellular networks.

The cell is the area where devices can communicate with the network gh the base station. The size of the cell can vary, with smaller cells covering dense urban areas and larger cells covering rural areas.

 

Frequency band resuage 频带复用

通过在不同的地理区域内复用相同的频率，网络可以更高效地利用有限的频谱资源，从而支持更多的用户。使用小的cell ，可以节约TX功率。

 

2.1.2 basic theory

 

 

 

 

 上图是从 power gain 到 voltage gain 的推导，之前没有注意到分子是 V_out ^2 / R_out ，相应地，分母是 V_in^2 / R_in，怪不得要求 R_in = R_out，才能往后推。

noise power spectral density

The power spectral density (PSD) of thermal noise generated by a resistor Rs​ at temperature T is given by 4kTRs. (k is Boltzmann's constant)

as voltage noise 则开根号

−174dBm/Hz：the noise power spectral density when matched at the input

 

3. 预习

3.1.Wireless - lec 2 linearity

table of content

• Non-linearities in wireless systems
• Analyzing the Impact of non-linearities
  •   Taylor coefficients for Bipolar device, Bipolar diff. pair, FET device, FET diff. pair
• Harmonic distortion
• Single-tone excitation of (diff. pair) devices
• Gain compression/expansion
  •   1dB compression point
  •   Desensitization  
  •   Cross Modulation
• Intermodulation
  •   Two-tone test
  •   Intermodulation (IM3) and third-order intercept points (IP3)
  •        The linearity of cascaded non-linear stages
  •        The linearity of low-frequency feedback systems

Learning Objectives

• Understand the impact of the second and third-order non-linearities on the
performance of wireless systems
• Calculate and understand Gain compression/expansion, desensitization, and cross-
modulation in wireless systems
• Understand intermodulation and able to calculate the intermodulation for a two-tone
test in a simplified wireless system
• Able to calculate and optimize the IP3 of a wireless chain in terms of the order and
properties of its (cascaded) building blocks
• Understand the purpose and limitations of feedback to linearize a wireless system

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3.1.1 non-linearities and linearities

Linear system: In which H is the transfer (e.g., voltage gain or current gain), which should be constant in both amplitude
and phase independent of the amplitude of the input x, or the history of x. 

Nonlinear System: when its transfer depends on the amplitude of and/or history of the input x.

简而言之，看 transfer 是否是不受输入影响的定值。