互调、频谱发射模板(SEM)与邻道泄露抑制比(ACLR)的深度解析
为什么需要多个线性指标？
Why multiple linearity metrics are needed?
在设备开发和测试中，特别是功放测试时，工程师们常常困惑：为什么需要互调、频谱发射模板(SEM)和邻道泄露抑制比(ACLR)等多个指标来衡量线性度？有时单载波测试ACLR满足要求，但测试SEM时却不达标。这些看似相似的线性指标为何要求不同？
In equipment development and testing, especially power amplifier testing, engineers often wonder: why do we need multiple metrics like intermodulation, Spectrum Emission Mask (SEM) and Adjacent Channel Leakage Ratio (ACLR) to measure linearity? Sometimes single-carrier ACLR tests meet requirements, but SEM tests fail. Why do these seemingly similar linearity indicators have different requirements?
指标定义对比
Definition comparison
1. 输入互调：指两个及以上载波导致的带内及带外互调干扰信号和抑制能力
1. Intermodulation: Refers to the in-band and out-of-band intermodulation interference signals and suppression capability caused by two or more carriers
2. 频谱发射模板(SEM)：设备工作频带内的载波功率带外频谱发射杂散
2. Spectrum Emission Mask (SEM): Out-of-band spectrum emission spurs of carrier power within the equipment operating frequency band
3. 邻道泄露抑制比(ACLR)：发射频率信道的平均功率与邻频率信道(或偏移量)的平均功率之比
3. Adjacent Channel Leakage Ratio (ACLR): The ratio of the average power of the transmitting frequency channel to the average power of the adjacent frequency channel (or offset)
三大核心区别
Three key differences
1. 适用范围不同：互调和ACLR针对本系统自身干扰；SEM更多考虑非本系统干扰(如LTE与NR共存)
1. Different application scopes: Intermodulation and ACLR target interference within the same system; SEM considers interference between different systems (e.g. LTE and NR coexistence)
2. 载波数要求不同：SEM仅在单载波测试；ACLR需满足单载波和多载波；互调特指多载波测试
2. Different carrier number requirements: SEM is only tested with single carrier; ACLR must meet both single and multi-carrier; Intermodulation specifically refers to multi-carrier testing
3. 指标严格度不同：以LTE为例，偏移10MHz时ACLR指标(31.98dB)比SEM转换指标(-1.98dBm/20MHz)更严格
3. Different indicator strictness: Taking LTE as an example, at 10MHz offset, ACLR indicator (31.98dB) is stricter than SEM converted indicator (-1.98dBm/20MHz)
测量带宽差异
Measurement bandwidth differences
• SEM测量带宽通常分为30KHz(PCS/卫星系统)和1MHz(WCDMA/LTE/NR)
• SEM measurement bandwidth is typically divided into 30KHz (PCS/satellite systems) and 1MHz (WCDMA/LTE/NR)
• ACLR测量带宽则根据具体通信标准而定
• ACLR measurement bandwidth depends on specific communication standards
实际应用启示
Practical implications
理解这些指标的差异有助于：
Understanding these differences helps:
1. 更精准地诊断设备性能问题
1. More accurately diagnose equipment performance issues
2. 优化功放设计时做出更全面的考量
2. Make more comprehensive considerations when optimizing power amplifier design
3. 在多系统共存场景下确保兼容性
3. Ensure compatibility in multi-system coexistence scenarios
