Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 70

Many of the figures of merit for power amplifiers are the same as system and LNAs, but with an emphasis on power handling. In addition, the efficiency of the amplifier is one of the key specifications that one finds primarily with power amplifiers, implying that the DC drive voltage and current must also be characterized. Because power amplifiers are often used with pulsed RF stimulus, the pulse characteristics, such as pulse profile including pulse amplitude and phase droop, are key parameters.

Power amplifiers are often driven into a non‐linear region, so the common linear S‐parameters may not apply well to predict matching. Therefore, load‐pull characterization is often performed on power amplifiers. Gain compression and output‐referred intercept point are common for power amplifiers. Some amplifier designs such as traveling‐wave‐tube amplifiers (TWT) have a characteristic that causes the output power to reach a maximum and then decrease with increasing drive power, and the point of maximum power is called saturation. Gain at rated output power is another form of a compression measurement where rather than specifying a power for which the gain is reduced by 1 dB, it specifies a fixed output power at which the gain is measured.

Power amplifiers are often specified for their distortion characteristics including IMD and harmonic content. In the case of modulated drive signals, other related figures of merit are ACPR and adjacent channel power level (ACPL). A figure of merit that combines many others is EVM, which is influenced by a combination of compression, flatness, and inter‐modulation distortion among other effects.