China Electronics Technology Instruments AV3672 Series, User Manual

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Appendix
Appendix 5 Amplifier Gain Compression Measurement
370
Appendix 5 Amplifier Gain Compression Measurement
This chapter introduces the basic principle and measurement method of the two-dimensional sweep option of
amplifier gain compression measurement.
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Principle of amplifier gain compression ·········································································· 370
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Overview of gain compression measurement ···································································· 370
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Steps of gain compression measurement ········································································· 375
5.1 Principle of Amplifier Gain Compression
The amplifier has a linear gain zone, in which the input power level of the amplifier is linear to the output power
level. The gain of this zone is referred to as the small signal gain (also known as the linear gain). While the input
power increases to a certain level, the gain will decrease, making the amplifier in the approximately saturated state.
The input power level at which the amplifier gain is 1dB less than the linear gain is defined as the input power of
1dB gain compression.
Fig. 5.1 Input and Output Characteristics of Amplifier
1) The amplifier gain at any power level is the slope of the corresponding curve.
2) When the amplifier works in the linear zone, the gain is constant and not related to the input power level. The
gain in this zone is often referred to as the small signal gain.
3) If the input power increases, the amplifier gain will decrease and the amplifier will work in the compression
zone.
4) The 1dB compression point is commonly used in the amplifier compression measurement. It is defined as the
input power (sometimes output power) corresponding to the 1dB decrease of the amplifier gain (equivalent to the
small signal gain of the amplifier).
If the amplifier is driven by the sine signal, the amplifier output will not be the sine signal in compression. The
output contains the harmonic component, in addition to the fundamental component of the input signal. If the input
power increases, the amplifier will be saturated, but the output power remains unchanged. In this case, the output
power does not change if the input power of the amplifier further increases. In some cases, such as the traveling
wave tube (TWT) amplifier, the actual output power will decrease if the input power continues to increase in the
saturated state. This means that the amplifier has negative gain. As the amplifier is expected to work in the linear
zone, it is important to know the input signal of gain compression.
5.2 Overview of Gain Compression Measurement
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Terms of amplifier gain compression ············································································ 413
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Terms of amplifier gain compression
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Gain compression parameters
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Compression method
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Data acquisition mode
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415
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Compression method of intelligent sweep
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417
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Factors related to measurement accuracy ········································································ 418
5.2.1 Terms of Amplifier Gain Compression