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Gain compression
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Gain compression
Gain compression is a reduction in differential or slope gain caused by nonlinearity of the transfer function of an amplifying device for large-signal inputs.
When operating an amplifier beyond its linear range, gain compression will occur due to nonlinear circuit characteristics. The output of large amplitude inputs will be less than expected than using the small signals gain of the amplifier, such that an increase in input will not be matched by a proportional increase in output. Gain compression is the difference between the ideal linear power transfer curve and the real circuit's power transfer curve.
An important gain compression parameter is the OP1dB, which is the power input that results in a 1 dB compression of the output power (OP), corresponding to a gain ratio of 10-1⁄10 = 79.4%.
Harmonic distortion results from nonlinear transfer curves. And once an amplifier's maximum amplitude is reached, signals will be clipped, resulting in even stronger harmonic distortion.
Nonlinearity may be caused by heat due to power dissipation. Also, a transistor's operating point may move with temperature.
Gain compression is relevant in any system with a wide dynamic range, such as audio or RF. It is more common in tube circuits than transistor circuits, due to topology differences, possibly causing the differences in audio performance called "valve sound". The front-end RF amps of radio receivers are particularly susceptible to this phenomenon when overloaded by a strong unwanted signal.
A tube radio or tube amplifier will increase in volume to a point, and then as the input signal extends beyond the linear range of the device, the effective gain is reduced, altering the shape of the waveform. The effect is also present in transistor circuits. The extent of the effect depends on the topology of the amplifier.
Gain compression in RF amplifiers is similar to soft clipping. However, in narrowband systems, the effect looks more like gain compression simply because the harmonics are filtered out after amplification. Many data sheets for RF amplifiers list gain compression rather than distortion figures because it's easier to measure and is more important than distortion figures in nonlinear RF amplifiers.
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Gain compression
Gain compression is a reduction in differential or slope gain caused by nonlinearity of the transfer function of an amplifying device for large-signal inputs.
When operating an amplifier beyond its linear range, gain compression will occur due to nonlinear circuit characteristics. The output of large amplitude inputs will be less than expected than using the small signals gain of the amplifier, such that an increase in input will not be matched by a proportional increase in output. Gain compression is the difference between the ideal linear power transfer curve and the real circuit's power transfer curve.
An important gain compression parameter is the OP1dB, which is the power input that results in a 1 dB compression of the output power (OP), corresponding to a gain ratio of 10-1⁄10 = 79.4%.
Harmonic distortion results from nonlinear transfer curves. And once an amplifier's maximum amplitude is reached, signals will be clipped, resulting in even stronger harmonic distortion.
Nonlinearity may be caused by heat due to power dissipation. Also, a transistor's operating point may move with temperature.
Gain compression is relevant in any system with a wide dynamic range, such as audio or RF. It is more common in tube circuits than transistor circuits, due to topology differences, possibly causing the differences in audio performance called "valve sound". The front-end RF amps of radio receivers are particularly susceptible to this phenomenon when overloaded by a strong unwanted signal.
A tube radio or tube amplifier will increase in volume to a point, and then as the input signal extends beyond the linear range of the device, the effective gain is reduced, altering the shape of the waveform. The effect is also present in transistor circuits. The extent of the effect depends on the topology of the amplifier.
Gain compression in RF amplifiers is similar to soft clipping. However, in narrowband systems, the effect looks more like gain compression simply because the harmonics are filtered out after amplification. Many data sheets for RF amplifiers list gain compression rather than distortion figures because it's easier to measure and is more important than distortion figures in nonlinear RF amplifiers.