signal processing Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as audio signal processing, sound, image processing, images, Scalar potential, potential fields, Seismic tomograph ...

, linearizers are

electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or Conductive trace, traces through which electric current can flow. It is a t ...

s which improve the

non-linear In mathematics and science, a nonlinear system (or a non-linear system) is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathe ...

behaviour of

amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power su ...

s to increase

efficiency Efficiency is the often measurable ability to avoid making mistakes or wasting materials, energy, efforts, money, and time while performing a task. In a more general sense, it is the ability to do things well, successfully, and without waste. ...

and maximum output power. Creating circuits with the inverted behaviour to the amplifier is one way to implement this concept. These circuits counteract the non-linearities of the amplifier and minimize the

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...

of the signal. This increases linear operating range up to the saturation (maximum output power) of the amplifier. Linearized amplifiers have a significantly higher efficiency with improved signal quality. There are different concepts to linearize an amplifier, including pre- and post-distortion and

feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...

linearization. Most commonly used is pre-distortion linearization. The function performed by the linearizer in relation to the amplifier is very similar to that of

eyeglasses Glasses, also known as eyeglasses (American English), spectacles (Commonwealth English), or colloquially as specs, are Visual perception, vision eyewear with clear or tinted lens (optics), lenses mounted in a frame that holds them in front ...

in relation to the eye. The eye distorts the image seen; the glasses pre-distort the image. When these two distortions are combined, the result is a clear image. For the nearsighted, the glasses must pre-distort the image one way. For the farsighted, the image must be pre-distorted in the opposite way.

Functionality of Pre-distortion Linearizers

Non-linearities occur in amplifiers due to decreasing amplification and changing phase when operated near saturation. This behavior is commonly referred to as gain or phase compression. The pre-distortion linearizer is designed to compensate these changes. The resulting behavior is commonly referred to as gain or phase expansion. A pre-distortion linearizer works by creating signal distortion (amplitude and phase) that is the complement of the signal distortion inherent in the High-Powered Amplifier. The signal to be amplified is first passed through the linearizer, distorting the signal, with no loss in gain. The distorted signal is then fed to the High-Powered Amplifier to be amplified. The distortion inherent in the High-Powered Amplifier negates the distortion introduced by the linearizer producing a near linear transfer characteristic. Gain vs Pin en2

''Figure 1'' shows the amplification (gain) contingent upon input power. The gain compression of the amplifier starts above a certain input power level (red curve). By adding a pre-distortion linearizer (blue curve) in front of the amplifier, the gain compression effect is compensated up to a certain power level (green curve). The point where the gain of the total system is starting to drop off is pushed to a higher power level thereby increasing the linear operating range. In practice, the linear output power level of an amplifier increases significantly (up to four times). Pout vs Pin

The increased linear operating range is also illustrated in ''Figure 2'' (light blue area). The chart shows the relationship between input and output power of an amplifier with and without pre-distortion linearizer. The dotted line shows the output power of the amplifier as a function of the input power on a logarithmic scale. In this illustration the compression is shown as the deviation from the ideal 45° line. The amplifier with pre-distortion linearizer (solid line) deviates from the ideal line at a much higher power level. The light blue area illustrates the improved linear operating power range gained by adding a pre-distortion linearizer.

Advantages of Pre-distortion Linearizers

Pre-distortion linearizers operate in the small signal area and increase the DC power consumption of the system only marginally. Additional advantages can be deduced including: * Small foot print, low weight. * Low cost solution compared to use of higher power amplifier in similar linear operating range. * Lower environmental impact through improved efficiency. * Retrofit possible * Adjustment to different amplifier types possible * Highly reliable

Typical Properties of a Pre-distortion Linearizer

* Dimensions: Dependent on design in the range of a few cm * Weight: 20g to 200g depending on features * Frequencies: 1 to 50 GHz with different bandwidths * Expansion levels: ** Gain: up to 10 dB, dependent on amplifier data ** Phase: up to 60°

Applications

The preferred application of linearizers is in high power amplifiers using electron tubes (traveling wave tubes, Klystron tubes, magnetron tubes) or solid state amplifiers (GaN, GaAs, Si). These systems are used in broadband voice and data transfer applications including Satellite Communication, Broadband Internet, or HD/3D television. These applications require high signal quality. The optimization of the amplifier characteristics enables the ideal use of available power and leads to energy savings of up to 50%.

References

{{Reflist

External links

* http://www.astyx.net/en/satellitenkommunikation/linearisierer.html

Electronic amplifiers An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power suppl ...

Electronic circuits