If the PA is to operate entirely in its linear region, then taking into account the very high peak to average ratio of the cable signals (typically 14 dB) means that the amplifiers need to operate on average 14 dB below the start of compression, hence ensuring that no signal compression occurs even at the peaks of the signal.
The maximum instantaneous peak efficiency can be calculated to be 50% (when the signal envelope is at maximum, assuming inductive loading). The power amplifiers are very low efficiency Class A architectures. Although the system consumes nearly 80 W of power, just 2.8 W of signal power is delivered. Power efficiencies in cable power amp drivers.įigure 1 provides an overview of a typical cable application. The trade-off for this mode of operation is very poor power efficiencies. One of the ways that they ensure this is by running the cable power amplifier strictly within its linear region. The service providers have to ensure the highest quality in-band transmission conduit so that they can leverage the maximum data throughputs. In-band distortions are, however, of critical importance. Out-of-band (OOB) distortions are not a major concern. Firstly, it can be regarded as a closed environment what happens in the cable stays in the cable! The operator owns and controls the complete spectrum. One of the prominent control techniques is digitally shaping or predistorting the signal before it gets to the power amplifier so that the nonlinearities in the PA are cancelled. The spill-over effect is particularly important in wireless cellular applications, and adjacent channel leakage ratio-or ACLR, as it is termed-is tightly specified and controlled. The distortion can affect the in-band performance and may also result in unwanted signal spilling over into adjacent channels. When power amplifiers are operated in their nonlinear region, their output becomes distorted. With these benefits come substantial challenges this article dives deep into some of these challenges and provides an overview as to how they may be solved. Transitioning the technology to cable brings substantial benefits in terms of power efficiency and performance. It’s a term that many involved in cellular system networks will be familiar with. This article focuses on one aspect of that evolution-power amplifier (PA) digital predistortion (DPD). New technologies have layered themselves on the existing cable network. Even with the rapid changes in technology and distribution methods, cable has maintained a prominent position as a conduit for the distribution of data. Ultrawideband Digital Predistortion (DPD): The Rewards (Power and Performance) and Challenges of Implementation in Cable Distribution Systems
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