Envelope tracking (ET) describes an approach to

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the u ...

(RF)

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 ...

design in which the

power supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, electric current, current, and frequency to power ...

voltage applied to the RF power amplifier is continuously adjusted to ensure that the amplifier is operating at peak efficiency for power required at each instant of transmission. A conventional RF amplifier designed with a fixed supply voltage operates most efficiently only when operating in compression. Amplifiers operating with a constant supply voltage become less efficient as the crest factor of the signal increases, because the amplifier spends more time operating below peak power and, therefore, spends more time operating below its maximum efficiency.

Background

The need for greater efficiency arises particularly as modulation schemes become more complicated and their peak to average power ratio increases. Older modulation schemes based on phase or

frequency modulation Frequency modulation (FM) is a signal modulation technique used in electronic communication, originally for transmitting messages with a radio wave. In frequency modulation a carrier wave is varied in its instantaneous frequency in proporti ...

with no amplitude information carried on the signal can use amplifiers that are driven into compression and offer high levels of efficiency. As of 2014 mobile communications basestations consumed ~1% of global electricity. In contrast, many new communications systems from WiMAX to LTE ''do'' use amplitude information. The amplifier cannot be run into compression, because the amplitude information becomes distorted. These amplifiers can only achieve their peak efficiency on the peaks of the amplitude. The remainder of the time power is being dissipated unnecessarily. Thus signals with a high peak to average power ratio mean that low efficiency levels are achieved, with the excess energy being wasted, ultimately as heat.

Variable voltage

Envelope tracking adjusts the voltage applied to an RF power amplifier to deliver the power needed at that instant.

Envelope An envelope is a common packaging item, usually made of thin, flat material. It is designed to contain a flat object, such as a letter (message), letter or Greeting card, card. Traditional envelopes are made from sheets of paper cut to one o ...

information is derived from the IQ modem and is passed to an envelope tracking power supply to provide the required voltage. In 2013,

Qualcomm Qualcomm Incorporated () is an American multinational corporation headquartered in San Diego, California, and Delaware General Corporation Law, incorporated in Delaware. It creates semiconductors, software and services related to wireless techn ...

became the first company to ship a chip with such technology, which it claimed to be the industry’s first for 3G and 4G LTE mobile devices. R2 Semiconductor became the industry's first ET company to ship a phone with ET in the Samsung Galaxy S5 Mini.Samsung Galaxy S5 Mini Teardown (see step 15)
. iFixit. Retrieved 4 Sept 2014 As of September 2014, at least 16 phones employ ET, including the

Samsung Samsung Group (; stylised as SΛMSUNG) is a South Korean Multinational corporation, multinational manufacturing Conglomerate (company), conglomerate headquartered in the Samsung Town office complex in Seoul. The group consists of numerous a ...

Galaxy Note 3, Galaxy S5 Mini, Nexus 5, and iPhone 6. Other component makers evaluating the technology include R2 Semiconductor, Mediatek, RF Micro Devices, Skyworks,

Texas Instruments Texas Instruments Incorporated (TI) is an American multinational semiconductor company headquartered in Dallas, Texas. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog ...

Analog Devices Analog Devices, Inc. (ADI), also known simply as Analog, is an American multinational corporation, multinational semiconductor company specializing in data conversion, signal processing, and power management technology, headquartered in Wilming ...

, Nujira and Eta Devices. Eta Devices, an MIT spinoff based in Cambridge, Massachusetts, is preparing a base station module and a chip that it claims decreases battery drain and work well in high-bandwidth applications. The company says the chip helps lower electricity consumption by 20 percent and helps reduce heat generation by up to 30 percent. Eta's approach increases efficiency at the cost of greater signal noise. The company uses advanced

digital signal processing Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are a ...

to handle the problem. The Eta basestation is a little smaller than a shoebox, is the first 4G LTE transmitter to achieve average efficiency greater than 70 percent, up from the typical 45 to 55 percent.

References

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External links

Envelope Tracking Tutorial
includes video and all aspects of envelope tracking
Zhancang Wang, "Envelope Tracking Power Amplifiers for Wireless Communications", Artech House, MA: Boston, 2014.

R2 Semiconductor
Startup working on Envelope Tracking technology Electronic amplifiers