Envelope Tracking Makes Phones Smarter

July 10, 2012
Using envelope-tracking techniques, the efficiency of the power amplifiers found in cellular telephones can be improved.

Power amplifier designers supporting wireless communications aim for high efficiency, often through innovative biasing schemes. These schemes typically use only as much energy as needed by the active devices to meet transmit power requirements. Now, however, there is an easier way to boost the power-added efficiency (PAE) of a power amplifier: through the addition of a Coolteq.L envelope-tracking integrated circuit (IC) from Nujira Ltd. (www.nujira.com). The firm’s recently announced model NCT-L1100 power-supply-modulator chip closely tracks an amplifier’s amplitude or power envelope, dynamically adjusting the supply voltage as needed to consume less power and raise PAE.

Traditional power amplifiers operate with a fixed voltage supply, working with a wide range of input power levels—especially in modern wireless communications systems, with their advanced modulation schemes. The peak-to-average-power ratio (PAPR) of these signals can be large, with optimum efficiency occurring when the power amplifier is operating in compression when driving peak level signals. For lower-level signals, the amplifier is still supplied with a fixed voltage and current, although it may not require as much supply power.

Nujira’s Coolteq.L employs the company’s envelope-tracking (ET) technology, which tracks the signal envelope of a wireless handset transceiver and dynamically modulates the supply feeding the power amplifier. The technology is embodied within the company’s lines of handset and base-station power-supply modulators, offering a high-efficiency alternative to conventional buck-boost DC/DC converters. In addition to tracking the signal envelope, the firm’s ISOGAIN™ envelope-shaping technology enhances the linearity of the power amplifier, all the while maintaining its compressed operation for maximum PAE.

The model NCT-L1100 is the first of Nujira’s Coolteq.L line of power-supply modulators designed for use in small, portable devices. It can operate with voltage supplies from 2.50 to 5.25 V, such as cellular telephone handsets. It can also handle peak current to 1 A and provide average power levels to 1.2 W in support of efficiency as high as 80%. The integrated circuit (IC) features a wide-bandwidth, three-stage current supply, control, and ripple-elimination circuitry within a low-profile WLCSP housing (see figure), allowing for ease of integration within an RF front end or power-amplifier module.

The Coolteq.L family is suitable for use in third-generation (3G) and fourth-generation (4G) cellular handsets. The firm also offers its Coolteq.h line of power-supply modulators for base-station applications. Power-supply modulators are available for bandwidths of 5, 10, and 20 MHz, in support of all cellular communications Long-Term-Evolution (LTE) frequency bands; they also include fast disable/enable functionality for use in time-division LTE (TD-LTE) systems. Side benefits of the reduction in amplifier power consumption include longer battery operating life and less heat produced by the amplifier within a handheld telephone.

As Nujira’s Chief Executive Officer Tim Haynes noted earlier this year, with the introduction of the NCT-L1100, “Battery life has always been a key factor for consumers when it comes to mobile handsets, and it is a regular complaint from users of the latest smartphones. 4G handsets may need to be charged two or three times a day, which will have a catastrophic impact on user adoption.” He added that “the industry consensus is that Envelope Tracking will become the standard PA architecture for the next generation of handsets, because it is the only power optimization technology which delivers high efficiency over the entire spectrum used for 3G and 4G standards. As a result we see the launch of our first commercial chip for mobile handsets as a significant milestone—not just for Nujira, but for the mobile handset sector.”

The Coolteq.L model NCT-L1100 uses the industry-standard OpenET analog envelope interface. The IC conforms to Mobile Industry Processor Interface (MIPI) alliance RF front-end (RFFE) specifications to enable a number of different operating modes, including for ET, average power tracking, bypass, and standby. The power-supply modulator, which can supply outputs from 0.5 to 5.0 V with buck-boost capability, is designed for operating temperatures from -40 to +85°C. Nujira Ltd., Building 1010, Cambourne Business Park, Cambourne, Cambridge CB23 6DP, United Kingdom; (44) 1223-597900, e-mail: [email protected], www.nujira.com.

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