Nujira Sets World Record For ET PA Linearity Without Use Of DPD

Nujira’s patented ISOGAIN linearization achieves -50 dBc ACPR and 60% efficiency for LTE signal at 29 dBm, with no computational overhead.

Nujira Ltd, the world leader in Envelope Tracking (ET) technology, has recently released performance results for an LTE handset RF Power Amplifier (PA) which achieves an Adjacent Channel Power Ratio (ACPR) better than -50 dBc and an efficiency of 60% with an LTE waveform, without the use of Digital Pre-Distortion (DPD). The measurements were made using Nujira’s patented ISOGAIN technique to linearize the amplifier in combination with Nujira’s high performance Coolteq ET power supply modulator.  The results exceed the regulatory requirements for 4G LTE terminals by a factor of 100 (20 dB).

“In addition to the well-publicised power saving benefits of ET, the ability to linearize the PA at no extra cost, power or complexity is a huge benefit for smartphone OEMs and chipset vendors”, said Tim Haynes, Nujira’s CEO.  “Our chipset partners can reduce or eliminate the cost, power consumption and development complexity associated with Digital Pre-Distortion in handset applications, giving them significant competitive and time-to-market advantage”.

The traditional approach to correct nonlinearities in RF PAs has been to apply computationally intensive Digital Pre Distortion to the I/Q signals which drive the RF input to the PA, in order to precisely ‘cancel out’ the nonlinear response of the PA. This requires significant digital logic, and complex software algorithms which adapt the correction coefficients as the PA’s RF performance varies with power levels and temperature.

Nujira’s ISOGAIN ET approach instead uses the power supply pin of the PA to directly linearize the PA, and works by adapting the supply voltage at high speed to keep the gain constant as the RF amplitude is modulated.  The mapping between instantaneous RF drive level and instantaneous supply voltage is static, and is stored in a lookup table in the modem chipset.  The mapping applied on a sample-by-sample basis to a magnitude signal calculated from I&Q, and fed to a high speed D/A converter controlling the ET power supply.

“ET introduces a disruptive shift into the RF front end – the characteristics of the PA are now precisely controlled by a lookup table in the digital domain, rather than the analog domain” explained Jeremy Hendy, Nujira’s VP Sales and Marketing.  “It’s effectively a software-defined PA.  Although these headline linearity results we’ve achieved are stunning, the designer can choose to trade off some of that linearity for further efficiency savings, simply by loading a different set of numbers into the shaping table.”

The linearity results were obtained from a Gallium Arsenide (GaAs) PA operating in the 800 MHz band.  Energy savings using ET were approximately 500 mW at 29 dBm output power, a 30% reduction in energy consumption.

Nujira has developed significant expertise, tools and intellectual property to allow PA vendors, platform vendors and OEMs to quickly and easily generate the ISOGAIN shaping tables in a matter of minutes.

Nujira will be demonstrating its NCT-L1200 Coolteq.L ET chip, Multi-Mode, Multi-Band reference designs, and development tools at Mobile World Congress in Barcelona from February 25-28th, 2013.

About Nujira
Nujira’s mission is to dramatically improve the energy efficiency of transmitters for 3G and 4G handsets, base stations and TV broadcast applications by reducing the amount of waste energy dissipated as heat in the RF Power Amplifier circuit. 

Nujira’s patented Coolteq Modulator technology dynamically controls the power supply to the circuit in line with the amplitude of the signal, enabling the creation of highly efficient RF Power Amplifiers. Today Coolteq technology powers the industry’s most energy efficient and highest performing 4G base stations and TV broadcast transmitters. Nujira is now applying the same energy efficient technology to smartphones and other portable wireless devices.

A fabless semiconductor company located in Cambridge, UK, with design centres in Cambridge and Edinburgh, Nujira is enabling the design of cost-effective multi-mode, multi-band handsets that deliver faster data rates, longer battery life, and better coverage. For more information, visit www.nujira.com.