Polar Impact™ Technology

The Tropian® Polar Impact™ technology specifically addresses the challenges faced by manufacturers of multimode handsets by taking an entirely different approach to the RF platform. Tropian's radio transceiver products use this novel transmit architecture, while combining the acknowledged advantages of a direct conversion receiver.

The traditional quadrature modulator approach, requires a linear power amplifier with conflicting demands between improving power efficiency or maintaining linearity. Compromising linearity, causes adjacent channel degradation, which can be a fundamental factor in limiting network performance and capacity. Additional problems with device parametric restrictions, temperature instability, power control accuracy, wideband noise and production yields are also common.

Tropian's Polar Impact™ technology, is a unique RF architecture which can be largely implemented in digital logic. It is amenable to high levels of integration on standard, high-volume, foundry CMOS processes. Digital implementations are inherently more immune to performance changes due to temperature, supply, processes variations and aging. Measurement data from Tropian's handset products display RF spectral performance that can approach those needed for stringent base stations requirements, but with the low power consumption levels well suited for the mobile environment.

This excellent RF performance provides considerable margin to the required specifications set by international standards bodies like ETSI and 3GPP, making end-systems containing Tropian products very robust. The design facilitates the implementation of different modulation standards (GMSK, 8-PSK, QAM/W-CDMA) in the same platform without fundamentally changing the system architecture. Different modulation schemes can be satisfied by simply changing the digitally encoded coefficients in the transceiver.

Tropian's patented Polar Impact™ technology is featured in the Tropian Timestar™, Codestar™ and Multistar™ lines of products.

Polar Impact™ Diagram

Technology Differentiation

Fundamental to Polar Impact™ technology, is the principle that a "switch" is the appropriate circuit element as the basis for a very power-efficient radio circuit design. An immediate consequence of this decision is a natural implementation of Tropian products using digital CMOS technology. After all, one of the best switch circuits ever invented is a CMOS digital gate. This allows the digital implementation to extend much closer to the antenna than is usually the case for an analog transmitter, where the transition to analog occurs quite early at the I and Q outputs from the baseband IC.

More importantly, this switch-based circuit topology must also include the power amplifier operating at the higher radio frequencies. This holds true even for information-efficient modulation schemes such as those used for W-CDMA and 802.11a/g WLAN. Tropian's approach is the antithesis of conventional PA circuit design. A Tropian designed radio violates nearly every rule that is normally followed by conventional PA designers. Not surprisingly, Tropian’s reference radio solution also exhibits very different characteristics to those based on a conventional linear PA (even one that is operated in a somewhat nonlinear manner to improve its efficiency).

Polar modulation as a radio transmission technique can be traced back to 1917. For example, from the mid 1920's through the 1980's a variant of polar technology called plate modulation was used in every AM broadcast transmitter. Although the concept of polar modulation is not new, the ability of using polar technology to achieve the signal modulation accuracies and power control dynamic ranges required of modern cellular communication systems is very new.

"Not all Polar schemes are created equal"

Much of the early work to improve the accuracy of Polar modulated transmitters involved the application of feedback loops around the PA and modulators. These techniques, known collectively as Polar Loops, are outlined in Figure 1 below. Polar Loop technologies were initially considered for adoption by Tropian engineers but rejected for several reasons. Chief among them being the inherent need for a precision receiver for feedback for one’s own transmitter. This precision receiver has to be in addition and is separate from the normal handset receiver. So its inclusion further complicates the entire product design with corresponding increase in power consumption, diesize and cost. The “Polar Loop” approach was deemed unacceptable, as it would not support our desired goals to provide enhanced performance at highest levels of integration.

Figure 1: A Polar Loop architecture, showing the required precision receiver (RX) as a part of the complete transmitter

Tropian's Unique Polar Impact™ Technology Advantage

Tropian therefore pioneered methods where RF feedback would not be needed around the PA, which we call Direct Polar technology. Using Direct Polar technology (Polar Impact™) the complexities and drawbacks of polar loop designs are eliminated, as seen by comparing the direct polar implementation in Figure 2 to the polar loop of Figure 1. This technique does require that the PA be controlled to operate in a very predictable and consistent manner. Now with over 6 years of characterization and validation testing complete, Tropian's methods of controlling the PA in the required manner are proven.

Figure 2: The Direct Polar transmitter, with a much simpler structure and realization than a Polar Loop

One platform for one world

The experienced team developing Tropian's Polar Impact™ technology determined early on that there would be tremendous value in the ability to scale product designs in both signal bandwidth and output power. The signal bandwidth scalability is a major reason, why Tropian's products can successfully support multiple operating modes, such as GSM, EDGE, and W-CDMA. To this list we have also successfully realized the signals for AMPS, ANSI-136 (TDMA), 802.11b (Wi-Fi), 802.11g (OFDM), IS-95 (cdmaOne®), cdma2000 1xRTT, Bluetooth, and several others. Measured signal spectra for six of these signals are presented in Figure 3.

Figure 3: Measured signal spectra

Polar Impact™: A flexible and scalable platform

With nearly 2 billion users worldwide, there is no doubt, that mobile communications continues to revolutionize the world and the way we live. There is a new generation of people that has grown up, expecting easy, affordable, instant, multimedia communications anytime, anywhere. The demand for access to increasing amounts of information and new services shows no sign of stopping. Mobile communication standards are evolving beyond 3G and innovative 'convergence' products are being designed with various combinations of cellular wireless standards, WiFi, Bluetooth, etc. Consequently, handset terminals have to grow in sophistication and capability as they cater to these trends and emerging applications.

Whatever the future holds – It's multimode! Tropian's Polar Impact™ technology is even more compelling when one considers the benefits it brings when applied to multi-mode terminals. As more complex modulation schemes are deployed and multiple interface standards crammed into handsets, Tropian's Polar Impact™ architecture has the intrinsic flexiblity and scalabality to provide solutions with superior performance and unprecendented level of integration.

Tropian's innovative Polar Impact™ technology can be used in many more applications beyond mobile handsets. These range from wireless basestations, WLAN to WiMAX/WiBRO equipment. Polar Impact™ technology provides excellent performance across many modulation schemes including GMSK, PSK, QAM, OFDM which are the basis for many common communication physical layer standards.