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The calibration signal was kept unchanged and the LTE carrier center frequency swept from 50 MHz to 400 MHz in order to assess the frequency behaviour. The resulting image rejection, as shown in Figure 5, shows that at least 30 dB dynamic range improvement is maintained across the two first Nyquist zones. As expected, the image rejection decreases with frequency limited by the contribution of the bandwidth error which is not corrected. Conclusion RF sampling A/D converters are key components for next generation software defined radio systems. Timeinterleaved architecture is leveraged to achieve very high sampling rates and low power consumption at the cost of degraded dynamic range. It has been shown that injecting a constrained calibration signal out of the useful band improves significantly this dynamic range thanks to a low complexity calibration algorithm for gain and timing errors. Measurements on 14/500 Msps prototype showed an approximate 30 dB dynamic range improvement across the two first Nyquist zones. The proposed method can be used for higher-speed applications as long as the gain/timing mismatch error model remains valid. References 1 Jiangfeng Wu et al., “A 5.4Gsps 12b 500mW Pipeline ADC in 28nm CMOS”, 2013 Symposium on VLSI Circuits Digest of Technical Papers. 2 Vogel, C.; Johansson, H., “Time-interleaved analog-to-digital converters: status and future directions,” ISCAS, May 2006. 3 Laakso, T.I.; Valimaki, V.; Karjalainen, M.; Laine, U.K., “Splitting the unit delay,” Signal Processing Magazine, IEEE , vol.13, no.1, pp.30,60, Jan 1996 4 IDTDAC1653D datasheet: http:// www.idt.com/document/dst/ dac1653d-dac1658d-datasheet 5 IDTF1241 datasheet: http://www.idt. com/document/dst/f1241-datasheet The author, Djamel Haddadi holds the post of Technical Leader - RF, High Speed Data Converters at IDT www.idt.com. High Frequency CMOS Easy implemantation of Envelope- Tracking in RF front ends EasyET from Nujira is a development toolkit that radically simplifies the deployment of envelope tracking ET and enables handset designers to achieve maximum RF front end system performance with minimal design effort. EasyET is a combination of PA characterization tools, reference hardware and a suite of software that reduces ET development time for platform vendors and handset OEMs by up to three months. By maximizing flexibility, EasyET enables rapid development and performance tuning of multiple region-specific RF front end platform configurations. Julian Hildersley, VP of Applications at Nujira, said: “We know ET is a complicated technology to get right. The hardware challenges of ET have largely been resolved, but new demands on the RF front end have made software development much more complex. One of Nujira’s strengths is our system and software expertise and, with the introduction of EasyET, we are streamlining the design flow and removing the software bottlenecks for chipset vendors and handset OEMs. “You can compare ET to the introduction of fuel injection in the automotive industry – while the additional system complexity initially lengthened the development cycle, the technology quickly became universally adopted because the ultimate benefits were too significant to ignore. The benefits of ET are apparent to everyone and EasyET makes unlocking them significantly easier.” ET introduces a new set of variables into the low-level firmware associated with transmit power control, linearization and production calibration. The adoption of ET also coincides with the introduction of more complex multimode multiband (MMMB) power amplifiers (PAs), and the move from GPIO controlled PAs to MIPI RFFE serial control, which now requires vendor-specific programming sequences to control each individual RF front end component. As a result there has been a significant jump in complexity for low-level firmware development to support the RF front end. Software complexity is further increased because platform vendors increasingly need to deliver and support multiple regional reference designs to handset OEMs, with each design supporting a different set of frequency bands and multiple sources of hardware components. EasyET allows a single firmware build to support multiple RF front end configurations and components by simply modifying configuration tables stored in flash memory. EasyET also includes the device characterization and platform configuration tools allowing chipset vendors and OEMs to generate the required configuration tables. The EasyET design flow features a comprehensive set of hardware and software tools that include: • ET Surface Explorer - an advanced ET PA characterization system, which now supports a variety of third party test and measurement platforms, and can also be run on the target hardware platform; • EasyET Configuration Manager - a set of software configuration tools, which make it easy for platform vendors and OEMs to mix and match RF front end components, and export the required control and calibration tables without rewriting any firmware; • EasyET Universal RFFE Driver - a lowlevel software architecture for the RF front end driver, enabling chipset vendors to support multiple components and optimize performance with a single firmware build. All component-specific ET IC, PA and switch parameters (including RFFE timing and programming sequences) are stored together with calibration data in flash-based configuration tables, rather than being hard-coded into the firmware; • Reference designs - this range of reference designs are based on Nujira’s NCT-L1300, a high performance ET IC, and best-in-breed ET PAs from a number of tier 1 suppliers. www.nujira.com www.microwave-eetimes.com Microwave Engineering Europe March-April 2014 13


MWEE MARAPR 2014
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