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For demodulation purposes, the model TRF3711 demodulator is a highly linear, direct frequency downconverter that integrates balanced I and Q mixers, a programmable lowpass filter, programmable gain amplifier, LO buffers, and phase splitters. It is a quadrature demodulator capable of converting RF signals directly to complex baseband signals, and it exhibits a 1024QAM EVM of 1.1%.

Figure 4(a) shows an experimental test setup with a single receive channel reference design (model TSW6011) with frequency downconversion demodulator, octal model ADS5282 analog-to-digital converter (ADC), and DAC. Figure 4(b) shows the test setup, while Fig. 4(c) shows the 1.1% 56-MHz 1024QAM signal EVM at the cascaded output of the TRF3711 + ADS5282 + DAC5672.

QAM Is Rising: 1024QAM And Beyond, Fig. 4a

QAM Is Rising: 1024QAM And Beyond, Fig. 4b

QAM Is Rising: 1024QAM And Beyond, Fig. 4c

These higher modulation rates grow in importance as wireless communications users increase their use of wireless services for voice, data, and video. To keep pace, wireless systems must use higher QAM levels in base-station backhaul networks operating at microwave frequencies. Higher modulation levels impose increased system challenges, since they are more susceptible to the effects of noise. Fortunately, modern modulator and signal-generation products provide the low noise levels needed—at the higher frequencies required—to support more complex modulation formats and wider-bandwidth applications.

Dr. Habeeb Ur Rahman Mohammed, Applications Engineer, High-Speed Products

Texas Instruments, Inc., 12500 TI Blvd., Dallas, TX 75243; (972) 995-2011

References

1. E. Nesse, “Boosting Long-haul Microwave Capacity with 1024QAM,” EE Times, March 2012.

2. TI Integrated IQ Modulator PLL/VCOs: SLWS224, TRF372017.

3. TI Integrated IQ Demodulators: SLWS2198, TRF371125.

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