Analog Devices has introduced a highly integrated, 200 MSPS 14-bit quadrature digital upconverter (QDUC) for broadband communications and wireless infrastructure applications.
The single- chip, mixed-signal AD9857 integrates a high-speed direct digital synthesiser (DDS),14-bit DAC, digital filter, clock multiplier circuitry, and user programmability in an 80-lead LQFP. It accepts complex I/Q input data, upsamples the data, quadrature-modulates the data onto a carrier, and outputs a frequency-agile modulated carrier in the analog domain.
‘Unlike any of its predecessors, the AD9857 moves much of the Tx (transmit) path from the analog domain to the digital domain and enables a ‘future-proof’ approach to system partitioning: the RF interface block is physically separate from the digital ASIC,’ said Charles O’Roark, Digital Signal Synthesis Product Line Manager, Analog Devices. ‘This approach allows each block to be optimised, which yields improvement in system performance and flexibility. Changes to interface standards and system enhancements are incorporated in a simple ‘spin’ of the digital ASIC, whereas the RF interface remains the same – hence ‘future-proof’.’
The advantages of an all-digital Tx path include direct processor control, on-the-fly programmability of data rates, precision frequency hopping, and reduced system complexity.
Superior dynamic performance makes the AD9857 ideal for broadband/cable modem return path modulation and cellular basestations. Generating a dc- to 80-MHz digital output from a single 3.3 V supply, the AD9857’s 80-dB narrowband spurious free dynamic range provides the spectral performance needed to upconvert GMSK, CDMA, spread spectrum, OFDM, 256-QAM and any other complex modulation format.
Using an image of the of the AD9857’s output signal can further reduce analog upconvert stages and still meet stringent spectral mask requirements. The AD9857’s stable 14-bit DDS/DAC/Tx architecture includes a 4+ – 20+ programmable reference clock multiplier and PLL lock detect indicator capable of operation in either quadrature modulator, single-tone, interpolating DAC mode or FSK mode.
The AD9857 operates over the extended industrial temperature range (–40ºC to +85ºC), is priced at $15.40 in 10,000-piece quantities (engineering samples and production quantities are available from stock), and packaged in an 80-lead LQFP. Evaluation boards are also available by contacting your nearest Analog Devices sales office.
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