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1.2GSps DAC supports up to 400MHz bandwidth

Posted: 12 Oct 2009 ?? ?Print Version ?Bookmark and Share

Keywords:DAC? broadband? W-CDMA? WiMAX?

AD9122 DAC

Analog Devices Inc. has developed a dual-channel, 1.2GSps, 16bit DAC that supports the high data rates and complex modulation schemes required for advanced multicarrier wireless and broadband communications equipment.

Featuring an on-chip 32bit numerically-controlled oscillator (NCO) that allows flexible placement of the IF to help optimize system performance, ADI's AD9122 DAC satisfies requirements for multi-standard cellular base stations and other applications that use digital pre-distortion (DPD) techniques demanding broad signal bandwidths. The wireless communications standards that the AD9122 supports include GSM, W-CDMA, TD-SCDMA, CDMA2000, WiMAX, and LTE.

The combination of the AD9122 dual DAC and ADI's ADL5375 quadrature modulator and AD9516 14-output clock generator meets or exceeds six multicarrier GSM specifications for intermodulation distortion (IMD) and SNR. This signal chain is available as an evaluation board. Other complementary parts include the recently announced ADRF6702 quadrature modulator and ADRF6602 Rx mixer.

The AD9122 LVDS interface with an eight-word-deep FIFO memory supports a maximum sample-data-input-rate of 1.2GSps and 600MSps per DAC to support signal bandwidths up to 400MHz in advanced DPD transmitter architectures. The data interface supports word, byte, and nibble load allowing customers to reduce input pins on lower data rates to save board space, power and cost. The AD9122 includes an improved on-chip PLL with lower jitter and phase noise. Operating with the on-chip PLL at a DAC output frequency of 150MHz, the AD9122 delivers a 76dB ACLR for single-carrier W-CDMA applications. For the most demanding wireless communications applications, the AD9122 can achieve 83dBc ACLR using an external PLL.

The combination of input data rates, high DAC sample rates, and fine modulation with the integrated NCO, gives system designers flexibility when choosing DAC output frequencies. This is especially helpful in meeting four- to six-carrier GSM transmission specifications and other communications standards.

The AD9122 includes integrated interpolation filters with selectable interpolation factors of 2, 4, and 8. The dual DAC also integrates 32bit NCOs and is available in a space-saving 72-pin LFCSP that is 50 percent smaller than previous generation DACs.

ADI's Data Pattern Generator (DPG2) is a bench-top instrument for driving vectors into its high-speed DACs. The DPG2 connects to a PC over USB and allows a user to download a vector from their PC into the DPG2's internal memory. Once downloaded, the DPG2 can run the vector at full speed via an attached evaluation board for a specific DAC. This allows for rapid evaluation of the DAC with both generic and customer-generated test data.

- Henri Arnold
EE Times Europe

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