Producing antenna frequencies directly from the transmit DAC output has long been one of the goals for the software-defined radio (SDR) implementation due to myriad advantages for transmit signal chain design. Achieving direct RF output from the DAC saves board space by eliminating upconvert mixer stages and filters and also saves power by enabling the use of a real vs. complex architecture scheme.

The new AD9739, a 14-bit, 2500 MSPS TxDAC transmit DAC, makes generating a direct RF output a reality. The AD9739 features ADI's highest performance DAC core, coupled with MixMode™ super Nyquist operation that enables direct RF output at up to 2.5 GHz and 3.6 GHz in the third Nyquist zone. This mode provides internal digital processing that allows output frequency placement into the second and third Nyquist zones without the traditional sin(x)/x roll-off in signal amplitude. In fact, with the mixer mode function enabled, the power of the images located in the second and third Nyquist zones are boosted to be the strongest in the output spectrum. A band-pass filter can be employed to select either the upper or lower side band signal as the signal of interest. This approach effectively eliminates a mixer stage from the system, reducing cost and board area.

The AD9739 also operates as a traditional high performance DAC generating wideband signals at up to 1 GHz with an SFDR of 60 dB at 950 MHz output. The device includes a dual-bus LVDS interface with on-chip termination, which is interleaved internally into a single datapath to the DAC. This feature eases the interface speed requirements down to 625 MHz double-data rate (DDR) at a DAC sampling rate of 2500 MSPS with double-data rate DDR. The AD9739 is also power efficient, drawing only 1.1 W when running at its full sampling rate. The device is packaged in 160-lead CSP_BGA.

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AD9739 Features

• RF synthesis support
  • Mixer mode output
  • RZ modes
• Excellent dynamic performance
  • DOCSIS 3.0 ACLR: 8 QAM carriers
  • 72 dB @ 90 MHz IF
  • 68.5 dB @ 920 MHz IF
• Dual port LVDS interface with on-chip 100 Ω resistor
• Built-in self-test capabilities
  • LVDS sampling integrities
  • LVDS-to-DAC data transfer integrity
• Low power: 1.1 W @ 2.5 GSPS

Highly Integrated Input/Output Port Eases Design of High Density Optical Line Cards

One challenge in designing optical line cards is consolidating the required monitoring and control circuitry into a limited amount of space. An optical line card can contain many channels, and each channel has several parameters that require monitoring and control. To achieve optimum optical performance, many ADCs and DACs are typically required. In some cases additional signal conditioning circuitry is also necessary. When this analog circuitry is implemented discretely, these components use up valuable board space.

The AD5590 integrates ADCs, DACs, and operational amplifiers in a single 10 mm × 10 mm CSP_BGA package to deliver a compact solution. The device comprises a 16-input channel, 12-bit ADC, 16 DACs (12-bit), and eight uncommitted operational amplifiers, which can be used for biasing, signal conditioning, or independent circuitry, as required. The ADC has a 1 MSPS throughput rate, wide bandwidth, and a typical SNR of 70 dB. The 16 rail-to-rail DACs are operated as two groups of eight whereby each group has its own on-chip 2.5 V reference. The ADC and DAC blocks have individual SPIcompatible interfaces, which can be operated independently to give the customer additional flexibility.

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