FDAs bring AC performance to DC-coupled applications

18th November 2014

Siobhan O'Gorman

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Two FDAs (Fully Differential Amplifiers), which provide DC-coupled applications with AC performance to improve system capabilities and overall performance, have been released by Texas Instruments. According to the company, the LMH3401 and LMH5401 FDAs provide higher bandwidth and slew rate, and lower distortion than existing ADC drivers.

The devices enable radar systems that help keep populations safer and wireless base stations that drop fewer calls, while providing faster upload speeds. The LMH3401 provides 16dB of gain and a 30% reduction in both size and power consumption. The FDA delivers 7GHz of -3dB bandwidth at 16dB gain, a high slew rate of 18,000V/μs and low harmonic distortion of -77dBc at 500MHz.

The LMH5401 can be configured for 6dB of gain or more, delivering 6.2GHz of -3dB bandwidth at 12dB gain. The FDA has a slew rate of 17,500V/μs, harmonic distortion of -90dBc at 200MHz and IMD3 of -90dBc at 200MHz.

The LMH3401 and LMH5401 enable system designers to track fast edge rates in pulse-based systems such as radar and amplify high frequencies in a continuous RF waveform environment such as a wireless base station, while maintaining low power consumption. The FDAs also allow the system to receive small signals in the presence of large blockers. Eliminating the need for baluns, the devices can convert the signal from single-ended to differential. This reduces the overall BOM, enables wider bandwidth, reduces the system footprint and simplifies design.

The LMH3401 and LMH5401 minimise data converter distortion from true DC to more than 1GHz in receive and transmit applications. This enables system designers to optimise the performance of TI’s highest-speed data converters, such as the 12-bit, 4-GSPS ADC12J4000; 16-bit, 370-MSPS ADC16DX370; and 16-bit, 2.5-GSPS DAC38J84.

TI LDOs can help maximise the performance of the LMH3401 and LMH5401 by offering noise-free positive and negative power rails. The LP5907 enables the LMH3401 to meet today’s RF and analogue circuit requirements by providing low noise, high power supply rejection ratio, low quiescent current and fast-line and load transient response. The TPS7A3001 LDO generates the clean negative rail required for a dual power supply by attenuating upstream ripple.

Evaluation modules are available for both the LMH3401 and LMH5401 at a price of $149. TINA-TI SPICE models and reference designs are also available to quickly simulate system performance.

The LMH3401 and LMH5401 are available in a 14-pin, 2.5x2.5mm QFN package. Suggested retail pricing is $8.95 for the LMH3401 and $7.95 for the LMH5401 in 1,000 unit quantities.