ADC Driver from Analog Devices

11th June 2008

Analog Devices

ES Admin

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Analog Devices (ADI) has extended its family of differential amplifiers by introducing a new device with the industry’s best distortion performance at the lowest power consumption for engineers who need maximum performance when driving high-resolution ADCs (analogue-to-digital converters) in communications infrastructure, instrumentation and other high-speed equipment. Optimised to drive today’s high-performance 14- and 16-bit converters, the ADA4939 differential amplifier consumes less than 120 mW of power on a single 3.3-V supply, while achieving 82-dB SFDR (spurious-free dynamic range) at 70 MHz. The new differential amplifier is available in one- and two-channel versions that can drive ADCs with resolutions up to 16 bits, such as ADI’s AD9460 and AD9461 ADCs, and can drive low-power, 14-bit ADCs, such as ADI’s AD9246.

The ADA4939 can be used in either differential-to-differential or single-ended-to-differential configurations. An internal common-mode feedback loop allows the user to independently adjust the ADA4939 output common-mode level to match the input common mode voltage of the ADC, and at the same time achieve exceptional output balance and suppression of even-order harmonics.

The ADA4939 is especially well suited to communications applications, such as cellular base stations using low IF (intermediate frequency) and baseband signal processing at frequencies up to 100 MHz, and where 14- and 16 bit accuracy is required. The two-channel version, the ADA4939-2, is ideal for driving dual ADCs used in I/Q demodulation schemes. It offers low cross-talk of –80 dB at 100 MHz while providing gain and phase matching.

The ADA4939 is fabricated using ADI’s proprietary silicon-germanium (SiGe) complementary bipolar process, enabling it to achieve very low levels of distortion with an input voltage noise of 2.3 nV/rt Hz, as well as –3 dB bandwidth of 1.4 GHz (G=+2) and a slew rate of 5000 V/µS. The ADA4939 is specified to operate over the −40 degrees C to +105 degrees C temperature range for both 3.3-V and 5-V operation.