Amplifier ICs
Volume 8, Issue 9 YOUR SEMICONDUCTOR SOLUTIONS RESOURCE

Low Power, Ultralow Distortion, Differential ADC Drivers for 14-Bit and 16-Bit ADCs

The ADA4939 and ADA4927 differential ADC drivers offer the industry's best distortion performance at the lowest power consumption for engineers who need maximum performance when driving high resolution ADCs in communications infrastructure, instrumentation, and other high speed equipment.

These differential amplifiers offer resolutions up to 16 bits from dc to 100 MHz and are ideal for driving high performance ADCs such as ADI's AD9460 and AD9461. The devices can also drive low power 14-bit ADCs such as ADI's AD9246. Both the ADA4939 and ADA4927 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 output common-mode level to match the input common-mode voltage of the ADC. At the same time, it achieves exceptional output balance and suppression of even-order harmonics.

The ADA4939-1 (single) and ADA4939-2 (dual) consume less than 120 mW of power on a single 3.3 V supply while achieving 82 dB spurious-free dynamic range at 70 MHz. It can operate on single supplies from 3.3 V to 5 V.

Using a current feedback architecture, the ADA4927-1 (single) and ADA4927-2 (dual) consume only 20 mA quiescent current and can operate on supplies from 5 V to ±5 V while achieving 83 dB SFDR at 70 MHz. The current feedback architecture provides loop gain that is nearly independent of closed-loop gain, thus achieving wide bandwidth, low distortion, and low noise at high gains—all at a lower power consumption than comparable voltage feedback amplifiers.

Both product families are fabricated using ADI's proprietary silicon-germanium (SiGe) complementary bipolar process to enable very low levels of distortion and input voltage noise. Low dc offset and excellent dynamic performance make these parts well suited for a wide variety of data acquisition and signal processing applications.

Both single and dual versions of the ADA4939 and ADA4927 are specified to operate over the –40°C to +105°C temperature range. The single version of both parts is available in a 16-lead LFCSP package; the dual version of both is available in a 24-lead LFCSP package. The pinouts for the ADA4939 and ADA4927 (single and dual versions) have been optimized for PCB layout and minimal distortion and are pin-to-pin compatible with the ADA4937 and ADA4938 differential ADC drivers.

ADA4927-2 ADA4927-1 ADA4939-2 ADA4939-1

ADA4939

ADA4939 Features

  • Low harmonic distortion
    • –102 dBc HD2 @ 10 MHz
    • –83 dBc HD2 @ 70 MHz
    • –77 dBc HD2 @ 100 MHz
    • –101 dBc HD3 @ 10 MHz
    • –97 dBc HD3 @ 70 MHz
    • –91 dBc HD3 @ 100 MHz
  • Input voltage noise:
    2.3 nV/√Hz
  • –3 dB bandwith:
    1 GHz, G = 1
  • Slew rate:
    6800 V/µs, 25% to 75%
  • Fast overdrive
    recovery: <1 ns
  • Offset voltage:
    ±0.5 mV typical
  • Externally adjustable gain
  • Stable for
    differential gains: ≥2

ADA4927 Features

  • Low harmonic distortion
    • –117 dBc HD2 @ 10 MHz
    • –85 dBc HD2 @ 70 MHz
    • –75 dBc HD2 @ 100 MHz
    • –122 dBc HD3 @ 10 MHz
    • –95 dBc HD3 @ 70 MHz
    • –85 dBc HD3 @ 100 MHz
  • Input referred noise:
    1.3 nV/√Hz, 23 pA/√Hz
  • –3 dB bandwith:
    1 GHz, G = 1
  • Slew rate:
    6000 V/µs, 25% to 75%
  • Fast overdrive
    recovery: 2.6 ns
  • Offset voltage:
    1 mV typical
  • Externally adjustable gain
  • 0.1 dB gain flatness:
    250 MHz

Driving today's high performance ADCs can present many difficult challenges. ADI's online seminar provides tips and techniques for maintaining the level of signal integrity needed to meet system objectives. For more information, visit www.analog.com/onlineseminars/adcdriving.

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