Low-noise, fully differential SAR ADC driver

July 04, 2014 // By Graham Prophet
Maxim has posted details of a low-noise, low-distortion fully differential operational amplifier suitable for driving high-speed, high-resolution, 20-/18-/16-bit SAR analogue-to-digital converters; MAX44205 claims the best-available combination of low power, low noise, THD, and gain bandwidth

Featuring a combination of 2.7 V to 13.2 V supply voltage range and 400 MHz bandwidth, the MAX44205 is suitable for low-power, high-performance data acquisition systems. It has a VOCM input to adjust the output common-mode voltage, eliminating the need for a coupling transformer or AC-coupling capacitors. This adjustable output common-mode voltage allows the MAX44205 to match the input common-mode voltage range of the ADC following it.

A proprietary output voltage clamping solution ensures that the buffer output does not violate the ADC's maximum input voltage range, even if the MAX44205’s supply rails are higher than the ADC’s full-scale range. Shutdown mode consumes 6.8 µA and extends battery life in battery-powered applications or reduces average power in systems cycling between shutdown and periodic data readings.

The MAX44205 is available in 12-pin, 3-mm x 3-mm, TQFN and 10-pin µMAX packages and is specified for operation over the -40°C to +125°C temperature range. Features include;

Low input noise; 3.1nV/ √Hz at 1kHz, 200 nVP-P from 0.1 Hz to 10 Hz

High speed for DC and AC; gain-bandwidth of 400 MHz, -3dB gain-bandwidth, 180 MHz, and slew rate of 180 V/µs.

Ideal for driving AC inputs to 20-bit SAR ADCs; THD = -130 dBc at 10 kHz, V OUT-DIFF = 2 V P-P and THD = -84 dBc at 1 MHz, V OUT-DIFF = 2 V P-P

Typical applications include active filters, fully-differential signal conditioning, high-speed process control, medical imaging, and single-ended to differential conversion.