Single VGA with Ultralow Noise Preamplifier and Programmable R

The AD8331 is a single channel, ultralow noise, linear-in-dB, variable gain amplifier (VGA). Optimized for ultrasound systems, it is usable as a low noise variable gain element at frequencies up to 120 MHz.

Included is an ultralow noise preamplifier (LNA), an X-AMP® VGA with 48 dB of gain range, and a selectable gain postamplifier with adjustable output limiting. The LNA gain is 19 dB with a single-ended input and differential outputs. Using a single resistor, the LNA input impedance can be adjusted to match a signal source without compromising noise performance.

The 48 dB gain range of the VGA makes these devices suitable for a variety of applications. Excellent bandwidth uniformity is maintained across the entire range. The gain control interface provides precise linear-in-dB scaling of 50 dB/V for control voltages between 40 mV and 1 V. Factory trim ensures excellent part-to-part and channel-to-channel gain matching. Differential signal paths result in superb second- and third-order distortion performance and low crosstalk.

The operating temperature range is -40°C to +85°C. The AD8331 is available in a 20-lead QSOP package.

The AD8331 is a single version of the dual AD8332 and quad AD8334.

For information on specs, see the AD8331/AD8332/AD8334 datasheet.

Applications

* Ultrasound and sonar time-gain controls

* High performance automatic gain control (AGC) systems

* I/Q signal processing

* High speed, dual ADC drivers

* Ultralow noise preamplifier (preamp)

* Voltage noise = 0.74 nV/√Hz

* Current noise = 2.5 pA/√Hz

* 3 dB bandwidth: 120 MHz

* Low power: 125 mW/channel

* Wide gain range with programmable postamp

* −4.5 dB to +43.5 dB in LO gain mode

* 7.5 dB to 55.5 dB in HI gain mode

* Low output-referred noise: 48 nV/√Hz typical

* Active input impedance matching