Quad VGA with Ultralow Noise Preamplifier and Programmable R

The AD8334 is an ultralow noise, quad channel linear-in-dB variable gain amplifier (VGA). Although optimized for ultrasound systems, it may be used as a low noise variable gain control in any application whose operating frequency is less than 100 MHz.

Included in each channel are an ultralow noise preamp (LNA), an X-AMP® VGA with 48 dB of gain range, and a selectable gain postamp 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 AD8334 is a quad version of the single AD8331 and dual AD8332.

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: 100 MHz

* Low power: 145 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

* Optimized for 10-bit/12-bit ADCs

* Selectable output clamping level

* Single 5 V supply operation

* AD8332 and AD8334 available in lead frame chip scale package