General-Purpose, Low Cost, DC-Coupled VGA

The AD8337 is a low noise, single-ended, linear-in-dB, general-purpose variable gain amplifier (VGA) usable at frequencies from dc to 100 MHz; the −3 dB bandwidth is 280 MHz. Excellent bandwidth uniformity across the entire gain range and low output-referred noise makes the AD8337 ideal for gain trim applications and for driving high speed analog-to-digital converters (ADCs).

Excellent dc characteristics combined with high speed make the AD8337 particularly suited for industrial ultrasound, PET scanners, and video applications. Dual-supply operation enables gain control of negative-going pulses such as generated by photodiodes or photomultiplier tubes.

The AD8337 uses the popular and versatile X-AMP® architecture, exclusively from Analog Devices, Inc., with a gain range of 24 dB. The gain control interface provides precise linear-in-dB scaling of 19.7 dB/V, referenced to VCOM.

The AD8337 includes an uncommitted operational current-feedback preamplifier (PrA) that operates in inverting or noninverting configurations. Using external resistors, the device can be configured for gains of 6 dB or greater. The AD8337 is characterized by a noninverting PrA gain of 2× using two external 100 Ω resistors. The attenuator has a range of 24 dB, and the output amplifier has a fixed gain of 8× (18.06 dB). The lowest nominal gain range is 0 dB to 24 dB and can be shifted up or down by adjusting the preamp gain. Multiple AD8337s can be connected in series for larger gain ranges, and for interstage filtering to suppress noise and distortion, and for nulling offset voltages.

The operating temperature range is –40°C to +85°C, and it is available in an 8-lead, 3 mm × 3 mm LFCSP.

Applications

* Gain trim

* PET scanners

* High performance AGC systems

* I/Q signal processing

* Video

* Industrial and medical ultrasound

* Radar receivers

* Low noise: Voltage noise = 2.2 nV/√Hz

Current noise = 4.8 pA/√Hz (positive input)

* Wide bandwidth (−3 dB) = 280 MHz

* Nominal gain range: 0 dB to 24 dB (preamp gain = 6 dB)

* Gain scaling: 19.7 dB/V

* DC-coupled

* Single-ended input and output

* High speed uncommitted op amp input

* Supplies: +5 V, ±2.5 V, or ±5 V

* Low power: 78 mW with ±2.5 V supplies