Quad Low Noise, Low Cost Variable Gain Amplifier

The AD8335 is a quad variable gain amplifier (VGA) with low noise preamplifier intended for cost and power sensitive applications. Each channel features a gain range of 48 dB, fully differential signal paths, active input preamplifier matching, and user-selectable maximum gains of 46 dB and 38 dB. Individual gain controls are provided for each channel.

The preamplifier (PrA) has a single-ended to differential gain of ×8 (18.06 dB) and accepts input signals <625 mV p-p. PrA noise is 1.2 nV/√Hz and the combined input referred voltage noise of the PrA and VGA is 1.3 nV/√Hz at maximum gain.

Assuming a 20 MHz noise bandwidth (NBW), the Nyquist frequency for a 40 MHz ADC, the input SNR is 92 dB. The HLxx pin optimizes the output SNR for 10-bit and 12-bit ADCs with 1 V p-p or 2 V p-p full-scale (FS) inputs.

Channel 1 and Channel 2 are enabled through the EN12 pin and Channel 3 and Channel 4 are enabled through the EN34 pin. For VGA only applications, the PrAs can be powered down, significantly reducing power consumption.

The AD8335 is available in a 64-lead lead frame chip scale package (9 mm × 9 mm) for the industrial temperature range of −40°C to +85°C.

Applications

* Medical imaging (ultrasound, gamma cameras)

* Sonar

* Test and measurement

* Precise, stable wideband gain control

Data Sheet, Rev A, 08/2008

* Low noise preamplifier (PrA) * Voltage noise = 1.3 nV/√Hz typical * Current noise = 2.4 pA/√Hz typical * NF = 7 dB (RS = RIN = 50 Ω) * Single-ended input; VIN maximum = 625 mV p-p * Active input match * Input SNR (noise bandwidth = 20 MHz) = 92 dB * VGA Differential output VOUT maximum = 5 V p-p, RL = 500 Ω differential Gain range (8 dB output gain step) −10 dB to +38 dB—low gain mode −2 dB to +46 dB—high gain mode Accurate linear-in-dB gain control * For additional features please see data sheet