AD604 Datasheet | Analog Devices

Features Ultralow input noise at maximum gain 0.80 nV/√Hz, 3.0 pA/√Hz 2 independent linear-in-dB channels Absolute gain range per channel programmable 0 dB to 48 dB (preamplifier gain = 14 dB) through 6 dB to 54 dB (preamplifier gain = 20 dB) ±1.0 dB gain accuracy Bandwidth: 40 MHz (- 3 dB) Input resistance: 300 kΩ Variable gain scaling: 20 dB/V through 40 dB/V Stable gain with temperature and supply variations Single-ended unipolar gain control Power shutdown at lower end of gain control Drive ADCs directly APPLICATIONS Ultrasound and sonar time-gain controls High performance AGC systems Signal measurement GENERAL DESCRIPTION The AD604 is an ultralow noise, very accurate, dual-channel, linear-in-dB variable gain amplifier (VGA) optimized for timebased variable gain control in ultrasound applications; however, it supports any application requiring low noise, wide bandwidth, variable gain control. Each channel of the AD604 provides a 300 kΩ input resistance and unipolar gain control for ease of use. User-determined gain ranges, gain scaling (dB/V), and dc level shifting of output further optimize performance. Each channel of the AD604 uses a high performance preamplifier that provides an input-referred noise voltage of 0.8 nV/√Hz. The very accurate linear-in-dB response of the AD604 is achieved with the differential input exponential amplifier (DSX-AMP) architecture. Each DSX-AMP prises a variable attenuator of 0 dB to 48.36 dB followed by a high speed fixed-gain amplifier. The attenuator is a 7-stage R-1.5R ladder network. The attenuation between tap points is 6.908 dB and 48.36 dB for the ladder network. The equation for the linear-in-dB gain response is G (dB) = (Gain Scaling (dB/V) × VGN (V)) + (Preamp Gain (dB) - 19 dB) Dual, Ultralow Noise Variable Gain...