Datasheet AD604 (Analog Devices)

Dual, Ultralow Noise Variable Gain Amplifier AD604 FEATURES FUNCTIONAL BLOCK DIAGRAM PAOx FBKx –DSXx +DSXx VGNx Ultralow input noise at maximum gain 0.80 nV/√Hz, 3.0 pA/√Hz GAIN CONTROL 2 independent linear-in-dB channels AD604 VREF AND SCALING Absolute gain range per channel programmable 0dB TO –48.4dB 0 dB to 48 dB (preamplifier gain = 14 dB) through 6 dB to DIFFERENTIAL PASSIVE INPUT 54 dB (preamplifier gain = 20 dB) PAIx ATTENUATOR AFA OUTx ±1.0 dB gain accuracy R-1.5R 40Ω LADDER NETWORK VOCM Bandwidth: 40 MHz (−3 dB) Input resistance: 300 kΩ 32Ω FIXED GAIN AMPLIFIER Variable gain scaling: 20 dB/V through 40 dB/V 34.4dB 8Ω Stable gain with temperature and supply variations
01 -0
Single-ended unipolar gain control
540
COMx
00
Power shutdown at lower end of gain control
Figure 1.
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, Preamplifier gains between 5 and 10 (14 dB and 20 dB) provide linear-in-dB variable gain amplifier (VGA) optimized for time- overall gain ranges per channel of 0 dB through 48 dB and 6 dB based variable gain control in ultrasound applications; however, through 54 dB. The two channels of the AD604 can be cascaded it supports any application requiring low noise, wide bandwidth, to provide greater levels of gain range by bypassing the preamplifier variable gain control. Each channel of the AD604 provides a of the second channel. However, in multiple channel systems, 300 kΩ input resistance and unipolar gain control for ease of cascading the AD604 with other devices in the AD60x VGA use. User-determined gain ranges, gain scaling (dB/V), and dc family that do not include a preamplifier may provide a more level shifting of output further optimize performance. efficient solution. The AD604 provides access to the output of the preamplifier, allowing for external filtering between the Each channel of the AD604 uses a high performance preamplifier and the differential attenuator stage. preamplifier that provides an input-referred noise voltage of 0.8 nV/√Hz. The very accurate linear-in-dB response of the Note that scale factors up to 40 dB/V are achievable with reduced AD604 is achieved with the differential input exponential accuracy for scales above 30 dB/V. The gain scales linearly in amplifier (DSX-AMP) architecture. Each DSX-AMP comprises decibels with control voltages of 0.4 V to 2.4 V with the 20 dB/V a variable attenuator of 0 dB to 48.36 dB followed by a high scale. Below and above this gain control range, the gain begins speed fixed-gain amplifier. The attenuator is a 7-stage to deviate from the ideal linear-in-dB control law. The gain R-1.5R ladder network. The attenuation between tap points is control region below 0.1 V is not used for gain control. When 6.908 dB and 48.36 dB for the ladder network. the gain control voltage is <50 mV, the amplifier channel is powered down to 1.9 mA. The equation for the linear-in-dB gain response is The AD604 is available in 24-lead SSOP, SOIC, and PDIP G (dB) = packages and is guaranteed for operation over the −40°C to (Gain Scaling (dB/V) × VGN (V)) + (Preamp Gain (dB) – 19 dB) +85°C temperature range.
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Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION PREAMPLIFIER DIFFERENTIAL LADDER (ATTENUATOR) AC COUPLING GAIN CONTROL INTERFACE ACTIVE FEEDBACK AMPLIFIER (FIXED-GAIN AMP) APPLICATIONS INFORMATION ULTRALOW NOISE AGC AMPLIFIER WITH 82 dB TO 96 dB GAIN RANGE ULTRALOW NOISE, DIFFERENTIAL INPUT-DIFFERENTIAL OUTPUT VGA MEDICAL ULTRASOUND TGC DRIVING THE AD9050, A 10-BIT, 40 MSPS ADC EVALUATION BOARD CONNECTING A WAVEFORM TO THE AD604-EVALZ DSX INPUT CONNECTIONS Cascade VGAs to Boost Gain PREAMPLIFIER GAIN OUTPUTS DC OPERATING CONDITIONS EVALUATION BOARD ARTWORK AND SCHEMATIC OUTLINE DIMENSIONS ORDERING GUIDE