AD604

Features:

Two Independent Linear-in-dB Channels
Absolute Gain Range per Channel Programmable:
0 dB to +48 dB (Preamp Gain = +14 dB), through
+6 dB to +54 dB (Preamp Gain = +20 dB)
61.0 dB Gain Accuracy
Bandwidth: 40 MHz (3 dB)
300 kV Input Resistance
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
Can Drive A/D Converters Directly




Application

Ultrasound and Sonar Time-Gain Control
High Performance AGC Systems
Signal Measurement




Pinout








Specifications

Supply Voltage ±VS
Pins 17, 18, 19, 20 (with Pins 16, 22 = 0 V) . . . . . . ±6.5 V
Input Voltages
Pins 1, 2, 11, 12 . . . . . . . . . . . . .VPOS/2 ±2 V Continuous
Pins 4, 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±2 V
Pins 5, 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . VPOS, VNEG
Pins 6, 7, 13, 14, 23, 24 . . . . . . . . . . . . . . . . . . . . VPOS, 0
Internal Power Dissipation
Plastic (N) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 W
Small Outline (R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 W
Shrink Small Outline (RS) . . . . . . . . . . . . . . . . . . . . . 1.1 W
Operating Temperature Range . . . . . . . . 40°C to +85°C
Storage Temperature Range . . . . . . . . . .65°C to +150°C
Lead Temperature, Soldering 60 seconds . . . . . . . +300°C






Description

The AD604 is an ultralow noise, very accurate, dual channel, linear-in-dB variable gain amplifier (VGA) optimized for time-based variable gain control in ultrasound applications; however it will support 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 application performance.

Each channel of the AD604 utilizes 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 of the DSX-AMPs comprise a variable attenuator of 0 dB to 48.36 dB followed by a high speed fixed gain amplifier. The attenuator is based on a seven stage R-1.5R ladder network. The attenuation between tap points is 6.908 dB and 48.36 dB for the ladder network.

Each independent channel of the AD604 provides a gain range of 48 dB which can be optimized for the application by programming the preamplifier with a single external resistor in the preamp feedback path. The linear-in-dB gain response of the AD604 can be described by the equation: G (dB) = (Gain Scaling (dB/V) * VGN (V)) + (Preamp Gain (dB) 19 dB). Preamplifier gains between 5 and 10 (+14 dB and +20 dB)provide overall gain ranges per channel of 0 dB through +48 dB and +6 dB through +54 dB. The two channels of the AD604 can be cascaded to provide greater levels of gain range by bypassing the 2nd channel's preamplifier. However, in multiple channel systems, cascading the AD604 with other devices in the AD60x VGA family, which do not include a preamplifier may provide a more efficient solution. The AD604 provides access to the output of the preamplifier allowing for external filtering between the preamplifier and the differential attenuator stage.