Datasheet AD603 (Analog Devices)

Low Noise, 90 MHz Variable Gain Amplifier Data Sheet AD603 FEATURES
The decibel gain is linear in dB, accurately calibrated, and stable over temperature and supply. The gain is controlled at a high
Linear-in-dB gain control
impedance (50 MΩ), low bias (200 nA) differential input; the
Pin-programmable gain ranges −11 dB to +31 dB with 90 MHz bandwidth
scaling is 25 mV/dB, requiring a gain control voltage of only
9 dB to 51 dB with 9 MHz bandwidth
1 V to span the central 40 dB of the gain range. An overrange
Any intermediate range, for example −1 dB to +41 dB
and underrange of 1 dB is provided whatever the selected range.
with 30 MHz bandwidth
The gain control response time is less than 1 μs for a 40 dB change.
Bandwidth independent of variable gain
The differential gain control interface allows the use of either
1.3 nV/√Hz input noise spectral density
differential or single-ended positive or negative control voltages.
±0.5 dB typical gain accuracy
Several of these amplifiers may be cascaded and their gain

control gains offset to optimize the system SNR.
APPLICATIONS
The AD603 can drive a load impedance as low as 100 Ω with low distortion. For a 500 Ω load in shunt with 5 pF, the total
RF/IF AGC amplifiers
harmonic distortion for a ±1 V sinusoidal output at 10 MHz is
Video gain controls
typically −60 dBc. The peak specified output is ±2.5 V minimum
A/D range extensions Signal measurements
into a 500 Ω load.

The AD603 uses a patented proprietary circuit topology—the X-AMP®. The X-AMP comprises a variable attenuator of 0 dB
GENERAL DESCRIPTION
to −42.14 dB followed by a fixed-gain amplifier. Because of the The AD603 is a low noise, voltage-controlled amplifier for use attenuator, the amplifier never has to cope with large inputs and in RF and IF AGC systems. It provides accurate, pin-selectable can use negative feedback to define its (fixed) gain and dynamic gains of −11 dB to +31 dB with a bandwidth of 90 MHz or +9 dB to performance. The attenuator has an input resistance of 100 Ω, 51+ dB with a bandwidth of 9 MHz. Any intermediate gain laser trimmed to ±3%, and comprises a 7-stage R-2R ladder range may be arranged using one external resistor. The input network, resulting in an attenuation between tap points of referred noise spectral density is only 1.3 nV/√Hz, and power 6.021 dB. A proprietary interpolation technique provides a consumption is 125 mW at the recommended ±5 V supplies. continuous gain control function that is linear in dB. The AD603 is specified for operation from −40°C to +85°C.
FUNCTIONAL BLOCK DIAGRAM SCALING PRECISION PASSIVE FIXED-GAIN REFERENCE INPUT ATTENUATOR AMPLIFIER GPOS VOUT VG GNEG 6.44kΩ* GAIN- AD603 CONTROL FDBK INTERFACE 694Ω* 0dB –6.02dB –12.04dB –18.06dB –24.08dB –30.1dB –36.12dB –42.14dB VINP R R R R R R R 20Ω* 2R 2R 2R 2R 2R 2R R COMM R-2R LADDER NETWORK
001
*NOMINAL VALUES.
00539- Figure 1.
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Document Outline Features Applications General Description Functional Block Diagram Revision History Specifications Absolute Maximum Ratings ESD Caution Pin Configurations and Function Descriptions Typical Performance Characteristics Test Circuits Theory of Operation Noise Performance The Gain Control Interface Programming the Fixed-Gain Amplifier Using Pin Strapping Using the AD603 in Cascade Sequential Mode (Optimal SNR) Parallel Mode (Simplest Gain Control Interface) Low Gain Ripple Mode (Minimum Gain Error) Applications Information A Low Noise AGC Amplifier Caution Evaluation Board Outline Dimensions Ordering Guide