ad603.pdf

The AD603 is a low noise, voltage-controlled amplifier for use

in RF and IF AGC systems. It provides accurate, pin selectable

gains of –11 dB to +31 dB with a bandwidth of 90 MHz or

+9 dB to +51 dB with a bandwidth of 9 MHz. Any intermediate

gain range may be arranged using one external resistor. The

input referred noise spectral density is only 1.3 nV/ÖHz and power

consumpTIon is 125 mW at the recommended ±5 V supplies.

The decibel gain is “linear in dB,” accurately calibrated, and

stable over temperature and supply. The gain is controlled at a

high impedance (50 MW), low bias (200 nA) differenTIal input;

the scaling is 25 mV/dB, requiring a gain-control voltage of only

1 V to span the central 40 dB of the gain range. An over- and

under-range of 1 dB is provided whatever the selected range. The

gain-control response TIme is less than 1 ms for a 40 dB change.

The differenTIal gain-control interface allows the use of either

differential or single-ended positive or negative control voltages.

Several of these amplifiers may be cascaded and their gain-control

gains offset to optimize the system S/N ratio.

The AD603 can drive a load impedance as low as 100 W with

low distortion. For a 500 W load in shunt with 5 pF, the total

harmonic distortion for a ±1 V sinusoidal output at 10 MHz is

typically –60 dBc. The peak specified output is ±2.5 V minimum

into a 500 W load, or ±1 V into a 100 W load.

The AD603 uses a proprietary circuit topology—the X-AMP™.

The X-AMP comprises a variable attenuator of 0 dB to

–42.14 dB followed by a fixed-gain amplifier. Because of the

attenuator, the amplifier never has to cope with large inputs and

can use negative feedback to define its (fixed) gain and dynamic

performance. The attenuator has an input resistance of 100 W,

laser trimmed to ±3%, and comprises a seven-stage R-2R ladder

network, resulting in an attenuation between tap points of

6.021 dB. A proprietary interpolation technique provides a

continuous gain-control function which is linear in dB.

The AD603A is specified for operation from –40°C to +85°C

and is available in both 8-lead SOIC (R) and 8-lead ceramic

DIP (Q). The AD603S is specified for operation from –55°C to

+125°C and is available in an 8-lead ceramic DIP (Q). The

AD603 is also available under DESC SMD 5962-94572.

FEATURES

“Linear in dB” Gain Control

Pin Programmable Gain Ranges

–11 dB to +31 dB with 90 MHz Bandwidth

+9 dB to +51 dB with 9 MHz Bandwidth

Any Intermediate Range, e.g., –1 dB to +41 dB with

30 MHz Bandwidth

Bandwidth Independent of Variable Gain

1.3 nV/ÖHz Input Noise Spectral Density

60.5 dB Typical Gain Accuracy

MIL-STD-883 Compliant and DESC Versions Available

APPLICATIONS

RF/IF AGC Amplifier

Video Gain Control

A/D Range Extension

Signal Measurement