ad603.pdf

The AD603 is a low noise, voltage-controlled amplifier for usein RF and IF AGC systems. It provides accurate, pin selectablegains 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 intermediategain range may be arranged using one external resistor. Theinput referred noise spectral density is only 1.3 nV/ÖHz and powerconsumpTIon is 125 mW at the recommended ±5 V supplies.The decibel gain is “linear in dB,” accurately calibrated, andstable over temperature and supply. The gain is controlled at ahigh 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- andunder-range of 1 dB is provided whatever the selected range. Thegain-control response TIme is less than 1 ms for a 40 dB change.The differenTIal gain-control interface allows the use of eitherdifferential or single-ended positive or negative control voltages.Several of these amplifiers may be cascaded and their gain-controlgains offset to optimize the system S/N ratio.The AD603 can drive a load impedance as low as 100 W withlow distortion. For a 500 W load in shunt with 5 pF, the totalharmonic distortion for a ±1 V sinusoidal output at 10 MHz istypically –60 dBc. The peak specified output is ±2.5 V minimuminto 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 theattenuator, the amplifier never has to cope with large inputs andcan use negative feedback to define its (fixed) gain and dynamicperformance. The attenuator has an input resistance of 100 W,laser trimmed to ±3%, and comprises a seven-stage R-2R laddernetwork, resulting in an attenuation between tap points of6.021 dB. A proprietary interpolation technique provides acontinuous gain-control function which is linear in dB.The AD603A is specified for operation from –40°C to +85°Cand is available in both 8-lead SOIC (R) and 8-lead ceramicDIP (Q). The AD603S is specified for operation from –55°C to+125°C and is available in an 8-lead ceramic DIP (Q). TheAD603 is also available under DESC SMD 5962-94572. FEATURES“Linear in dB” Gain ControlPin Programmable Gain Ranges–11 dB to +31 dB with 90 MHz Bandwidth+9 dB to +51 dB with 9 MHz BandwidthAny Intermediate Range, e.g., –1 dB to +41 dB with30 MHz BandwidthBandwidth Independent of Variable Gain1.3 nV/ÖHz Input Noise Spectral Density60.5 dB Typical Gain AccuracyMIL-STD-883 Compliant and DESC Versions AvailableAPPLICATIONSRF/IF AGC AmplifierVideo Gain ControlA/D Range ExtensionSignal Measurement