a FEATURES Two Channels with Independent Gain Control “Linear in dB” Gain Response Two Gain Ranges: AD600: 0 dB to +40 dB AD602: –10 dB to +30 dB Accurate Absolute Gain: ؎0.3 dB Low Input Noise: 1.4 nV/√Hz Low Distortion: –60 dBc THD at ؎1 V Output High Bandwidth: DC to 35 MHz (–3 dB) Stable Group Delay: ؎2 ns Low Power: 125 mW (max) per Amplifier Signal Gating Function for Each Amplifier Drives High Speed A/D Converters MIL-STD-883 Compliant and DESC Versions Available APPLICATIONS Ultrasound and Sonar Time-Gain Control High Performance Audio and RF AGC Systems Signal Measurement
The AD600 and AD602 dual channel, low noise variable gain amplifiers are optimized for use in ultrasound imaging systems, but are applicable to any application requiring very precise gain, low noise and distortion, and wide bandwidth. Each independent channel provides a gain of 0 dB to +40 dB in the AD600 and –10 dB to +30 dB in the AD602. The lower gain of the AD602 results in an improved signal-to-noise ratio at the output. However, both products have the same 1.4 nV/√Hz input noise spectral density. The decibel gain is directly proportional to the control voltage, is accurately calibrated, and is supplyand temperature-stable. To achieve the difficult performance objectives, a proprietary circuit form—the X-AMP®—has been developed. Each channel of the X-AMP comprises a variable attenuator of 0 dB to –42.14 dB followed by a high speed fixed gain amplifier. In this way, the amplifier never has to cope with large inputs, and can benefit from the use of negative feedback to precisely define the gain and dynamics. The attenuator is realized as a seven-stage R-2R ladder network having an input resistance of 100 Ω, lasertrimmed to ± 2%. The attenuation between tap points is 6.02 dB; the gain-control circuit provides continuous interpolation between these taps. The resulting control function is linear in dB. X-AMP is a registered trademark of Analog Devices, Inc. *Patented.
Dual, Low Noise, Wideband Variable Gain Amplifiers AD600/AD602* FUNCTIONAL BLOCK DIAGRAM GAT1
PRECISION PASSIVE INPUT ATTENUATOR
GAIN CONTROL INTERFACE
RF2 2.24kΩ (AD600) 694Ω (AD602)
0dB –6.02dB –12.04dB –18.06dB
–22.08dB –30.1dB –36.12dB –42.14dB
A1LO R – 2R LADDER NETWORK
FIXED GAIN AMPLIFIER
41.07dB (AD600) 31.07dB (AD602)
The gain-control interfaces are fully differential, providing an input resistance of ~15 MΩ and a scale factor of 32 dB/V (that is, 31.25 mV/dB) defined by an internal voltage reference. The response time of this interface is less than 1 µs. Each channel also has an independent gating facility that optionally blocks signal transmission and sets the dc output level to within a few millivolts of the output ground. The gating control input is TTL and CMOS compatible. The maximum gain of the AD600 is 41.07 dB, and that of the AD602 is 31.07 dB; the –3 dB bandwidth of both models is nominally 35 MHz, essentially independent of the gain. The signal-to-noise ratio (SNR) for a 1 V rms output and a 1 MHz noise bandwidth is typically 76 dB for the AD600 and 86 dB for the AD602. The amplitude response is flat within ± 0.5 dB from 100 kHz to 10 MHz; over this frequency range the group delay varies by less than ± 2 ns at all gain settings. Each amplifier channel can drive 100 Ω load impedances with low distortion. For example, the peak specified output is ± 2.5 V minimum into a 500 Ω load, or ± 1 V into a 100 Ω load. For a 200 Ω load in shunt with 5 pF, the total harmonic distortion for a ± 1 V sinusoidal output at 10 MHz is typically –60 dBc. The AD600J and AD602J are specified for operation from 0°C to +70°C, and are available in both 16-pin plastic DIP (N) and 16-pin SOIC (R). The AD600A and AD602A are specified for operation from –40°C to +85°C and are available in both 16-pin cerdip (Q) and 16-pin SOIC (R). The AD600S and AD602S are specified for operation from –55°C to +125°C and are available in a 16-pin cerdip (Q) package and are MIL-STD-883 compliant. The AD600S and AD602S are also available under DESC SMD 5962-94572.
REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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