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FEATURES
2 channels with independent gain control Linear in dB gain response
2 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 (maximum) per amplifier Signal gating function for each amplifier Drive high speed ADCs MIL-STD-883-compliant and DESC versions available
APPLICATIONS
Ultrasound and sonar time-gain controls High performance audio and RF AGC systems Signal measurement
GENERAL DESCRIPTION
The AD600/AD6021 dual-channel, low noise, variable gain amplifiers are optimized for use in ultrasound imaging systems but are applicable to any application requiring 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 (SNR) 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, accurately calibrated, and supply and temperature stable.
To achieve the difficult performance objectives, a proprietary circuit form, the X-AMP®, was 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 7-stage R-2R ladder network having an input resistance of 100 Ω, laser trimmed 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.
1 Patented.
Rev. F
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Dual, Low Noise, Wideband Variable Gain Amplifiers AD600/AD602
FUNCTIONAL BLOCK DIAGRAM
GAT1
SCALING REFERENCE
PRECISION PASSIVE INPUT ATTENUATOR
GATING INTERFACE
C1HI C1LO
VG
GAIN CONTROL INTERFACE
A1HI
0dB
–12.04dB
–22.08dB –36.12dB
–6.02dB –18.06dB
–30.1dB
–42.14dB
A1LO 500Ω
R-2R LADDER NETWORK
62.5Ω
A1OP
A1CM
RF2 2.24kΩ (AD600) 694Ω (AD602) RF1 20Ω
FIXED-GAIN AMPLIFIER 41.07dB (AD600) 31.07dB (AD602)
Figure 1. Functional Block Diagram of a Single Channel of the AD600/AD602
The gain-control interfaces are fully differential, providing an input resistance of ~15 MΩ and a scale.