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| ADI AD8334 超低噪音超声系统方案 | |||||
作者：ADI 文章来源：ADI 点击数： 更新时间：2008-1-8  |
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Ultralow Noise VGAs with Preamplifier and Programmable RIN AD8331/AD8332/AD8334 The AD8331/AD8332/AD8334 are single-, dual-, and quad-channel ultralow noise, linear-in-dB, variable gain amplifiers (VGAs). Optimized for ultrasound systems, they are usable as a low noise variable gain element at frequencies up to 120 MHz. Included in each channel are an ultralow noise preamplifier (LNA), an X-AMP® VGA with 48 dB of gain range, and a selectable gain postamplifier with adjustable output limiting. The LNA gain is 19 dB with a single-ended input and differential outputs. Using a single resistor, the LNA input impedance can be adjusted to match a signal source without compromising noise performance. The 48 dB gain range of the VGA makes these devices suitable for a variety of applications. Excellent bandwidth uniformity is maintained across the entire range. The gain control interface provides precise linear-in-dB scaling of 50 dB/V for control voltages between 40 mV and 1 V. Factory trim ensures excellent part-to-part and channel-to-channel gain matching. Differential signal paths result in superb second- and third-order distortion performance and low crosstalk. The VGA’s low output-referred noise is advantageous in driving high speed differential ADCs. The gain of the postamplifier can be pin selected to 3.5 dB or 15.5 dB to optimize gain range and output noise for 12-bit or 10-bit converter applications. The output can be limited to a user-selected clamping level, preventing input overload to a subsequent ADC. An external resistor adjusts the clamping level. The operating temperature range is −40°C to +85°C. The AD8331 is available in a 20-lead QSOP package, the AD8332 is available in 28-lead TSSOP and 32-lead LFCSP packages, and the AD8334 is available in a 64-lead LFCSP package. 主要特性： Ultralow noise preamplifier Voltage noise = 0.74 nV/√Hz Current noise = 2.5 pA/√Hz 3 dB bandwidth AD8331: 120 MHz AD8332, AD8334: 100 MHz Low power AD8331: 125 mW/channel AD8332, AD8334: 145 mW/channel Wide gain range with programmable postamp −4.5 dB to +43.5 dB +7.5 dB to +55.5 dB Low output-referred noise: 48 nV/√Hz typical Active input impedance matching Optimized for 10-bit/12-bit ADCs Selectable output clamping level Single 5 V supply operation AD8332 and AD8334 available in lead frame chip scale package 主要应用： Ultrasound and sonar time-gain controls High performance AGC systems I/Q signal processing High speed, dual ADC drivers  图1。 AD8334 功能方框图  图2。 AD8334 信号流程方框图 AD8334评估工具AD8334-EVAL GENERAL DESCRIPTION The AD8334-EVAL is a platform for the test and evaluation of the AD8334 variable gain amplifier (VGA). The board is shipped assembled and tested, and users only need to connect the signal and VGAIN sources and a single 5 V power supply. Figure 1 is a photograph of the board. AD8334-EVAL主要特性： Factory tested Provisions for direct measurement Optional differential-to-single-ended output Provision for LNA output measurement Selectable high or low gain Provision for input calibration Provision for clamping resistors Single-supply operation 应用： Test gain interface circuitry Evaluate clamping characteristics Evaluate effects of dynamic drive signals TGC evaluate system characteristics Medical ultrasound systems Industrial ultrasound systems PC layout guidance Evaluate performance with real-world signals  图3。AD8334-EVAL外形图  图4。AD8334-EVAL板电路图。 |
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