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ADI AD8334 超低噪音超声系统方案

2008-01-04 嵌入式在线收藏 | 打印

ADI公司的AD8331/AD8332/AD8334是单/双/四路超低噪音可变增益放大器（VGA），每路包含了超低噪音预放大器(LNA)，48 dB增益的X-AMP。

        可变增益放大器（VGA），以及可选择增益的输出放大器，因此最适合用于超声波系统。本文介绍了AD8334的主要性能，方框图，信号流程方框图以及评估工具AD8334-EVAL的主要性能和电路图。

        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
vHigh 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