Maxim MAX2038 8路超声波放大和混合方案

Maxim公司的MAX2038是8路可变增益放大器(VGA)和可编程8路混合阵列,具有高线性高动态范围和低噪音性能,设计用于超声图像和多普勒应用. MAX2038的绝对增益误差小于±0.25dB,差分输出,通过外接班无源抗混淆滤波器能直接驱动超声波ADC, VOUT = 1.5VP-P 和fIN = 5MHz时的二次谐波失真为-70dBc,三次谐波失真为-52dBc.可编程增益范围为42dB.本文介绍了MAX2038的主要特性,功能方框图以及每路超声图像典型应用电路图.

The MAX2038 8-channel variable-gain amplifier (VGA) and programmable octal mixer array is designed for high linearity, high dynamic range, and low noise performance targeting ultrasound imaging and Doppler applications. Each amplifier features differential inputs and outputs and a total gain range of 42dB (typ). In addition, the VGAs offer very low output-referred noise performance suitable for interfacing with 12-bit ADCs.
The MAX2038 VGA is optimized for less than ±0.25dB absolute gain error to ensure minimal channel-to-channel ultrasound beamforming focus error. The device’s differential outputs are designed to directly drive ultrasound ADCs through an external passive anti-aliasing filter. A switchable clamp is also provided at each amplifier’s output to limit the output signals, thereby preventing ADC overdrive or saturation.

Dynamic performance of the device is optimized to reduce distortion to support second-harmonic imaging. The device achieves a second-harmonic distortion specification of -70dBc at VOUT = 1.5VP-P and fIN = 5MHz and an ultrasound-specific*, two-tone, third-order intermodulation distortion specification of -52dBc at VOUT = 1.5VP-P and fIN = 5MHz.
The MAX2038 also integrates an octal quadrature mixer array and programmable LO phase generators for a complete CW beamforming solution. The LO phase selection for each channel can be programmed using a digital serial interface and a single high-frequency clock or the LOs for each complex mixer pair can be directly driven using separate 4 x LO clocks. The serial interface is designed to allow multiple devices to be easily daisy chained to minimize program interface wiring. The LO phase dividers can be programmed to allow 4, 8, or 16 quadrature phases. The input path of each CW mixer consists of a selectable lowpass filter for optimal CWD noise performance. The outputs of the mixers are summed into I and Q differential current outputs. The mixers and LO generators are designed to have exceptionally low noise performance of -155dBc/Hz at 1kHz offset from a 1.25MHz carrier.

The MAX2038 operates from a +5.0V power supply, consuming only 120mW/channel in VGA mode and 269mW/channel in normal power CW mode. A lowpower CW mode is also available and consumes only 226mW/channel. The device is available in a lead-free 100-pin TQFP package (14mm x 14mm x 1mm) with an exposed pad. Electrical performance is guaranteed over a 0C to +70C temperature range.

MAX2038主要特性:
8-Channel Configuration
High Integration for Ultrasound Imaging Applications
Pin Compatible with the MAX2037 Ultrasound VGA VGA Features
Maximum Gain, Gain Range, and Output-Referred Noise Optimized for Interfacing with 12-Bit ADCs Maximum Gain of 29.5dB Total Gain Range of 42dB 22nV/√Hz Ultra-Low Output-Referred Noise at 5MHz
±0.25dB Absolute Gain Error
120mW Consumption per Channel
Switchable Output VGA Clamp Eliminating ADC Overdrive
Fully Differential VGA Outputs for Direct ADC Drive
Variable Gain Range Achieves 42dB Dynamic Range
-70dBc HD2 at VOUT = 1.5VP-P and fIN = 5MHz _ Two-Tone Ultrasound-Specific* IMD3 of -52dBc at VOUT = 1.5VP-P and fIN = 5MHz CW Doppler Mixer Features
_ Low Mixer Noise of -155dBc/Hz at 1kHz Offset from 1.25MHz Carrier
Serial-Programmable LO Phase Generator for 4, 8, 16 LO Quadrature Phase Resolution
Optional Individual Channel 4 x fLO LO Input Drive Capability
269mW Power Consumption per Channel (Normal Power Mode) and 226mW Power Consumption per Channel (Low-Power Mode)
CWD Implementation Is Fully Compliant with All Patents Related to Ultrasound Imaging Techniques
MAX2038应用:
Ultrasound Imaging
Sonar



图1.MAX2038功能方框图



图2.MAX2038 CW混合器和可编波束成形器功能方框图



图3. 每路超声图像典型应用电路图