ADI AD8339多普勒超声诊断解决方案

低功耗便携式连续波(CW)多普勒超声诊断设备要求在只能提供非常微弱信号的条件下测量血液流动数据。由于血流量低或测量目标和传感器之间的距离远(例如在胎儿监测或过度肥胖情况下)，输入信号幅度有限，因此要求接收器信号链具有非常大的动态范围。CW同相(I)和正交(Q)调制接收器以及ADC必须适应印制电路板(PCB)尺寸越来越小同时保持低功耗。

在便携式超声设备前端中，模拟信号处理组件是决定总体系统性能和限制的关键。为了增加信道密度，ADI公司提供了多种高集成度、低功耗解决方案，它们能在超小封装内提供超凡的性能。AD8339四正交解调器和移相器通过替代在相位阵列波束形应用中通常使用的大交叉开关矩阵和模拟延时线，比同类产品节省了75%的PCB面积。AD8339每通道功耗仅为73 mW，适合于便携式超声诊断设备使用。该器件节省功耗特性能使设计师可以在车载超声诊断设备中增加信道密度，每信道使用数百个移相器。AD8339采用40引脚LFCSP封装。

AD7980 16 bit PulSAR®低功耗ADC对AD8339 的4通道同相和正交(I/Q)模拟信号分别求和并且以高达1 MSPS采样速率完成模数转换。该器件消耗最小的功耗，占用最小的PCB面积，同时提供高达91.5 dB @1 MSPS无与伦比的SNR。AD7980以1 MSPS全速率工作时功耗仅为7 mW，而且在转换过程中无流水线延迟。该器件通过串行SPI总线提供I/Q数字输出——进一步简化便携式超声设备系统的PCB布线。AD7980采用10引脚MSOP或QFN超小封装。



图1。 AD8339 连接方框图
1．AD8339
The AD8339 is a quad I/Q demodulator configured to be driven by a low noise preamplifier with differential outputs. It is optimized for the LNA in the AD8332/AD8334/AD8335 family of VGAs. The part consists of four identical I/Q demodulators with a 4× local oscillator (LO) input that divides this signal and generates the necessary 0° and 90° phases of the internal LO that drive the mixers. The four I/Q demodulators can be used independently of each other (assuming that a common LO is acceptable) because each has a separate RF input.
Continuous wave (CW) analog beamforming (ABF) and I/Q demodulation are combined in a single 40-lead ultracompact chip scale device, making the AD8339 particularly applicable in high density ultrasound scanners. In an ABF system, time domain coherency is achieved following the appropriate phase alignment and summation of multiple receiver channels. A reset pin synchronizes multiple ICs to start each LO divider in the same quadrant. Sixteen programmable 22.5° phase increments are available for each channel. For example, if Channel 1 is used as a reference and Channel 2 has an I/Q phase lead of 45°, then the user can phase align Channel 2 with Channel 1 by choosing the correct code.

The mixer outputs are in current form for convenient summa-tion. The independent I and Q mixer output currents are summed and converted to a voltage by a low noise, high dynamic range, current-to-voltage (I-V) transimpedance amplifier, such as the AD8021 or the AD829. Following the current summation, the combined signal is applied to a high resolution analog-to-digital converter (ADC), such as the AD7665 (16-bit, 570 kSPS).

An SPI-compatible serial interface port is provided to easily program the phase of each channel; the interface allows daisy chaining by shifting the data through each chip from SDI to SDO. The SPI also allows for power-down of each individual channel and the complete chip. During power-down, the serial interface remains active so that the device can be programmed again.

The dynamic range is typically 160 dB/Hz at the I and Q outputs. The AD8339 is available in a 6 mm × 6 mm, 40-lead LFCSP and is specified over the industrial temperature range of −40°C to +85°C.

主要性能：
Quad integrated I/Q demodulator
16 phase select on each output (22.5° per step)
Quadrature demodulation accuracy
Phase accuracy: ±1°
Amplitude balance: ±0.25 dB
Bandwidth
4LO: LF to 200 MHz
RF: LF to 50 MHz
Baseband: determined by external filtering
Output dynamic range: 160 dB/Hz
LO drive: >0 dBm (50 Ω), single-ended sine wave
Supply: ±5 V
Power consumption: 73 mW/channel (290 mW total)
Power-down via SPI (each channel and complete chip)
应用：
Medical imaging (CW ultrasound beamforming)
Phased array systems
Radar
Adaptive antennas
Communication receivers



图2。AD8339 方框图

2．16-Bit, 1 MSPS PulSAR ADC in MSOP/QFN AD7980
The AD7980 is a 16-bit, successive approximation, analog-to-digital converter (ADC) that operates from a single power supply, VDD. It contains a low power, high speed, 16-bit sampling ADC and a versatile serial interface port. On the CNV rising edge, it samples an analog input IN+ between 0 V to REF with respect to a ground sense IN−. The reference voltage, REF, is applied externally and can be set independent of the supply voltage, VDD. Its power scales linearly with throughput.

The SPI-compatible serial interface also features the ability, using the SDI input, to daisy-chain several ADCs on a single, 3-wire bus and provides an optional busy indicator. It is compatible with 1.8 V, 2.5 V, 3 V, or 5 V logic, using the separate supply VIO.
The AD7980 is housed in a 10-lead MSOP or a 10-lead QFN1 (LFCSP) with operation specified from −40°C to +125°C.

主要特性：
16-bit resolution with no missing codes
Throughput: 1 MSPS
Low power dissipation: 7.0 mW @ 1 MSPS, 70 μW @ 10 kSPS
INL: ±0.6 LSB typical, ±1.25 LSB maximum
SINAD: 91.25 dB @ 10 kHz
THD: −110 dB @ 10 kHz
Pseudo differential analog input range
0 V to VREF with VREF between 2.5 V to 5.5 V
Any input range and easy to drive with the ADA4841
No pipeline delay
Single-supply 2.5 V operation with 1.8 V/2.5 V/3 V/5 V
logic interface
Serial interface SPI-/QSPI™-/MICROWIRE™-/DSP-compatible
Daisy-chain multiple ADCs and busy indicator
10-lead MSOP and 10-lead, 3 mm × 3 mm, QFN1 (LFCSP),
same space as SOT-23
Wide operating temperature range: −40°C to +125°C
应用：
Battery-powered equipment
Communications
ATE
Data acquisitions
Medical instruments



图3。AD7980应用电路图