AD8339是一款四通道
I/Q demodulator，配置为由具有差分输出的低噪声前置
amplifier驱动，并针对AD8332/AD8334/AD8335系列VGA中采用的LNA进行了优化。该器件包含四个完全相同的I/Q解调器并具有4倍本振(LO)输入，可对此信号进行分频并产生驱动混频器所需的内部0°和90°相内部LO。四个I/Q解调器分别采用不同的RF输入，因此彼此完全独立（假定可接受常见LO）。
The AD8339 is ideal for high-density ultrasound scanners because it combines continuous wave (CW) analog beamforming (ABF) and I/Q demodulation in a single 40-pin ultra-compact chip-scale device. In ABF systems, time-domain consistency is achieved through reasonable phase alignment and multi-receiver channel summing. The reset pin synchronizes multiple ICs to start each LO crossover within the same quadrant. Each channel has sixteen programmable 22.5° phase increments. For example, if channel 1 is used as a reference channel and channel 2 is 45° ahead of the I/Q phase, then the user can phase align channel 2 and channel 1 by selecting the correct code.
The mixer output is in the form of current for easy summing. The output currents of the independent I and Q mixers are added and converted into voltage by a low-noise, high dynamic range, current-voltage (I-V) transconductance amplifier such as the AD8021 or AD829. After the current is summed, the combined signal is applied to a high-resolution analog-to-digital converter (ADC), such as the AD7665 (16-bit, 570 kSPS).
The device offers an SPI-compatible serial interface port for easy programming of the phase of each channel; This interface allows data to be moved from SDI to SDO via individual chips, enabling daisy-chained connections. SPI also allows individual channels to be shut down individually as well as the entire chip. During shutdown, the serial interface remains active, allowing the device to be programmed again.
The dynamic range of the I and Q outputs is 160 dB/Hz typical. The AD8339 is available in a 6 mm x 6 mm, 40-pin LFCSP package and is rated for a temperature range of −40°C to +85°C industrial temperatures.
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