The AD8333 is a dual phase shifter and
I/Q demodulator, which enables coherent summation and phase alignment of multiple analog data channels. It is the first solid-state device suitable for beamgenerator circuits that can be used in high-performance medical ultrasound devices with continuous-wave Doppler modes. The RF input is directly related to
AD8332Built-in dual, low-noise preamplifier outputs for interface.
A divide-by-four circuit generates the internal 0° and 90° phases of the local oscillator (LO) to drive a pair of mixers matching the I/Q demodulator.
The AD8333 can be used as the primary component of analog beamforming circuitry in medical ultrasound equipment.
The AD8333 has an asynchronous reset pin. When used in array, this reset pin sets all LO dividers to the same state. Each channel can independently select 16 discrete phase rotations in 22.5° increments. For example, if Channel 1 is used as the reference channel and the I/Q phase of the RF signal applied to Channel 2 is 45° ahead, Channel 2 and Channel 1 can be phase-aligned by selecting the correct code.
The phase shift is determined by the output of one channel relative to the other channel. For example, if the code for channel 1 is adjusted to 0000 and the code for channel 2 is adjusted to 0001, and the same signal is applied to the RF input of both channels, the output of channel 2 will be 22.5° ahead of the output of channel 1.
Both the I and Q outputs are supplied in current for easy summing. The summed current output is converted to voltage by a high dynamic range, current-to-voltage (I-V) converter configured as a transimpedance amplifier, such as the AD8021. The resulting signal is then applied to a high resolution ADC such as the AD7665 (16 bits/570 kSPS).
In other nonbeamforming applications, the two I/Q demodulators can be used independently. In this case, each I and Q output requires a transimpedance amplifier, and a total of four transimpedance amplifiers are required for the dual I/Q demodulator.
Each I and Q output has a dynamic range of 159 dB/Hz, but to maintain the full dynamic range, the post-mounted transimpedance amplifier is important, and care should be taken to optimize device selection and design.
The AD8333 is available in a 32-lead LFCSP (5 mm × 5 mm) package and is specified over the industrial temperature range of −40°C to +85°C.
Protected by U.S. Patent No. 7,760,833.
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Medical imaging (CW ultrasonic beamforming)
Phased array systems (radar and adaptive antennas)
Communication receiver