AD9271 datasheet(24/58 Pages) AD

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AD9271

Preliminary Technical Data

Rev. PrA | Page 24 of 58

typical array sizes of 16 or 32 receiver channels phase-shifted

and summed together to extract coherent information. When

used in multiples, the desired signals from each of the channels

can be summed to yield a larger signal (increased by a factor N,

where N is the number of channels), and the noise is increased by

the square root of the number of channels. This technique

enhances the signal-to-noise performance of the machine. The

critical elements in a beam-former design are the means to

align the incoming signals in the time domain and the means to

sum the individual signals into a composite whole.

Beam forming, as applied to medical ultrasound, is defined as the

phase alignment and summation of signals that are generated

from a common source but received at different times by a

multielement ultrasound transducer. Beam forming has two

functions: It imparts directivity to the transducer, enhancing its

gain, and it defines a focal point within the body from which the

location of the returning echo is derived.

The AD9271 includes the front-end components needed to

implement analog beam forming for CW Doppler operation.

These components allow CW channels with similar phases to be

coherently combined before phase alignment and down mixing,

thus reducing the number of delay lines or adjustable phase

shifters/down mixers (AD8333 or AD8339) required. Next, if

delay lines are used, the phase alignment is performed and then

the channels are coherently summed and down converted by a

dynamic range I/Q demodulator. Alternatively, if phase shifters/

down mixers, such as the AD8333 and AD8339, are used, phase

alignment and down conversion are done before coherently

summing all channels into I/Q signals. In either case, the resultant I

and Q signals are filtered and sampled by two high resolution

ADCs, and the sampled signals are processed to extract the

relevant Doppler information.

AD9271

LNA

SWITCH

ARRAY

8 × AD9271

8 × CHANNEL

16-BIT

ADC

OPA

LNA

AD9271

LNA

SWITCH

ARRAY

8 × CHANNEL

LNA

3 × AD8333

2.5V

AD8333

2.5V

AD8333

16-BIT

ADC

OPA

600nH

700Ω

600nH

Figure 40. Typical CW Doppler System Using the AD9271 and AD8339

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