AD8335 datasheet(20/24 Pages) AD

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AD8335

Rev. 0 | Page 20 of 24

APPLICATIONS

ULTRASOUND

The primary application for the AD8335 is medical ultrasound.

Figure 57 shows a simplified block diagram of an ultrasound

system. The most critical function of an ultrasound system is

the time gain control (TGC) compensation for physiological

signal attenuation. Because the attenuation of ultrasound signals

is exponential with respect to distance (time), a linear-in-dB

VGA is the optimal solution.

Key requirements in an ultrasound signal chain are very low

noise, active input termination, fast overload recovery, low

power, and differential drive to an ADC. Because ultrasound

machines use beamforming techniques requiring large binary

weighted numbers (for example, 32 to 512) of channels, the

lowest power at the lowest possible noise is of key importance.

Most modern machines use digital beamforming. In this

technique, the signal is converted to digital format immediately

following the TGC amplifier; beamforming is done digitally.

Typical ADC resolution in general purpose machines is 10 bits

with sampling rates greater than 40 MSPS, while high end

systems use 12 bits.

Power consumption and low cost are of primary importance in

low-end and portable ultrasound machines, and the AD8335 is

designed for these criteria.

For additional information regarding ultrasound systems, refer

to “How Ultrasound System Considerations Influence Front-

End Component Choice”, Analog Dialogue, Vol. 36, No. 3,

May–July 2003.

(http://www.analog.com/library/analogDialogue/archives/36-

03/ultrasound/index.html)

BEAMFORMER

CENTRAL CONTROL

Rx BEAMFORMER

(B AND F MODES)

COLOR

DOPPLER (PW)

PROCESSING

(F MODE)

IMAGE AND

MOTION

PROCESSING

(B MODE)

SPECTRAL

DOPPLER

PROCESSING

MODE

DISPLAY

AUDIO

OUTPUT

TX BEAMFORMER

CW (ANALOG)

BEAMFORMER

LNAs

TRANSDUCER

ARRAY

128, 256 ETC.

ELEMENTS

BIDIRECTIONAL

CABLE

MUX/

DEMUX

T/R

SWITCHES

TX HV AMPs

MULTICHANNEL

TGC USES MANY VGAs

TGC

TIME GAIN COMPENSATION

VGAs

AD8335

Figure 57. Simplified Ultrasound System Block Diagram

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