AFE5804 datasheet(46/60 Pages) TI

46 / 60 page

THEORY OF OPERATION

LNA

V/I

CWSwitchMatrix

Attenuator

(VCA)

PGA

Clamp

LPF

CW/I

OUT

T/R

Switch

CNTL

AFE5804

LVDS

Serializer

12-Bit

ADC

AFE5804

SBOS442A – JUNE 2008 – REVISED SEPTEMBER 2008 ................................................................................................................................................ www.ti.com

of 0V to 1.2V. While the LNA is designed to be driven

The AFE5804 is an eight-channel, fully integrated

from a single-ended source, the internal TGC signal

analog

front-end

device.

Its

integrated

LNA,

path is designed to be fully differential to maximize

attenuator, PGA, LPF, and ADC implement a number

dynamic

range

while

also

optimizing

for

low,

of proprietary circuit design techniques to specifically

even-order harmonic distortion.

address

the

performance

demands

medical

ultrasound systems. It offers unparalleled low-noise

CW doppler signal processing is facilitated by routing

and low-power performance at a high level of

the differential LNA outputs to V/I amplifier stages.

integration. For the TGC signal path, each channel

The resulting signal currents of each channel then

consists of a 20dB fixed-gain low-noise amplifier

connect to an 8×10 switch matrix that is controlled

(LNA), a linear-in-dB voltage-controlled attenuator

through the serial interface and a corresponding

(VCA), and a programmable gain amplifier (PGA), as

well as a clamping and low-pass filter stage.

passive delay line that allows coherent summing

Digitally-controlled through the logic interface, the

(beam forming) of the active channels and additional

PGA gain can be set to four different settings: 20dB,

off-chip signal processing, as shown in Figure 95.

25dB, 27dB, and 30dB. At its highest setting, the total

Applications that do not utilize the CW path can

available gain of the AFE5804 is therefore 50dB. To

simply operate the AFE5804 in TGC mode. In this

facilitate

the

logarithmic

time-gain

compensation

mode, the CW blocks (V/I amplifiers and switch

required for ultrasound systems, the VCA is designed

matrix) remain powered down, and the CW outputs

to provide a 46dB attenuation range. Here, all

can be left unconnected.

channels

are

simultaneously

controlled

externally-applied control voltage (VCNTL) in the range

Figure 95. Functional Block Diagram

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