Datasheet

C
IN
LNA
V/I
CWSwitchMatrix
Attenuator
(VCA)
PGA
Clamp
LPF
CW/I
OUT
OUT
OUT
T/R
Switch
V
CNTL
AFE5805
LVDS
Serializer
12-Bit
ADC
AFE5805
www.ti.com SBOS421D –MARCH 2008–REVISED MARCH 2010
THEORY OF OPERATION
of 0V to 1.2V. While the LNA is designed to be driven
The AFE5805 is an 8-channel, fully integrated analog
from a single-ended source, the internal TGC signal
front-end device controlling the LNA, attenuator,
path is designed to be fully differential to maximize
PGA, LPF, and ADC, that implements a number of
dynamic range while also optimizing for low,
proprietary circuit design techniques to specifically
even-order harmonic distortion.
address the performance demands of 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 register. The CW outputs are typically routed to a
well as a clamping and low-pass filter stage. Digitally passive delay line that allows coherent summing
controlled through the logic interface, the PGA gain (beam forming) of the active channels and additional
can be set to four different settings: 20dB, 25dB, off-chip signal processing, as shown in Figure 46.
27dB, and 30dB. At its highest setting, the total
Applications that do not utilize the CW path can
available gain of the AFE5805 is therefore 50dB. To
simply operate the AFE5805 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 by an
externally-applied control voltage (V
CNTL
) in the range
Figure 46. Functional Block Diagram
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