Service manual

26 Chapter 4: System Overview
Front End Overview
The Front End is designed to support various imaging modalities such as 2D, M-Mode, Spectral Doppler and Color
Doppler. From the Front End's perspective, all modes can be grouped into a few basic types: Single mode,
simultaneous modes and triggered modes. All these modes are built from similar, basic transmit and receive
sequences controlled within the Front End. A generic top level block diagram of a typical Front End is in the figure
below.
Figure 4.2 Front End Block Diagram
The transmit section consists of a waveform generator, delay block, and high power high voltage driver to excite
the transducer element. Multiple elements are driven with delays determined by the time of flight in the medium
from the elements to the point in space where the beam is to be focused. The longer the time of flight is to the focal
point the smaller the delay is for a given transmit element to allow all to arrive at the focal point at the same time.
Continuous Wave
Doppler Audio
Output
The system provides for audio output of the CW velocity information. This can be
presented as stereo information, with flow moving towards the transducer on one
channel and flow away on the other, or as a mono output with the single audio
output representing the summation of the flow directions.
Pulsed Wave Doppler
Audio Output
The system provides for audio output of the PW velocity information. This can be
presented as stereo information, with flow moving towards the transducer on one
channel and flow away on the other, or as a mono output with the single audio
output representing the summation of the flow directions.
Electrocardiograph
(ECG) Display
ECG is provided to measure the electrical signal generated by the heart. A three lead
interface: Right Arm (RA), Left Arm (LA) and Left Leg (LL), is provided on the system.
The ECG signal is displayed as an amplitude-versus-time sweeping output.
Amplitude is presented on the vertical axis with time along the horizontal axis.
Receive Section
X
T/R Sw
TGC Amplifier
A/D Delay
Weight
Pulser
Waveform
Delay
X
T/R Sw
TGC Amplifier
A/D Delay
Weight
Pulser
Waveform
Delay
Beamformed
Data
Transducer
Transmit Section
Control