5 - 18 WS80A Service Manual
are sent to the Pre-Amp. The Limiter removes signal over approximately 0.6V before
sending the echo signal to the Pre-Amp.
2) Pre-Amp
The Pre-Amp amplifies the unprocessed small-magnitude echo signal in mV range.
3) TGC-Amp
The TGC (Time Gain Compensation) Amp consists of 4 channels per one unit.
It compensates for the time or distance-dependent reduction characteristics of echo
signals that have been propagated through, or reflected from, media
4) Anti-aliasing Filter (Low Pass Filter)
The Low-Pass Filter filters the noise out of Stop Band, which is not the band of ultrasound
signals. It also serves as an anti-aliasing filter, minimizing the aliasing phenomena that
may occur with high frequency probes such as the 7.5MHz probe. Aliasing phenomena of
high-frequency probes are caused by the restriction of the sampling clock in BF ASIC.
5) A/D Converter
This converts an analog signal into a digital signal to be used for Digital Beamforming.
Digital Beam forming
Ultrasonic waves generated by a probe use a Channel method that utilizes multiple
Elements to perform TX Focusing. Ultrasonic waves generated from each channel are
reflected by media and return as reflected echo signals. However, the echoes do not
return to the Probe Element simultaneously; they return to each Element at different times,
which necessitates a way to compensate for this time difference. It is required to perform
RX Focusing; it is also very important for generating ultrasound images.
Digital Beamforming takes the echo signals entering the Probe Element and samples the
data at the junction of the time axis and the curve, which is then stored in the memory.
When sampling is complete, the data accumulated in the memory have been time-
compensated when they were stored; time compensation is performed by the Sampling
Clock itself. RX Focusing is completed by simply reading the data stored in the memory
and adding them. Since this method requires different Sampling Clocks for each Element,
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