Chapter 5. Product Structure 5 - 17
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 nose 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 Beam forming 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, the VSCG (Variable
Sampling Clock Generator) is necessary. The VSCG (Variable Sampling Clock Generator)
uses 61.6Mhz, which is same as the A/D Sampling Clock; necessary data is generated
within BF ASIC (MCB124A).
To Next Page
Loading...