Switching PS
The switching PS rectifies and filters the ac (as the linear PS does), but without using a transformer for lowering the (110 or 220)V, and then converts it into pulses and filters this signal. This switching PS mainly supplies the +5V, used in the CPU. This PS has a better performance than the linear PS. It offers better quality of dc output and is more efficient. Switching PS may use a power transistor or another power device to output as the linear PS does, but they don´t work all the time, instead they work in a cut and saturation way (on-off), so the power consumption is lower because in the off cycle there is no energy consumption, the output of the transistor is rectified and filter again, the (on-off) state has a frequency of several KHz, on account of this frequency (higher than the 60 or 50 cycles used in the linear PS.) the gaps between the rectified positive waves the capacitors have to fill is smaller, so the filtering action offers a very low ripple and a better quality of DC.
CPU
The CPU is the one which controls the tasks of the blocks, and the principal device of this block is the microprocessor, also there are other microprocessors on some blocks which control specific internal tasks of the block.
PROBE SELECTOR
This consists of one or more connector circuitry, HVS, and a control circuit.
Connector board:
For each connector board there are lines in bus connections corresponding to the maximum crystals in the probe. The connector board consists of:
Probe connector:
Is a mechanic device (receptacle) to connect the probe plug.
Relays:
It consists of a large number (more than one hundred) for switching on/off the probe connection
Probe code interface:
Probe code: Every probe model has its own code; and each model has its own properties which are different from each other like the focus during the transmission and reception, the frequency of transmission and reception, Doppler capability, continuous or pulsed, or both of them, etc. When a probe is selected it sends it´s code to the probe code interface. The probe code interface detects the probe code, controls the relay circuit, and outputs the probe code to the data bus, and then the CPU identifies the probe code and offers all the necessary data regarding the probe selected for it to run properly.
HVS:
This has a large number of (HVS) (more than twenty) that selects the Tx/Rx channels out according to the maximum number of crystals in the probe.
HVSC:
This controls the (HVS), by means of ROM and logical circuits.
TRANSMISSION:
Focus calculator:
The image ultrasound process begins with the pulse generation needed to excite the probe crystals, and those crystals will generate the ultrasound lines that travel inside the human body [2]. The transmission signal is not always the same, it changes for each probe, and even using the same probe, some parameters change, that´s why the transmission must be controlled by a TX control to control all the parameters that shape the transmitted signal, one of these parameter is the focus in transmission, the focal point is the convergence point of all the transmitted lines sent from the crystals of the probe in each transmission pulse to form a main ultrasound line shown in figure 2 [2]. The focal point create a focal zone, seen in figure 3, this zone has a better resolution than its rear and forward zones, and as the resolution is better also the image quality is belter too.