Page 1199 - The Mechatronics Handbook

front panel
display and switches
application probe
and transducer
intermodule bus
digital module RF module

power supply/
battery pack

FIGURE 47.1 Basic block diagram of the therapeutic ultrasound unit discussed as an example.

modulator AGC amplifier power amplifier transducer

sinewave
oscillator
AGC

RF-voltage pickoff
and peak detector
integrator
frequency
counter feedback amplifier
and sample/hold

desired + –
power
(reference)

FIGURE 47.2 Simplified block diagram of the RF module used in the ultrasound unit of Fig. 47.1.

The particular unit being discussed consists of five principal subsystems:
1. An application probe and ultrasound transducer, which imparts ultrasonic energy to the tissue
being treated. Note that this transducer is NOT an input transducer such as has been discussed in
relation to signal conditioners.
2. A radio-frequency (RF) module, which provides electrical excitation to the ultrasound transducer.
3. Front-panel display and switches, which allow communication between the unit and its operator.
4. A microprocessor-based digital module, which orchestrates the overall control of the ultrasound
unit.
5. A power supply/battery pack, which provides operating power to the unit.
We focus now on the RF module, whose basic block diagram is shown in Fig. 47.2. The module consists
of a sine-wave oscillator that produces a signal at the resonant frequency of the transducer, a modulator
that allows that signal to be pulse-modulated, and an amplifier with RF-voltage feedback. Incorporated
in the amplifier are a power amplifier capable of driving the transducer and automatic-gain-control (AGC)
circuitry required to adjust the output power to coincide with that selected by the operator. The AGC uses

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