Communications – electrical: acoustic wave systems and devices – Transmitter systems
Patent
1980-04-14
1982-08-31
Farley, Richard A.
Communications, electrical: acoustic wave systems and devices
Transmitter systems
367138, G01S 752, G01K 1100
Patent
active
043475922
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an arrangement for generating amplitude-modulated, ultrasonic transmission pulses. An arrangement of this type is used preferably for generating transmission pulses with a small frequency spectrum and, in particular, with a low side-lobe level in order to achieve better detection of doppler-shifted echo signals.
Such an arrangement is known in an embodiment comprising a linear amplifier, connected to a high-power, fixed-frequency oscillator and driven with a control voltage of a suitably selected amplitude behaviour to obtain amplitude modulation of the oscillator output voltage. This arrangement has the disadvantage that it becomes complicated and costly if it is required to generate high power, ultrasonic transmission pulses in accordance with a predetermined amplitude behaviour with sufficient accuracy.
SUMMARY OF THE INVENTION
It is an object of the present invention, therefore, to provide an arrangement as set forth in the opening paragraph, whereby the above disadvantage is substantially obviated.
According to the invention, the arrangement for generating amplitude-modulated, ultrasonic transmission pulses comprises a combination of:
a. a switching circuit controlled with a plurality of switching pulses per pulse interval, which switching circuit includes an inductive load circuit for generating the transmission pulses;
b. a unit for generating timing signals determining the switching pulse frequency;
c. a memory, of which the memory locations are filled with the information, required per transmission pulse interval, about the pulse width of the switching pulses to be generated, which information is derived from the desired amplitude pattern of the transmission pulses to be generated;
d. a switching-pulse generator for producing the switching pulses, using the timing signals on the one hand and the pulse width information in the memory on the other hand;
e. an address generator for generating addresses on the supply of the timing signals to read out the memory.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described with reference to the accompanying five figures of which:
FIG. 1A is a timing diagram of a limited number of pulsed signals of varying width to obtain an amplitude-modulated ultrasonic transmission pulse, while
FIG. 1B is a fragment of the timing diagram of FIG. 1A;
FIG. 2 is a timing diagram of an ultrasonic transmission pulse, whose amplitude is governed by the pulsed signals shown in FIG. 1A;
FIG. 3 is a block diagram of an arrangement for generating amplitude-modulated ultrasonic transmission pulses according to the invention;
FIGS. 4A-G are a number of timing diagrams for illustrating the active state of various units forming part of the switching-pulse generator to obtain switching pulses for the switching circuit; and
FIG. 5 is a block diagram of a combination of arrangements for generating amplitude-modulated ultrasonic transmission pulses according to the invention to obtain a transmission pulse having a defined wavefront.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The timing diagram of FIG. 1A shows a sequence of pulsed signals generated at a given frequency f.sub.p, while each pair of pulses has the same pulse width with an alternating polarity. Apart from such a pulse width behaviour, the pulse width increases in time to a given value and subsequently decreases. When a sequence of signals of this sort is applied to an inductive load circuit of suitable dimensions, it will produce as signal component the first harmonic of this sequence, the characteristics of which harmonic being illustrated in FIG. 2. This figure shows an amplitude-modulated signal, of which the frequency f.sub.w, being also the transmitting frequency, is given by the relationship: f.sub.w =1/2f.sub.p. The amplitude of this signal depends on the pulse width of the pulsed signal in relation therewith and can be calculated by the Fourier method of analysis. For a desired amplitude behaviour of the abovementioned signal component it is thus
REFERENCES:
patent: 3243728 (1966-03-01), Brainerd et al.
patent: 3806862 (1974-04-01), Chao
Farley Richard A.
Hollandse Signaalapparaten B.V.
Kraus Robert J.
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