JPH0248255B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to improvements in ultrasonic diagnostic equipment.

[Technical background of the invention]

Ultrasonic diagnostic equipment uses an ultrasound transducer (hereinafter referred to as "ultrasonic transducer") that emits ultrasound waves using electrical excitation signals to obtain ultrasound image information, and receives reflected waves from the subject to obtain electrical reception signals. (referred to as a vibrator) is used.

FIG. 1 shows the connection relationship between the transducer and the transmitting circuit that drives it in the ultrasonic diagnostic apparatus, where 1 is the transmitting circuit, 2 is the transducer, and 3 is the transmitting circuit 1 and the transducer 2. A cable for electrical connection. In FIG. 1, the transmitting circuit 1 employs a resonant drive method or a non-resonant drive method depending on the impedance relationship between the transducer 3 and the cable at the frequency used, and the transducer 3 efficiently emits ultrasonic waves. This is to prevent the characteristics such as S/N (signal-to-noise ratio) of the reflected wave received by the vibrator 3 from deteriorating. In this case, since the impedance of the cable 2 is mostly a stray capacitance component, it is equivalent to connecting a capacitor 4 in parallel to the vibrator 3, and the vibrator 3 is equivalent to a series circuit consisting of a resistor 5 and a capacitor 6. , FIG. 1 can be represented by an equivalent circuit as shown in FIG.

In the above, when the impedance Z ₁ of the vibrator 3 is larger than the impedance Z ₂ of the cable 2 (Z ₁ >Z ₂ ), a resonance drive method is adopted in which the stray capacitance component of the cable 2, that is, the capacitor 4 resonates. In this resonance drive method, since the transducer 3 is driven by resonance, it is possible to efficiently obtain high-output ultrasonic waves and to transmit and receive ultrasonic waves with a good S/N ratio. The frequency band becomes narrower.

On the other hand, if the impedance Z ₁ of the vibrator 3 is smaller than the impedance Z ₂ of the cable 2 (Z ₁ <
Z ₂ ) adopts a non-resonant drive method. In this non-resonant drive method, the vibrator 3 is excited without using resonance, so the vibrator 3 emits ultrasonic waves having frequency components in a wide band, unlike in the case of a resonant drive method in which the vibration frequency is limited to the resonance frequency. Ru.

Therefore, in an ultrasonic diagnostic apparatus that uses a plurality of types of transducers 3 selectively, a transmitting circuit that can be used regardless of the impedance of the transducers 3 is desired.

FIG. 3 shows a conventional example of the above-mentioned transmitting circuit. For non-resonant drive, power supply voltage +V
is applied to the capacitor 7 via the resistor 8, this capacitor 7 is charged, and the switch 9 is closed, so that the fall is steep and the rise is exponential as shown in FIG. A pulse waveform that rises is generated, and this pulse waveform is applied to the vibrator 3 to drive the vibrator 3.

In addition, in the case of resonance drive, in Fig. 3,
By inserting a coil 11 in parallel with the resistor 10, a resonant circuit is formed, and the resonance generates a waveform whose amplitude gradually attenuates as time passes, as shown in FIG. 3 to drive the vibrator 3.

[Problems with background technology]

Incidentally, in the transmitting circuit 1 shown in FIG. 3, it is possible to perform resonant driving and non-resonant driving, but the excitation waveform during non-resonant driving is as shown in FIG. 4a. In other words, this waveform closes the switch 9, so the fall is steep (the time required for the fall is
t ₁ ), but since the cable 2 and vibrator 3, which are loads for the transmitting circuit 1, are capacitive, the rise rises exponentially (time required from rise to fall; excitation time). t ₂ ).
For this reason, the frequency spectrum of the pulse waveform for non-resonant driving becomes downwardly convex as shown in FIG. 5, so that the higher the frequency, the lower the output. In addition, the waveform during non-resonant driving has an exponential rise as shown in Figure 4a, so the excitation time _t2 is much longer than the fall time _t1 . . However, when trying to perform burst drive in which the vibrator 3 is excited by a continuous excitation pulse train, which is used when measuring the flow of blood in the heart or the like using the Doppler effect, for example, the method shown in FIG. Using the waveform shown, the period t ₃ of burst drive cannot be made very short. This is because if this period t ₃ becomes shorter than the excitation time t ₂ , the excitation pulse trains will overlap with each other. Therefore, in this case, there was a problem that high frequency burst driving was not possible.

[Purpose of the invention]

The present invention was made based on the above circumstances, and
The purpose is to provide an ultrasonic diagnostic apparatus capable of wide-band drive and high-frequency burst drive during non-resonant drive.

[Summary of the invention]

The present invention provides an excitation signal for exciting a transducer from a transmission circuit to the transducer via a cable, transmits ultrasonic waves to a subject, receives reflected waves with the transducer, and generates an electrical reception signal. In the ultrasonic diagnostic apparatus that obtains ultrasonic image information by using
a first MOS between the power supply and the cable;
a first switching circuit comprising a FET, a first diode forward biased with respect to the power supply connected in series to the drain or source of the FET, and one end of a capacitor connected to the gate; and a stray capacitance of the cable. A second diode that is forward biased with respect to the charge accumulated in the resonator between the two ends, and a second MOS FET in series with the second diode, which opens and closes the parallel circuit of the resonator and the resonator. a second switching circuit having a gate connected to the other end of the capacitor;
and a drive circuit that alternately opens and closes a second switching circuit, and outputs a drive signal to each gate of the first MOS FET and the second MOS FET complementary thereto. It is characterized by having the following.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In FIG. 7, 12 is a drive circuit that outputs, for example, a rectangular waveform drive signal A shown in FIG. 8 from output terminals X and Y. One output terminal X of this drive circuit 12 is an N-channel power MOS
FET (metal oxide field effect transistor for power use;
(hereinafter abbreviated as FET) is connected to the gate of 13. Further, the output terminal X is connected to the gate of the P-channel type FET 14 via a capacitor 15 whose one end is connected to the gate of the P-channel type FET 14. The other output terminal Y of the drive circuit 12 is grounded and connected to the source of the FET 13. A resistor 16 is connected between the output terminals X and Y of the drive circuit 12.

On the other hand, a resistor 17 is connected between the gate and source of the FET 14, and the source is connected to the power supply voltage +
V ₀ is applied. Further, the drain of FET 14 is connected to the anode of diode 18, the cathode of diode 18 is connected to the anode of diode 19, and the cathode of diode 19 is connected to the drain of FET 13. Therefore, in the above, the N-channel type FET 13 and the P-channel type FET 14 constitute a complementary circuit, and the FETs 13 and 14 are alternately driven on and off by the drive signal A of the drive circuit 12. In the above, the FET 14, the capacitor 15, the resistor 17, and the diode 18 constitute a first switching circuit, and the FET 13, the resistor 16, and the diode 19 constitute a second switching circuit. One output terminal M of the transmitting circuit is derived from the connection point between the diode 18 and the diode 19, and the other output terminal N of the transmitting circuit is derived from the source of the FET 13. Further, a series circuit of a switch 20 and a coil 21 is connected between output ends M and N of this transmitting circuit for resonance driving. Further, a vibrator 3 is connected to output ends M and N of the transmitting circuit via a cable 2 having a capacitor 4 as a stray capacitance.

Next, the operation of this embodiment configured as described above will be described. First, we will discuss non-resonant drive.
That is, when _the drive circuit 12 outputs _the rectangular waveform drive signal _A shown in _FIG . , FET13 is turned off and FET14 is turned on.

Therefore, if the forward voltage drop due to FET 14 and diode 18 is ignored, the power supply voltage V ₀ is
The signal is outputted to the output terminals M and N of the transmitting circuit via the FET 14 and the diode 18. That is, the transmission signal B in FIG. 8 has a voltage V ₀ in the section K ₁ . next,
In the high level voltage _V2 section _K2 of the drive circuit 12 output,
FET13 is turned on and FET14 is turned off.
Therefore, no voltage appears at the output terminals M and N of the transmitting circuit, and the charges stored in the capacitor 4 and the vibrator 3, which are the stray capacitance of the cable 2, are discharged through the second switching circuit that is in the on state. be done. That is, the transmission signal B in FIG. 8 has a voltage of zero in section _K2 . Furthermore, in section _K3 , since the drive signal A is at the low level voltage _V1 , the transmission signal B is at the power supply voltage _V0.
is output. According to the above, during non-resonant driving,
It becomes possible to output the rectangular wave transmission signal B. In addition, the frequency spectrum of the rectangular wave as shown in Figure 9a is upwardly convex as shown in Figure 9b, so the conventional waveform as shown in Figure 4a (the frequency spectrum is shown in Figure 5). ), the decrease in ultrasonic output is small even in the high frequency range, making it applicable over a wide frequency band. Furthermore, the diode 18 is in a forward bias state (on operation) when the first switching circuit is in operation, and the charge accumulated in the transducer 3 when the first switching circuit is not in operation is transferred to the transducer 3 when the reflected ultrasound is received. It turns off in response to received signals. This results in
To prevent malfunction of the FET 14 without applying unnecessary charge or voltage to the drain of the FET 14.

Furthermore, the diode 19 is in a forward bias state when the second switching circuit is in operation, and discharges the charge accumulated in the vibrator 3, and when the second switching circuit is not in operation, the electric charge accumulated in the vibrator 3 is transferred to the vibrator 3 during reception. Do not apply the received signal directly to the drain of FET13. That is, since the received signal is normally several hundred mV and the barrier voltage of the diodes 18 and 19 is usually around 0.6V, the diode 19 will not turn on. Temporarily diode 19
When turned on, the signal received by the vibrator 3 is grounded. Therefore, according to this embodiment, the reliability of the transmitting circuit can be improved without causing the FETs 13 and 14 to malfunction, and the received signal can be efficiently obtained.

Furthermore, it is possible to make the drive signal A from the drive circuit 12 into a rectangular wave with a pulse width shorter than 1/2 cycle of the unique frequency of the vibrator 3, and the frequency component having this rectangular wave is the frequency component of the vibrator 3. Since the frequency components are covered over the entire range, it is possible to use a wide range of frequencies in ultrasonic diagnosis.

Further, since the transmission signal B is a rectangular wave and the pulse width can be narrowed, it is possible to output continuously so that the excitation waveforms do not overlap each other, and high-frequency burst driving can be performed.

In addition, during the above-mentioned burst drive, for the amplitude H of one rectangular wave shown in FIG. 9a for ₁ time T ₁ , the 10
By continuously outputting a pulse with the amplitude H ₂ (H ₁ > H ₂ ) and time T ₂ (T ₁ > T ₂ ) shown in Figure 10 (a), the frequency spectrum of the waveform in Figure 10 (a) is shown in Figure 10 (b).
It is possible to make the signal output in FIG. 9a and the signal output in FIG. 10a the same excitation energy near the natural frequency of the vibrator 3, and therefore FET13,
14 can be used with a low withstand voltage that switches low voltage, making it possible to reduce costs.

On the other hand, when performing resonance drive, switch 20
is closed, and the coil 21 is connected to the output terminals M and N of the transmitting circuit. As a result, coil 21 and capacitor 4
and form a resonant circuit. The drive circuit 12 sends a drive signal A of low level voltage _V1 to the first and second
switching circuit. This allows the first
The second switching circuit is turned on and the second switching circuit is turned off, and an excitation signal is applied to the vibrator 3 by the resonant circuit formed by the capacitor 4 and the coil 21, so that the vibrator 3 is driven resonantly.

In this embodiment, in order to obtain a switching function in a high frequency band in the first and second switching circuits, complementary configuration MOS FETs 13,
14 is used, but the present invention is not limited to the above-mentioned elements, and other elements and circuits having the same function as the above-mentioned elements may be used. In addition to this, the present invention can be implemented with various modifications without changing the gist.

〔Effect of the invention〕

According to the present invention described above, during non-resonant driving,
Since a high frequency rectangular wave excitation signal can be obtained, the transducer can be used in a wide range of frequencies, and high frequency burst driving is also possible, making it possible to provide an ultrasonic diagnostic device that can improve the reliability of the transmitter circuit. .

[Brief explanation of the drawing]

Figure 1 is a diagram showing the connection relationship between the transmission circuit, cable, and vibrator in an ultrasound diagnostic device, Figure 2 is an electrical equivalent circuit diagram of Figure 1, and Figure 3 is the main part of a conventional ultrasound diagnostic device. Figures 4a and 4b are waveform diagrams of excitation signals, Figure 5 is the frequency spectrum of the waveform shown in Figure 4a, and Figure 6 is for explaining problems during conventional burst drive. FIG. 7 is a circuit diagram showing an embodiment of the present invention, FIG. 8 is a waveform diagram for explaining the operation of the same embodiment, FIG. 9a, FIG. 10a, and FIG. 9b , FIG. 10b are a waveform diagram and a frequency spectrum, respectively, for explaining the operation of the same embodiment. 2... Cable, 3... Vibrator, 4... Capacitor, 5... Resistor, 6... Capacitor, 12...
Drive circuit, 13...N-channel type power
MOS FET, 14...P channel type power
MOS FET, 15... Capacitor, 16, 17
...Resistor, 18,19...Diode, 20...
Switch, 21...Coil.

Claims (1)

[Claims] 1. An excitation signal that excites the transducer is applied from a transmission circuit to the transducer via a cable to transmit ultrasonic waves to the subject, and the reflected waves are received by the transducer to obtain an electrical reception signal. In the ultrasonic diagnostic apparatus for obtaining ultrasonic image information, the transmitting circuit opens and closes between the power source and the cable, and includes a first MOS FET and its drain between the power source and the cable. Alternatively, a first switching circuit comprising a first diode in a forward bias state with respect to the power source connected in series with the source and one end of the capacitor connected to the gate, and the stray capacitance of the cable and the resonator. A device that opens and closes both ends of a parallel circuit, wherein a second diode that is forward biased with respect to the charge accumulated in the vibrator is connected between the two ends, and a second MOS FET connected in series with the second diode. A second switching circuit whose gate is connected to the other end of the capacitor, and the first and second switching circuits are alternately opened and closed, and the first MOS FET and the second switching circuit are connected to each other. An ultrasonic diagnostic apparatus comprising: a drive circuit that outputs a drive signal to each gate of the complementary second MOS FET.