JPH0774608A - Switch circuit and ultrasonic diagnostic system using same - Google Patents

Abstract

PURPOSE:To attain the fast switching actions of a switch circuit with small electric power by providing such a circuit that drives early an LED of an optical coupler with large current of a constant level and then with small current of a constant level after a switch is turned on respectively. CONSTITUTION:Each of drive circuits 141, 142...14m of high analog switches consists of the resistances R1 and R2 connected to an LED 8, the FET 15 and 16 serving as the switching elements that control the currents flowing to both R1 and R2, and a monostable multivibrator MM17. When a signal is applied to the signal input terminal of one of circuits 141-14m that should be closed, the MM17 is triggered by the rise of the signal and the pulse signals are transmitted for a fixed time. Therefore the FET 25 conducts and a large current decided by the R1 flows for a fixed time. As a result, the FET 7a and 7b serving as analog switches are turned on. The fixed time means a time during which both FET 7a and 7b are turned on.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switch circuit for switching connection between a transducer element, a transmission pulse generator and a receiver in an ultrasonic diagnostic apparatus, and an ultrasonic diagnostic apparatus using the switch circuit. is there.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional intelligent sound wave diagnostic apparatus has a plurality of transducer elements 1 ₁ , 1 ₂ ,
...... A probe 2 for transmitting and receiving ultrasonic waves by arranging 1 _m adjacent to each other on the sound absorbing material, and each transducer element 1 ₁ in the probe 2
~ 1 _n is given a predetermined delay time to apply a driving pulse for ultrasonic ejection to n transmission pulse generators 3 ₁ , 3 ₂ ,
...... 3 _n and a vertical double-diffused field effect transistor (hereinafter abbreviated as VDMOS FET) are connected in anti-series, and high withstand voltage analog switches 4 ₁ , 4 ₂ , ... 4 _n , ...
4 _m , the transducer elements 1 ₁ to 1 _{m of the} probe 2, the transmission pulse generators 3 ₁ , 3 ₂ , ... 3 _n and the receivers 5 ₁ , 5 are used.
₂ , ... Switch connection with 5 _n . A large number of these high withstand voltage analog switches form a changeover switch group 6.

The high withstand voltage analog switch used here has two field effect MOS transistors (MOSFE) as shown by 4 ₁ surrounded by a broken line as 4 in FIG.
T) The potential between the gate and drain of 7a and 7b is supplied by an optical coupling circuit (photocoupler) 10 including a light emitting diode 8 and a photovoltaic diode array 9. Since the vertical MOSFETs 7a and 7b have parasitic diodes 12a and 12b, respectively, two diodes are connected in anti-series as shown in the figure for use as an AC switch. By using the switch circuit having such a configuration, when the control signal is applied to the input terminal, the light emitting diode 8 emits light, and this light enters the photovoltaic diode array 9 to generate a photovoltaic current. , MOSFET 7a and 7b gate capacitance is charged. This charge raises the gate voltage,
Turn on ETs 7a and 7b. Next, when the control signal is removed from the input terminal, the light emission from the light emitting diode 8 is stopped, the charge of the gate is discharged through the resistance 11 of the gate and source of the MOSFETs 7a and 7b, and the MOSFETs 7a and 7b are discharged. Turn off.

When the switch circuit configured as described above is applied to the high voltage analog switch of the changeover switch 6 of the ultrasonic diagnostic apparatus shown in FIG. 3, the control signal circuit and the transducer elements 1 ₁ to 1 of the probe 2 are applied. _{The m} circuit is completely electrically isolated,
This is effective because the fluctuation of the ground potential of the control signal circuit does not cause noise and mix into the circuits of the transducer elements 1 ₁ to 1 _m . Further, when the above switch circuit is used, the magnitude of the potential of the circuit of the transducer elements 1 ₁ to 1 _m depends on the MOSFET 7.
Since there is no influence between the gate and source for turning on and off a and 7b, the MOSFETs 7a and 7a
The on-resistance of b does not change with this circuit potential,
It has a characteristic that waveform distortion is not generated, and it is effective for improving the performance of the ultrasonic diagnostic apparatus.

[0005]

In the analog switch having the structure as shown in the above-mentioned prior art, the switching time for closing the analog switch is determined by the photovoltaic current of the photovoltaic diode array 9 of the photocoupling element 10 and the gate of the FET. Is determined by the time it takes to reach the potential at which the FET is turned on. Here, in order to rapidly charge and raise the gate potential of the FET, the current of the optical coupling element 10 may be increased. FIG. 4 shows the relationship between the forward current I _F and the terminal voltage at the output end in the light emitting diode of the used optical coupling element TLP190B. Here, the larger the load resistance R _SH corresponding to the resistor 11 shown in FIG. 3, the larger the terminal voltage. When the terminal voltage value is large, when the operation of opening the FET by turning off the current of the light emitting diode is delayed, the charge accumulated in the gate of the FET becomes slow, and the speed at which the FET turns off decreases. However, it is set to an appropriate value.

In order to close the high withstand voltage analog switch at high speed, it is effective to increase the drive current of the optical coupling element, but the power consumption of the element increases. In particular, an ultrasonic diagnostic apparatus using a large number of the above-mentioned switches causes a problem.
For such a problem, a method of driving the optical coupling element 10 by the circuit shown in FIG. 5 has been proposed (Electronics Engineering (Electronics Engineer).
ing) February 1986, p. 84). In the above circuit, the light emitting diode of the optocoupler has a resistance value R ₁ depending on the signal voltage E.
And R ₂ and resistors 11 ′ and 13 ′. A capacitor 12 'is connected in parallel with the resistor 11'.
, A steady current of I _S = E / (R ₁ + R ₂ ) flows, but immediately after the rectangular wave voltage E is applied, the steep charging current to the capacitor 12 ′ instantly causes i
A large current of _p = R / R ₁ flows. Here, the diode 14 'is a bypass circuit for the discharge current of the capacitor 12', and acts so as not to reverse the polarity of the voltage between the light emitting diode terminals of the optical coupling element.

FIG. 6 shows the optical coupling element 10 shown in FIG.
3 shows a typical diode current waveform in the light emitting diode drive circuit of FIG. Immediately after applying a voltage to the optical coupling element 10, a large current of E / R ₁ instantaneously flows. Therefore, in the optical MOSFET switch circuit using the above drive circuit,
The gate of the FET is instantly charged by the photovoltaic current, and then the holding current for keeping the gate constant is supplied, so that the switch can be turned on at high speed and the efficiency of the driving power is improved. . However, in the above drive circuit, the current sharply drops immediately after driving the light emitting diode, and therefore the effect is small in spite of increasing the peak value of the current. Decreasing the value of the resistor 13 'and increasing the peak value is controlled by the current withstand of the light emitting diode. Further, increasing the current is not desirable because it may cause noise in peripheral circuits due to a rise in ground potential. In order to solve the above problems, the current having the waveform as shown in FIG.
It drives the light emitting diode of the optocoupler.

That is, the FE of the optical MOSFET switch
Assuming that the time required to reach the necessary charge Q ₀ in order to charge the T gate and obtain the voltage sufficient to turn on the FET is t ₀ , the charging current i of the FET gate and the charge Q _{0 are given.} The following equation holds between and.

[0009]

[Equation 1]

Current and FE of the light emitting diode of the optical coupling element
Assuming that T and the charging current of the gate of proportional, if the current peak value i _p of the light emitting diodes in the same, and drives the light emitting diode so that the current waveform shown in FIG. 6, FET is The light emitting diode is driven so that the time t _{1 for} turning on and the current having the waveform shown in FIG.
Comparing with the time t ₂ when ET is in the ON state, the charge Q ₀ in the above equation corresponds to the areas S ₁ and S ₂ shown in FIGS. 6 and 7. The above areas S ₁ and S ₂ are naturally S ₁ = S ₂
Therefore, t ₂ <t ₁ , and the FET can be turned on more quickly by driving the light emitting diode so that the current has a waveform as shown in FIG. 7.

It is an object of the present invention to obtain a switch circuit for increasing the switching speed of an optical MOS switch for switching between a transducer element, a transmitter pulse generator and a receiver.

[0012]

The object of the present invention is to provide a switching circuit for operating an analog switch by applying a gate voltage of a field effect transistor by an optical coupling element composed of a light emitting diode and a photovoltaic element. A switching element that keeps the current of the light-emitting diode for turning on the transistor in the constant state for a certain initial period and a gate voltage that keeps the field effect transistor in the on state after the certain period of time. This is achieved by having a switching element that allows a current to flow in and a functional element that imparts the above operation sequence.

That is, the switch circuit supplies the potential between the gate and drain of the FET by means of a photo-coupled device including a light emitting diode and a photovoltaic diode array, and at the same time, switches the light emitting diode from an OFF state to an ON state at high speed. In order to enter the state, the drive current of the light emitting diode is initially driven by a constant large current by a plurality of switches, and when the FET of the changeover switch is in the ON state, it is driven by the small current necessary to maintain the state. To do so.

Further, by using the above switch circuit, a plurality of transducer elements are arranged to transmit and receive ultrasonic waves, and each transducer element in the probe is provided with a predetermined delay time. Switching between the transducer element of the probe and the transmission pulse generator by means of a transmission pulse generator that applies a drive pulse for launching a sound wave and a high-voltage analog switch, and a faster switching operation with less power than before. A small ultrasonic diagnostic apparatus capable of performing the above is obtained.

[0015]

An ultrasonic diagnostic apparatus using a switch circuit according to the present invention includes a probe in which a plurality of transducer elements are arranged to transmit and receive ultrasonic waves, and ultrasonic waves are generated by giving a predetermined delay time to each of the transducer elements. A high-voltage analog switch is used to switch between the transmission pulse generator for applying a pulse for launching a pulse, and a circuit for controlling the analog switch, which is an FET, by an optical coupling element, when the analog switch is turned from the off state to the on state. A circuit for driving the light emitting diode of the optical coupling element with a constant large current at the initial stage and driving with a constant small current when the switch is turned on is provided, and an operation capable of switching at high speed with small power is performed.

FIG. 8 shows the principle of the drive circuit for the light emitting diode. In an optical coupling element 10 composed of a light emitting diode 8 and a photovoltaic diode array 9, resistors R ₁ and R ₂ and switches S ₁ and S ₂ are connected to one end of the light emitting diode 8 as shown in the drawing to emit light. The current of the diode 8 is configured to be supplied from a power source whose voltage is E.
Now, when switches S ₁ and S ₂ are closed, i _p = E / R ₁
Current of magnitude F flows and is connected to the optical coupling element 10
The ET can be turned on at high speed. After that, when only the switch S ₁ is opened, the light emitting diode 8 is i _s = E (R
A small current of ₁ + R ₂ ) can be maintained. The above effect can be obtained by the drive circuit of the light emitting diode 8 provided with the plurality of switches as described above.

[0017]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a main part of an ultrasonic diagnostic apparatus using a switch circuit according to the present invention, and FIG. 2 is a diagram showing the entire configuration of the ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus obtains a tomographic image of a diagnostic region of a subject using ultrasonic waves, and the main part of the ultrasonic diagnostic apparatus using the switch circuit according to the present invention is as shown in FIG. , The probe 2, the transmission pulse generators 3 ₁ , 3 ₂ , ... 3 _n and the receivers 5 ₁ , 5 ₂ ,
... 5 _n and a changeover switch section 6 are provided.

The probe 2 transmits / receives ultrasonic waves to / from a diagnostic region of a subject and has a plurality of transducer elements 1 ₁ , 1 ₂ , ... 1 _m formed in strips, for example. Are arranged in a line adjacent to and above the sound absorbing material. The transmitted pulse generators 3 _{1 to} 3 _n are the transducer elements 1 ₁ to 1 _m in the probe 2.
A predetermined delay time is given to the transducer element selected from, a drive pulse for ultrasonic ejection is applied,
Each of the receivers 5 _{1 to} 5 _n receives an echo signal from the subject and is provided with, for example, n each. The changeover switch unit 6 is a high voltage analog switch 4 ₁ , 4 ₂ , ... 4 _{m formed} by connecting vertical MOSFETs 12 _a and 12 _b in anti-series.
Is used to switch the connection between the transducer elements 1 ₁ to 1 _{m of the} probe 2 and the transmitted pulse generators 3 _{1 to} 3 _n, and control is performed so as to perform electronic linear scanning, for example. Here, in the present invention, the high breakdown voltage analog switches 4 ₁ to 4 _m used as the changeover switch section 6 are configured as shown in the internal circuit diagram of the first high breakdown voltage analog switch noted with reference numeral 4 ₁ . Has been done. Further, the drive circuits 14 ₁ , 1 of the high breakdown voltage analog switch, which is a feature of the present invention,
4 _2, ...... 14 _m has a structure as shown in the drive circuit of the internal circuit 4 ₁ showing by reference numeral 14 _1. The internal structure of the high voltage analog switch used here is
This is the same as the conventional circuit shown in FIG.

Driving circuit 1 for the above-mentioned high voltage analog switch
_{4 1, 14 2, ...... 14} m , the light emitting diode and a resistor R _1, R ₂ connected to 8, FET15,16 as a switching element for controlling a current flowing through these resistors and mono side stable multivibrator ( Hereinafter, abbreviated as MM) 17. Here, if a capacitor 18 is provided in the power source of the voltage E, it is convenient to suppress the voltage fluctuation when an instantaneous large current flows through the light emitting diode 8. When a signal is applied to the signal input terminal of the signal input of the circuit to be closed by the drive circuits 14 _{1 to} 14 _m , the MM 17 is triggered by the rising edge of the signal and a pulse signal is output for a certain time (t ₃ ). It has become. Therefore, the FET 15 becomes conductive, and a large current i = E / R ₁ determined by the resistance R ₁ flows until time t ₃ , and as a result, the FETs 7a and 7b that are analog switches are turned on. Here, the constant time t ₃ is designed to be the time required for the FETs 7a and 7b to reach the ON state. On the other hand, when a signal is applied to the IN terminal shown in the figure, the FET 15
Since the FET 15 is turned off at the same time, the current of the light emitting diode 8 becomes a current i = E / (R ₁ + R ₂ ) of a magnitude determined by the resistors R ₁ and R ₂ . This may be of a size required to maintain the FETs 7a and 7b in the ON state, and is effective in reducing the power for keeping the FETs in the ON state.

The operation when the high withstand voltage analog switch according to the present invention is used as the changeover switch of the ultrasonic diagnostic apparatus is as described above. However, the configuration of the entire ultrasonic diagnostic apparatus using this changeover switch circuit is shown in FIG. 2 shows. In FIG. 2, transmission of a pulse from a transmission pulse generator 3 to a probe 2 in which transducer elements 1 ₁ to 1 _n having a narrow width are arranged in a line and reception of an echo signal based on the transmission pulse. Are selectively switched by the changeover switch unit 6 composed of the high withstand voltage analog switch of the present invention. Each of the received echo signals selectively switched by the change-over switch passes through the amplifier 18 whose gain changes with time, and is then delayed by giving a time delay to each signal so that the directivity of the ultrasonic beam becomes appropriate. After passing through the circuit 19, it is guided to the phasing circuit 21 having a function of adding by the adder 20. The output of the phasing circuit 21 is detected by the detector 22 and displayed on the display device 23 as diagnostic information such as a tomographic image, but the series of operations described above is controlled by the control unit 24 shown in the figure.

[0021]

As described above, in the switch circuit according to the present invention and the ultrasonic diagnostic apparatus using the switch circuit, the gate voltage of the field effect transistor is given by the optical coupling element including the light emitting diode and the photovoltaic element, In a switch circuit that operates an analog switch, a switching element that keeps a current of a light emitting diode for turning on the field effect transistor in a constant state for an initial fixed period, and turns on the field effect transistor after the fixed period. A field effect transistor that operates as a high breakdown voltage analog switch is provided in an optical coupling circuit by including a switching element that allows a current of a magnitude necessary to provide a gate voltage to be maintained and a functional element that imparts the above operation sequence. In addition to controlling, the light emitting diode used in the above optical coupling circuit Using a plurality of switching elements, resistors connected to them, and a monostable multivibrator, a large constant current is passed for a certain period of time after the control signal is applied to the high voltage analog switch, and then its magnitude is changed. The ON state is maintained as a reduced constant current. Therefore, the high withstand voltage analog switch circuit can switch the light emitting diode from the off state to the on state at high speed with low power consumption, and in the ultrasonic diagnostic apparatus using a large number of the switches, the transducer element and the transmission pulse are generated. Although a high-speed switching between the ultrasonic wave receiver and the echo signal receiver can be performed, a high-performance ultrasonic diagnostic apparatus can be obtained which consumes less electric power and is therefore smaller in size and lower in cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of an essential part of an ultrasonic diagnostic apparatus using a switch circuit according to the present invention.

FIG. 2 is a diagram showing the entire configuration of the ultrasonic diagnostic apparatus.

FIG. 3 is a diagram showing a main part of a conventional ultrasonic diagnostic apparatus.

FIG. 4 is a diagram showing a characteristic example of an optical coupling element used in a changeover switch circuit.

FIG. 5 is a diagram showing a drive circuit of a conventional changeover switch.

FIG. 6 is a diagram illustrating characteristics of a conventional drive circuit.

FIG. 7 is a diagram illustrating characteristics of the drive circuit of the present invention.

FIG. 8 is a diagram illustrating the principle of a switch circuit according to the present invention.

[Explanation of symbols]

1 ₁ , 1 ₂ , ... 1 _m Transducer element 3 ₁ , 3 ₂ , 3 _n Transmitted pulse generator 4 ₁ , 4 ₂ , 4 _m Analog switch 5 ₁ , 5 ₂ , 5 _n receiver 7a, 7b field effect transistor 8 emitting diodes 9 photovoltaic element 10 optically coupled device 14 ₁ to 14 _m switching element for controlling a current of the analog switch drive circuit 15, 16 light emitting diodes

Claims (2)

[Claims] 1. A switch circuit for operating an analog switch by applying a gate voltage of a field effect transistor by an optical coupling element composed of a light emitting diode and a photovoltaic element, for turning on the field effect transistor. A switching element that keeps the current of the light emitting diode in a constant state for a certain initial period, and a switching element that flows in a current of a magnitude necessary to give a gate voltage that keeps the field effect transistor in an ON state after the certain period. And a functional element that imparts the above-mentioned operation sequence, a switch circuit. 2. An ultrasonic diagnostic apparatus, which uses the switch circuit according to claim 1 to connect and switch a transducer element to a transmission pulse generator or a receiver.