JP2008000506A - Ultrasonic diagnostic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ultrasonic diagnostic equipment protecting a receiving circuit from transmission signals without enlarging the scale of the circuit. <P>SOLUTION: A capacitor C1 is connected serially between a connecting point of a transmission circuit 3 and a preamplifier 11 of the receiving circuit 4, while a diode D1, a diode D2 and a resistor R1 are connected in parallel. The voltage of the transmission signal is applied to the both ends of the capacitor C1 so that complementary diodes D1 and D2 are not necessarily to have high voltage resistance. After passing the capacitor C1, the transmission signal is clamped by the complementary diodes D1 and D2 to protect the preamplifier 11 of the receiving circuit 4. Alternatively, the resistor R1 connected to a bias power supply Vref is provided to secure high input impedance of the preamplifier 11, to sufficiently reduce the capacity and size of the capacitor C1 and miniaturize the circuit scale. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus. Specifically, the present invention relates to a transmission / reception separation circuit that separates a transmission signal and a reception signal in an ultrasonic diagnostic apparatus and a preamplifier that amplifies the reception signal.

  In general, an ultrasonic diagnostic apparatus includes an ultrasonic probe, a transmission circuit, a reception circuit, and a transmission / reception separation circuit. The ultrasonic probe has a plurality of vibration elements. The transmission circuit has a plurality of transmitters corresponding to the respective vibration elements. Each transmitter has a transmission amplifier that amplifies the transmission signal. The receiving circuit has a plurality of receivers corresponding to each ultrasonic transducer. Each receiver has a preamplifier for amplifying the received signal. A signal line from the vibration element is connected to the preamplifier. A transmission / reception separation circuit is provided at a connection point between the transmission circuit and the reception circuit.

At the time of transmission, a high-voltage transmission signal (for example, 100 Vpp, 5 MHz) flows from the transmission circuit through the signal line to the ultrasonic probe. At the time of reception, a minute reception signal (for example, 1 Vpp or less) flows from the ultrasonic probe through the signal line to the reception circuit.
Since the transmission signal and the reception signal share one signal line, a high-voltage transmission signal flows into the reception circuit. Therefore, it is necessary to protect the preamplifier of the receiving circuit from the transmission signal.

  Therefore, an ultrasonic diagnostic apparatus has been proposed in which a protection circuit including a diode bridge and a switch is provided in the transmission / reception separation circuit to protect the preamplifier of the reception circuit from a transmission signal (see, for example, [Patent Document 1]).

JP 2005-318966 A

However, a protection circuit including a diode bridge has a problem that a high voltage diode is required to protect against a transmission signal. Furthermore, there is a problem that noise occurs because the operating resistance of the diode exists in the reception signal path.
In addition, a protection circuit including a switch has a problem that a switching signal for switching between a transmission mode and a reception mode is required. At the time of reception, the protection circuit operates as a grounded base amplifier, and the input impedance is reduced. Therefore, there is a problem that a large-capacitance capacitor is required to increase the time constant in order to pass the received signal sufficiently. During transmission, a high voltage is applied to the switch and the output terminal. Therefore, there is a problem that a high breakdown voltage element is necessary.

  The present invention has been made in view of the above problems, and an object thereof is to provide an ultrasonic diagnostic apparatus that protects a reception circuit from a transmission signal without increasing the circuit scale.

  In order to achieve the above-described object, the present invention provides an ultrasonic probe including an ultrasonic transducer that transmits and receives ultrasonic waves in a subject, a transmission unit that supplies a transmission signal to the ultrasonic transducer, A reception unit having a preamplifier for amplifying a reception signal from the ultrasonic transducer, an image processing unit for forming an ultrasonic image based on the reception signal output from the reception unit, and an image display for displaying the ultrasonic image An ultrasonic diagnostic apparatus comprising: a capacitor connected in series between a connection point of the transmitting unit and the receiving unit and an input of the preamplifier; and an input resistance circuit of the preamplifier viewed from the capacitor And a clamp circuit provided between the capacitor and the input of the preamplifier.

At the time of ultrasonic transmission, the transmission signal that has flowed into the capacitor is coupled by the capacitor to block the DC component, clamped by the clamp circuit, limited to a predetermined voltage range, and output to the preamplifier.
When receiving ultrasonic waves, the received signal passes through a high-pass filter composed of a capacitor and a resistor, and is input to a preamplifier and amplified.

The clamp circuit includes two diodes. One diode is connected in the forward direction between the input of the preamplifier and the first power supply, and the other diode is connected in the reverse direction between the input of the preamplifier and the ground or the second power supply (reference power supply).
The transmission signal is a signal having a large amplitude and is clamped because it is equal to or higher than the forward operation voltage Vf (0.6 V to 0.8 V) of the diode. Since the received signal is a signal having a small amplitude and does not exceed the forward operating voltage Vf of the diode, it is not clamped.

  Thus, since the voltage of the transmission signal is applied across the capacitor, the diode of the clamp circuit does not need to have a high breakdown voltage. Further, since the transmission signal is clamped by the clamp circuit after passing through the capacitor, the preamplifier is protected.

Regarding the clamp circuit, two diodes may be connected in antiparallel between the preamplifier input and the ground or the second power supply (reference power supply).
As a result, the reception signal having the amplitude at the center of the ground or the center of the second power supply can be input to the preamplifier.

The input resistance circuit includes a resistor provided between the input of the preamplifier and the bias power source.
As a result, the high input impedance characteristic of the preamplifier can be ensured, and the circuit scale can be reduced by sufficiently reducing the capacitance and size of the capacitor.

For the input resistance circuit, a switching element may be provided. When a switching element is provided, it is desirable to turn on the switching element when transmitting ultrasonic waves and to turn off the switching element when receiving ultrasonic waves.
Thus, even when it is difficult to on-chip a resistor having a large resistance value, it is possible to reduce the size such as an IC by using a switching element such as a field effect transistor instead of the resistor.

Further, it is desirable that the capacity of the capacitor be smaller than the equivalent capacity of the ultrasonic transducer.
Thereby, the load of the transmission amplifier of the transmission circuit can be suppressed.
The resistance value of the input resistance circuit is preferably a resistance value in which the cutoff frequency determined by the capacitance of the capacitor and the resistance value of the input resistance circuit is smaller than the frequency of the transmission signal.
Thereby, the loss and noise of a received signal can be suppressed.

  According to the present invention, it is possible to provide an ultrasonic diagnostic apparatus that protects a reception circuit from a transmission signal without increasing the circuit scale.

  Hereinafter, preferred embodiments of an ultrasonic diagnostic apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, the same reference numerals are given to components having substantially the same functional configuration, and redundant description is omitted.

(1. First embodiment)
First, the ultrasonic diagnostic apparatus 1 according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

(1-1. Configuration of the ultrasonic diagnostic apparatus 1)
FIG. 1 is a configuration diagram of the ultrasonic diagnostic apparatus 1.
The ultrasonic diagnostic apparatus 1 includes an ultrasonic probe 2, a transmission circuit 3, a reception circuit 4, a transmission / reception separation circuit 5, a control unit 6, an image processing unit 7, and an image display unit 8.

  The ultrasonic probe 2 has a plurality of ultrasonic transducers 9. The transmission circuit 3 has a plurality of transmitters corresponding to the ultrasonic transducers 9. Each transmitter has a transmission amplifier that amplifies the transmission signal. The receiving circuit 4 has a plurality of receivers corresponding to the ultrasonic transducers 9. Each receiver has a preamplifier for amplifying the received signal. A transmission / reception separation circuit 5 is provided at a connection point between the transmission circuit 3 and the reception circuit 4. The control unit 6 is a device that sends control signals to the transmission circuit 3 and the reception circuit 4.

  The ultrasonic diagnostic apparatus 1 sends a transmission signal from the transmission circuit 3 to the ultrasonic probe 2 via the transmission / reception separation circuit 5 and irradiates the ultrasonic signal from the ultrasonic probe 2 into the subject. The ultrasonic diagnostic apparatus 1 receives an ultrasonic signal reflected in the subject by the ultrasonic probe 2, sends the ultrasonic signal to the receiving circuit 4 through the transmission / reception separating circuit 5, and amplifies it by the preamplifier of the receiving circuit 4. The ultrasonic diagnostic apparatus 1 performs image processing on the ultrasonic signal by the image processing unit 7 and displays an image by the image display unit 8.

(1-2. Configuration of Transmission / Reception Separation Protection Circuit 10)
FIG. 2 is a configuration diagram of the transmission / reception separation protection circuit 10.
The transmission / reception separation protection circuit 10 is provided at a connection point between the transmission circuit 3 and the reception circuit 4. The transmission / reception separation protection circuit 10 includes a capacitor C1, a diode D1, a diode D2, a resistor R1, and the like. The transmission / reception separation protection circuit 10 has the function of the transmission / reception separation circuit 5 of FIG.
A capacitor C1 is connected in series between a connection point of the transmission circuit 3 and the preamplifier 11 of the reception circuit 4, and a diode D1, a diode D2, and a resistor R1 are connected in parallel.
The anode of the diode D1 and the cathode of the diode D2 are connected to the capacitor C1, the resistor R1, and the preamplifier 11. The cathode of the diode D1 is connected to the power supply Vdd. The anode of the diode D2 is grounded. The resistor R1 is connected to the bias power supply Vref.
The preamplifier 11 is a low noise amplifier (LNA) with an FET (Field Effect Transistor) input.

(1-3. Operation of transmission / reception separation protection circuit 10)
(1-3-1. Operation during ultrasonic transmission)
The transmission circuit 3 sends a transmission signal to the ultrasonic probe 2. The transmission amplifier of the transmission circuit 3 outputs a high-voltage transmission signal (for example, 100 Vpp, 2 to 10 MHz). The transmission signal flows into the capacitor C1. The transmission signal that has flowed into the capacitor C1 is coupled by the capacitor C1 to cut off the DC component, clamped by the diode D1 and the diode D2, becomes a predetermined voltage, and is output to the preamplifier 11.

The voltage of the transmission signal is applied to the capacitor C1 and output to the diode D1 and the diode D2. When the amplitude of the output voltage from the capacitor C1 is positive and is larger than a predetermined voltage (for example, 0.6V to 0.7V) compared to the power supply Vdd, the diode D1 operates, and the output voltage to the preamplifier 11 is It is clamped by [voltage value of power supply Vdd] + [predetermined voltage (for example, about +0.6 V)]. When the amplitude of the output voltage from the capacitor C1 is negative and is smaller than a predetermined voltage (for example, −0.6 V to −0.7 V), the diode D2 operates, and the output voltage to the preamplifier 11 is [predetermined voltage ( For example, about −0.6V)].
For example, when the voltage value of the power supply Vdd is 5V, the voltage when the transmission signal is input to the preamplifier 11 is limited to about −0.6V to + 5.6V. Therefore, the FET of the subsequent preamplifier 11 is not damaged.

  The current flowing through the diode D1 and the diode D2 is determined by the impedance of the capacitor C1. Further, since the capacitor C1 also serves as a load of the transmission amplifier of the transmission circuit 3, it is desirable that the capacitance is sufficiently smaller than the capacitance of the ultrasonic probe 2. On the other hand, it is desirable that the capacitor C1 has a large capacity in order to pass the received signal to a low frequency without attenuation. Therefore, it is desirable that the capacitance of the capacitor C1 be about several pF to several tens pF.

(1-3-2. Operation when receiving ultrasonic waves)
The received signal from the ultrasound probe 2 is very small. Therefore, the received signal is not clamped by the diode D1 and the diode D2. The received signal passes through a high-pass filter composed of a capacitor C1 and a resistor R1, and is input to the preamplifier 11 of the receiving circuit 4. The received signal is amplified by the preamplifier 11 and processed by the reception processing unit 12.

Regarding the noise of the received signal, the thermal noise due to the resistor R1 can be suppressed by making the resistor R1 sufficiently larger than the resistance of the signal source (the output impedance of the ultrasonic probe 2). Further, the capacitance of the capacitor C1 can be reduced by sufficiently increasing the resistance R1.
For example, when the capacitance of the capacitor C1 is 10 pF and the resistance value of the resistor R1 is 100 kΩ, the time constant τ is 1 μsec. The cut-off frequency (cutoff frequency) fc of the high-pass filter constituted by the capacitor C1 and the resistor R1 is fc = 1 / (2π · C1 · R1) ≈160 kHz. Since the frequencies of the transmission signal and the reception signal in the ultrasonic diagnostic apparatus are 2 to 10 MHz, the cutoff frequency is suitably about 100 kHz to 1 MHz. Therefore, when the capacitance of the capacitor C1 is 10 pF, it is desirable that the resistance value of the resistor R1 be 100 kΩ or more.

(1-4. Effect)
As described above, in the first embodiment, the capacitor is provided in series between the connection point of the transmission circuit and the preamplifier of the reception circuit, and the resistor connected to the complementary diode and the bias power supply is provided in parallel. Since the voltage of the transmission signal is applied across the capacitor, the complementary diode need not have a high breakdown voltage. Further, since the transmission signal is clamped by the complementary diode after passing through the capacitor, the preamplifier of the reception circuit is protected.

In addition, by providing a resistor connected to the bias power source, the high input impedance of the preamplifier can be ensured, the capacity and size of the capacitor can be sufficiently reduced, and the circuit scale can be reduced.
Furthermore, since the capacity of the capacitor can be made sufficiently smaller than the capacity of the ultrasonic probe, the load on the transmission amplifier of the transmission circuit does not increase.

(2. Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG.

(2-1. Configuration of Transmission / Reception Separation Protection Circuit 10a)
FIG. 3 is a configuration diagram of the transmission / reception separation protection circuit 10a.
The transmission / reception separation protection circuit 10a of the second embodiment uses a diode D3 and a diode D4 in place of the diode D1 and the diode D2 of the transmission / reception separation protection circuit 10 of the first embodiment.

The cathode of the diode D3 and the anode of the diode D4 are connected to the capacitor C1, the resistor R1, and the preamplifier 11. The anode of the diode D3 and the cathode of the diode D4 are grounded.
The preamplifier 11 of the first embodiment is an amplifier that operates over an input voltage range centered on a predetermined voltage value. The preamplifier 11a according to the second embodiment is an amplifier that operates in an input voltage range centered on the ground.

(2-2. Operation of transmission / reception separation protection circuit 10a)
The voltage of the transmission signal is applied to the capacitor C1 and output to the diode D1 and the diode D2. When the amplitude of the output voltage from the capacitor C1 is positive, the diode D4 operates and the output voltage to the preamplifier 11 is clamped at a predetermined positive voltage. When the amplitude of the output voltage from the capacitor C1 is negative, the diode D3 operates and the output voltage to the preamplifier 11 is clamped with a predetermined negative voltage. Therefore, the FET of the subsequent preamplifier 11 is not damaged.

(2-3. Effect)
As described above, also in the second embodiment, the same effect as in the first embodiment can be obtained. In addition, a reception signal having a ground-centered amplitude can be input to the preamplifier.

(3. Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG.

(3-1. Configuration of Transmission / Reception Separation Protection Circuit 10b)
FIG. 4 is a configuration diagram of the transmission / reception separation protection circuit 10b.
The transmission / reception separation protection circuit 10b according to the third embodiment uses a field effect transistor (FET) Q1 instead of the resistor R1 of the transmission / reception separation protection circuit 10 according to the first embodiment. . The controller 13 is a device that controls on / off of the field effect transistor Q1.

(3-2. Operation of transmission / reception separation protection circuit 10a)
At the time of transmission, the control unit 13 turns on the field effect transistor Q1, and the output voltage to the preamplifier 11 is clamped by the diode D1 and the diode D2. At the time of reception, the control unit 13 turns off the field effect transistor Q1, and the voltage of the bias power supply Vref is held at the input terminal of the preamplifier 11, and at the same time, the high input impedance of the preamplifier 11 is ensured.

(3-3. Effect)
As described above, the same effects as those of the first embodiment can be obtained in the third embodiment.
Even when it is difficult to on-chip a resistor having a large resistance value, an IC such as the transmission / reception separation protection circuit 10b can be realized by using an FET instead of the resistor.

(4. IC)
In recent years, when the number of channels is large as in a two-dimensional ultrasonic probe, it is difficult to provide a transmission / reception separation protection circuit and a reception circuit for each channel from the viewpoint of circuit scale and the number of cables. It is desirable that the cable length between the preamplifier and the ultrasonic transducer is also short. Therefore, it is desirable that at least a part of the transmission / reception separation protection circuit and the reception circuit is integrated into an IC and mounted on the ultrasonic probe portion. The transmission / reception separation protection circuit according to the first to third embodiments is composed of a complementary diode that does not require a high breakdown voltage and a small-capacitance capacitor, and is therefore suitable for IC implementation.

FIG. 5 is a diagram showing the inter-wiring capacitance.
In the case of an IC, it is desirable to provide an interwiring capacitance C2 between the wiring 14 and the wiring 15 on the circuit board 16. A small high voltage chip capacitor may be provided outside the IC.

(5. Other)
The preferred embodiments of the ultrasonic diagnostic apparatus according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

Configuration diagram of the ultrasonic diagnostic apparatus 1 Configuration diagram of transmission / reception separation protection circuit 10 Configuration diagram of transmission / reception separation protection circuit 10a Configuration diagram of transmission / reception separation protection circuit 10b Diagram showing capacitance between wires

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ......... Ultrasonic diagnostic apparatus 2 ......... Ultrasonic probe 3 ......... Transmission circuit 4 ......... Reception circuit 5 ......... Transmission / reception separation circuit 6, 13 ......... Control part 7 ......... Image processing Section 8... Image display section 9... Ultrasonic vibrator 10, 10 a, 10 b... Transmission / reception separation protection circuit 11... Preamplifier 12. ... Circuit boards C1, C2 ......... Capacitors (capacitance elements)
R1 ..... resistor (resistance element)
D1, D2, D3, D4 ......... Diode Q1 ......... Transistor Vdd, Vref ......... Power supply

Claims (6)

An ultrasonic probe including an ultrasonic transducer that transmits and receives ultrasonic waves in a subject, a transmission unit that supplies a transmission signal to the ultrasonic transducer, and a preamplifier that amplifies a reception signal from the ultrasonic transducer An ultrasonic diagnostic apparatus comprising: a receiving unit having: an image processing unit that forms an ultrasonic image based on a reception signal output from the receiving unit; and an image display unit that displays the ultrasonic image. ,
A capacitor connected in series between a connection point of the transmitter and the receiver and an input of the preamplifier;
An input resistance circuit of the preamplifier viewed from the capacitor;
A clamp circuit provided between the capacitor and the input of the preamplifier;
An ultrasonic diagnostic apparatus comprising:   The clamp circuit includes two diodes, one diode is connected in the forward direction between the input of the preamplifier and the first power supply, and the other diode is connected between the input of the preamplifier and the ground or the second power supply. The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic diagnostic apparatus is connected in a reverse direction.   The ultrasonic diagnostic apparatus according to claim 1, wherein the clamp circuit includes two diodes, and the two diodes are connected in antiparallel between a preamplifier input and a ground or a second power supply.   The ultrasonic diagnostic apparatus according to claim 1, wherein the input resistance circuit includes a resistor provided between an input of the preamplifier and a bias power source.   The input resistance circuit includes a switching element provided between the input of the preamplifier and a bias power source, and turns on the switching element when transmitting the ultrasonic wave and turns off the switching element when receiving the ultrasonic wave. The ultrasonic diagnostic apparatus according to any one of claims 1 to 3, characterized in that:   The capacitance of the capacitor is small compared to the equivalent capacitance of the ultrasonic transducer, and the resistance value of the input resistance circuit has a cutoff frequency determined by the capacitance of the capacitor and the resistance value of the input resistance circuit. The ultrasonic diagnostic apparatus according to any one of claims 1 to 5, wherein the resistance value is smaller than a frequency of the transmission signal.

Images