JPH05237098A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PURPOSE:To provide a transducing circuit of an ultrasonic diagnostic apparatus which stabilizes a DC bias of a are-amplifier of a receiving circuit immediately after the transmission to amplify a received signal normally immediately after the transmission from a specimen. CONSTITUTION:An receiving analog switch 4 is provided between a driver circuit 1 and a pre-amplifier 5 to cut the receiving analog switch 4 only for a specified time at the time of transmission and immediately after the transmission. The cutting of the receiving analog switch 4 reduces effect of the capacitance of a transmitted pulse. Thus, changes in DC bias of the pre-amplifier 5 becomes limited thereby enabling the receiving of a close range signal with the shortening of saturation time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission / reception circuit of an ultrasonic diagnostic apparatus, and more particularly to stabilizing DC bias of a preamplifier.

[0002]

2. Description of the Related Art A conventional ultrasonic diagnostic apparatus selects a group of elements forming a transmission / reception aperture from a plurality of transducers arranged in an array and mutually determines drive pulses to be applied to these elements. A beam focused at a predetermined position is formed by shifting the time, and the beam is scanned to form one screen by moving the aperture while sequentially shifting the element group. In the sector scanning, the aperture is not moved.
Such an electronic scanning device has a transmitting / receiving circuit of at least the number of apertures. Further, in the single plate vibrator, the transmission / reception circuit for one channel is used.

[0003]

The above-mentioned conventional technique does not consider the DC bias fluctuation immediately after the transmission, and has a problem that the DC bias of the preamplifier 5 changes. Since a general amplifier requires the bias of the first-stage transistor 51, AC coupling is performed by connecting the capacitor. Immediately after the transmission of a high voltage (about 100 V), diode clipping occurs due to ringing and the like, but the bias fluctuates.

FIG. 3 shows a time chart showing the operating state of the conventional transmission / reception circuit. Ringing occurs after generation of a rectangular pulse of 100 V, the input terminal A of the preamplifier 5 is pulled to the negative side as shown in the figure, and returns to the set value at the RC time constant. When the set DC bias of the preamplifier 5 is Vb and the maximum input voltage is ± Vinm, and the potential of the input terminal A of the preamplifier 5 exceeds ± Vinm, the preamplifier 5 operates in a saturated state during that time. Moreover, since the DC bias is changed even within ± Vinm, the original performance cannot be obtained, and there is a problem in processing a short-distance signal from the subject.

An object of the present invention is to shorten the time during which the preamplifier is in a saturated state and normally amplify the signal immediately after transmission.

[0006]

In order to achieve the above object, a receiving analog switch 4 is provided between a wave transmitting circuit for driving an ultrasonic transducer and a wave receiving circuit for amplifying a received signal. The wave receiving analog switch 4 is turned off during the wave transmission and for a predetermined time immediately after the wave transmission.

[0007]

The capacitance C is set by turning off the receiving analog switch 4 at the time of wave transmission and for a predetermined time immediately after the wave transmission.
The influence on the preamplifier 5 is reduced, the DC bias fluctuation of the preamplifier 5 is reduced, and the time during which the preamplifier 5 is in a saturated state is shortened. As a result, a signal from a shorter distance can be received.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention. Figure 1 (a)
The basic configuration of the transmission / reception circuit of the embodiment is shown in FIG. The high voltage (up to 300 V) output from the driver (wave transmission) circuit 1 is applied to the vibrator 3 through the transmission / reception separation circuit 2 and a sound wave is transmitted. The received signal is input from the transmission / reception separating circuit 2 to the preamplifier 5 of the receiving circuit through the receiving analog switch 4. FIG. 1B shows a time chart of the embodiment. The analog reception switch is turned off during transmission and for a predetermined time immediately after transmission.

As shown in FIG. 4, an ultrasonic transducer generally has an acoustic lens 6 for converging an ultrasonic beam on its front surface. Assuming that the thickness t of the acoustic lens 6 and the speed of sound in the acoustic lens 6 are v, the reflection signal on the lens surface is T = 2.
Observed after t / v hours. Therefore, the preamplifier 5 does not need to operate normally from the start of transmission to T.

Therefore, as shown in FIG. 5, when the receiving analog switch 4 is turned on, ± Vi during the process of recovering the potential by the DC potential of the input terminal A of the preamplifier 5 and the time constant of RC.
The off time is set so that the time until the preamplifier 5 becomes operable within the nm is within T. After that, by turning on the reception analog switch 4, the reception signal from the subject is input to the preamplifier 5. At this point, the operation of the preamplifier 5 has been restored.

In the case of the electronic scanning type device, the operation is the same except that a high breakdown voltage analog switch for selecting the vibrator 3 is interposed between the transmission / reception separating circuit 2 and the vibrator 3 shown in FIG. is there.

Another embodiment is shown in FIG. When the transmission trigger pulse is input to the DA terminal, the gate of N5 becomes low level, P1 and N1 are turned on by the capacitance CA, current is supplied to the vibrator 3, and the vibrator 3 becomes high voltage. After that, the gate of N5 becomes high level, conversely, N5 and N2 are turned on and the vibrator 3 becomes low level, and a high voltage pulse is substantially applied to the vibrator 3 to emit ultrasonic waves. At this time, the preamplifier 5 and the receiving analog switch 4 are protected by being clipped by the diode D1. At this time, when the receiving analog switch 4 is turned off, the potential change of the AC couple capacitor C becomes n
The change in the electric potential is small compared with the case where it is generated only through the drain-source off capacitance of No. 3 and is not turned off. Therefore, the input terminal A of the preamplifier 5 becomes more stable, and as shown in the time chart of FIG. 5, the time during which the preamplifier 5 is in the saturated state can be shortened.

When a large number of pulses are transmitted, the same effect can be obtained by turning off the receiving analog switch 4 within the round trip time from the transmission of the last pulse to the acoustic lens as described above. .. Further, in a probe having a distance to the subject such as a mechanical sector and a radial scan as shown in FIG. 6, the off time of the receiving switch 4 is set to the subject as in the acoustic lens described above. The same effect can be obtained by setting the distance within the round-trip time. In this case, ignoring the outer cover 9, the sound velocity v in the acoustic lens described above corresponds to the sound velocity of the acoustic couple liquid 8 and the thickness t corresponds to the distance 7 to the subject.

[0014]

According to the present invention, in the transmission / reception circuit of the ultrasonic diagnostic apparatus, the bias fluctuation of the preamplifier immediately after the transmission can be reduced, so that the reflection from the short distance by the subject immediately after the transmission can be reduced. The signal can be normally amplified.

[Brief description of drawings]

FIG. 1 is a transmission / reception circuit diagram showing an embodiment according to the present invention.

FIG. 2 is a wave transmission / reception circuit diagram showing another embodiment according to the present invention.

FIG. 3 is a timing chart of an operating state of a conventional transmission / reception circuit.

FIG. 4 is a cross-sectional view of the tip portion of the ultrasonic probe.

FIG. 5 is a timing chart of operating states of the wave transmission / reception circuit according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a distance to a subject of a mechanical scan.

[Explanation of symbols]

1 ... Driver circuit, 2 ... Transmission / reception separation circuit, 3 ... Oscillator, 4
… Receiving analog switch, 5… Preamplifier.

Claims (1)

[Claims] 1. An apparatus for driving an ultrasonic transducer in a device for driving an ultrasonic transducer to emit ultrasonic waves to a subject and receiving reflected waves from the subject to obtain a tomographic image of the subject. A switch is provided between the wave transmitting circuit for amplifying the received signal and the wave receiving circuit for amplifying the received signal, and the switch is turned off during the wave transmitting and for a predetermined time immediately after the wave transmitting. Sound wave diagnostic device.