JPH09192132A - Ultrasonic reception circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve distance resolution and to improve the resolution of a diagnostic image by writing digital data, with which the reflect signal of output of a delay line is minimized, in a correction circuit having a diode, for which a resistance component is linearly varied, connected to a terminal resistor. SOLUTION: A switching circuit 20 decides the delay amounts of delay lines on respective printed circuit boards 7a, 7b...7n by controlling the changeover of switches S., S,...Sn on the respective printed circuit boards 7a, 7b...7n according to the control signal of a control circuit 21 and further transmits an ultrasonic signal from a reception amplifier group 6 to a prescribed delay line. Then, arbitrary data for regulating the resistance component of the diode itself at the following correction circuit are written in a ROM 22 of the control circuit 21 in advance so as to minimize the reflection of the delay line. Between the respective output terminals of the ROM 22 and the delay lines on the respective printed circuit boards 7a-7n, correction circuits 23a, 23b...23n composed of capacitors C and diodes D, for which the resistance components are linearly varied, are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus for obtaining a tomographic image of a living body using ultrasonic waves, and particularly to a delay line so that a reflected wave of an ultrasonic wave reception signal output from the delay line is minimized. The present invention relates to an ultrasonic receiving circuit in which the characteristic impedance and the terminating resistance are matched.

[0002]

2. Description of the Related Art FIG. 3 shows a block diagram of a conventional ultrasonic diagnostic apparatus. The transmission circuit section includes a vibrator drive circuit 4 and a transmission delay circuit 5. The transmission delay circuit 5 generates a pulse provided with a predetermined delay time determined from the ultrasonic transmission focus point. This transmission delay pulse is
The oscillator drive circuit 4 allows the ultrasonic probe oscillator 1 ₁
It is converted into high voltage pulses sufficient to drive ~ 1 _n .

The high-voltage pulse thus delayed is separated from the reception signal by the transmission / reception separation circuit 3,
The ultrasonic wave is applied to the ultrasonic probe 1 via the high-voltage switch group 2, and the ultrasonic wave is radiated to the living body. High voltage switch group 2
For example, in order to perform electronic linear scanning, several ultrasonic transducers that actually transmit and receive ultrasonic waves are selected, and they are switched so that they are shifted one by one each time transmission and reception are repeated.

A received signal from each transducer of the ultrasonic probe 1 is amplified by a preamplifier group 6 and then input to a reception delay circuit 7. Here, a predetermined delay time determined by the reception focus point is given to the received signal, and the received signal is added to the received signals from other transducers to be phased.

The phasing output signal thus phasing-added is subjected to logarithmic compression by the logarithmic amplifier 8 and envelope detection by the detection circuit 9 to generate an analog video signal.

This video signal is input to a DSC (digital scan converter) unit 10 and an A / D converter 11
Is converted into a digital image signal and written in the memory 12. The digital image data on the memory 12 is
Each time the ultrasonic beam is electronically scanned, it is converted into an analog video signal by the D / A converter 15, and an ultrasonic tomographic image is displayed on the TV monitor 16.

Reference numeral 15 is a CPU which controls the switch 2, the transmission delay circuit 5, the memory 12 and the like by an instruction signal from the panel 14.

[0008]

In FIG. 1, the reception signal from each transducer amplified by the reception preamplifier group 6 is input to the tap switching circuit 20 of the delay lines D _{1 to} D _n . Here, the control circuit 21 controls to select an arbitrary tap of the delay line in order to give a predetermined delay time determined by the focus point to the received signal. The tap switching circuit 20 inputs the received signal from each transducer from an arbitrary tap, adds a predetermined delay time, and performs phasing addition. Further, the buffer amplifiers B _{1 to} B _n are inserted between the delay lines and have a function of suppressing the attenuation when the received signal passes through the delay lines. The terminating resistance R _t is a fixed resistor having a constant value equal to the characteristic impedance Z ₀ of the delay line. By terminating with the terminating resistor R _t , all the received signals input from each tap of the delay line are delayed and transmitted to the output end, and the signal (reflected signal) sent back to the input end disappears.

[0009] However, the characteristic of the characteristic impedance Z ₀ is a delay line mounted on a printed circuit board each of the delay line, since there is a variation of about ± 10%, terminating when terminated with resistors R _t of the resistance value of the fixed non It becomes perfect and reflection occurs due to mismatch (mismatch). That is, as shown in FIG. 2, the output (b) of the input (a) of the delay line becomes a reception signal delayed by the delay time Td, but after this reception signal, a reflection signal appears due to the above-mentioned mismatching, and the reception signal The tailing of the pulse becomes longer and the distance resolution of the pulse (resolution in the direction of the ultrasonic beam) is reduced. Therefore, there is a problem that the resolution of the diagnostic image deteriorates.

[0010]

In order to achieve the above object,
The present invention is characterized in that means for correcting matching with the characteristic impedance of the delay line is provided.

According to the means of the present invention, even if the characteristic impedance of the delay line mounted on each printed circuit board is varied, the resistance value of the terminating resistor is electronically changed to perform matching, and the delay line due to the mismatching is used. It works to suppress reflection. As a result, the tailing of the received signal pulse is eliminated, the distance resolution is improved, and the resolution of the diagnostic image is improved.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, reference numerals 7a, 7b ... 7n denote printed boards on which the tap switching and reception delay circuit 7 of FIG. 3 is mounted. Each printed circuit board has a buffer amplifier B ₁ ,
Delay lines D ₁ , D ₂ ... D _n connected in series via B ₂ ... B _n and the delay lines D ₁ , D ₂ ... D _n
Selection switch S for varying the delay amount of
₁ , S ₂ ... S _n are mounted. The output end θ ₁ of the delay lines D ₁ , D ₂ ... D _n of the printed circuit board 7a is connected to the input end I ₂ of the delay line of the next printed circuit board 7b, and the output end of the delay line of the printed circuit board 7b is further connected to the output end θ _1. It is connected to the input terminal of the next stage. That is, the input / output terminals of the delay lines of the printed circuit boards 7a, 7b ... 7n are connected in series, and the delayed signal appears at the output terminal θ _n of the delay line of the final printed circuit board 7n. The respective switches S ₁ , S ₂ ... S _n of the respective printed boards 7a, 7b ... 7n are switched by the delay line tap switching circuit 20. The switching circuit 20 controls the switching of the switches of each printed circuit board by the control signal of the control circuit 21, and determines the delay amount of the delay line of each printed circuit board. The sound wave signal is transmitted to a predetermined delay line. A ROM 22 is connected to the control circuit 21.

Arbitrary data for adjusting the resistance component of the diode itself of the following correction circuit is written in the ROM 22 in advance so as to minimize the reflection of the delay line. R
A correction circuit 2 including a D / A, a resistor R, a capacitor C for cutting a DC voltage, and a diode between each output terminal of the OM 22 and the delay line of each printed circuit board 7a to 7n.
3a, 23b ... 23n are provided. The diode D is, for example, a PIN diode well known as a high frequency variable element, and is capable of changing a high frequency series resistance in a wide range while maintaining linearity with respect to a signal by controlling a direct current flowing through a PIN junction. Is something that can be done.
Next, the means for impedance matching will be described.
After mounting the delay line etc. on the printed circuit board,
For example, the inspector, under the control of the control circuit 21, transmits the ultrasonic signal US via the reception preamplifier group 6 and the tap switching circuit 20 to the delay lines D ₁ , D _2, ... D _{n of the} printed circuit boards 7a, 7b, ... Send to. The tap switching circuit 20 switches the switches S ₁ , S ₂ ... S _n of the printed circuit boards 7 a, 7 b ... 7 _n according to the focus point of the ultrasonic wave reception signal, and sets the delay amount corresponding to the focus point. In this case, since the characteristic impedance Z ₀ of the delay line of each printed circuit board has a variation of ± 10%, impedance matching cannot be achieved only by the terminating resistor R _t .

In the embodiment of the present invention, the control circuit 2
Under the control of No. 1, the arbitrary data previously written in the ROM 22 is converted into a digital signal, which is sequentially read out to correct the correction circuit 23.
a, 23b ... 23n. This digital signal is D / A
Is converted into an analog signal and the resistance value of the diode fluctuates linearly. Since the resistance value of the diode of the correction circuit in each stage fluctuates linearly, the fluctuation value of this resistance is added to the termination resistance R _t . Inspector is ROM22
It is checked which digital value sequentially read from the one minimizes the reflected signal in FIG. 2, that is, matches the characteristic impedance Z ₀ of the delay line of each stage, and fixes the value in the ROM 22.

As described above, at the manufacturing stage of the ultrasonic diagnostic apparatus, the reflected signal is minimized in advance by matching the impedance of the characteristic impedance of the delay line with the impedance of the terminating resistor by linearly changing the resistance of the diode of the correction circuit. Therefore, when the ultrasonic diagnostic apparatus is used for diagnosis, fixed data that matches the characteristic impedance of the delay line of each stage is constantly read from the ROM 22 to the correction circuits 23a to 23n. The reflected signal due to the delay line of the transmitted ultrasonic wave reception signal is minimized.

[0016]

As described above, according to the present invention, the resistance value of the terminating resistor can be arbitrarily changed according to the variation in the characteristic impedance of the delay line, so that the optimum impedance matching can always be achieved and the delay Minimize line reflections. As a result, the tailing of the pulse waveform of the received signal is improved, so that the distance resolution is improved, and the resolution of the diagnostic image is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of an ultrasonic receiving circuit according to the present invention.

FIG. 2 is a waveform diagram of reflection of a received signal pulse.

FIG. 3 is a block diagram of a conventional ultrasonic diagnostic apparatus.

[Explanation of symbols]

1 Ultrasonic probe 1 ₁ to 1 _n Ultrasonic transducer 2 High voltage switch group 3 Transmission / reception separation circuit 4 Transducer drive circuit group 5 Transmission delay circuit 6 Reception preamplifier group 7 Reception delay circuit D _{1 to} D _n Delay line B _{1 to} B _n buffer amplifier S _{1 to} S _n tap selection changeover switch 20 delay line tap changeover circuit 21 control circuit 22 ROM 23a to 23n matching correction circuit

Claims (1)

[Claims] 1. A linear system comprising a delay line for delaying an ultrasonic wave reception signal from a probe according to a focus point and a terminating resistor for matching impedance with a characteristic impedance of the delay line. An ultrasonic receiving circuit characterized in that a correction circuit having a diode whose resistance is variable is connected to the terminating resistor, and digital data in which the reflected signal of the output of the delay line is minimized is written in the correction circuit.