JPH03123880A - Signal generation circuit for ultrasonic diagnostic - Google Patents

Abstract

PURPOSE:To obtain a sweep waveform with stable frequency by applying a PLL control on an oscillation frequency of voltage control oscillator(VCO) using a reference signal at the ON time of a phase locked loop(PLL) and controlling an output voltage of voltage waveform generator. CONSTITUTION:At the ON state of a switch 6, the PLL is formed and an output of the VCO 1 is phase-locked to a frequency of the reference signal from a crystal oscillator 4, thereby the oscillation frequency coincides with the frequency of reference signal. Since the PLL is open and the phase lock is released when the switch 6 is in the OFF state, the sweep waveform, the frequency of which is varied in accordance with the output voltage of voltage waveform generator 2, is obtained by the VCO 1 from the frequency of reference signal. Thus, the PLL control is applied on the oscillation frequency of VCO 1 by using the reference signal at the ON time of switch 6 to control the output voltage of generator 2, and when the switch 6 is in the OFF time, the oscillation frequency of VCO 1 is controlled by the output voltage of generator 2 which is controlled by the operation of PLL.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used in an ultrasonic diagnostic device that transmits ultrasonic waves into a living body and receives the echoes to obtain a tomographic image of the living body. Related to signal generation circuits.

[Conventional technology]

BACKGROUND ART In an ultrasonic diagnostic apparatus that obtains tomographic images of a living body, there is a phenomenon in which a high-frequency component of an echo signal from a long distance decreases due to attenuation of ultrasonic waves, and its center frequency shifts to a lower frequency side.

Conventional ultrasonic diagnostic equipment takes this phenomenon into consideration, and by continuously changing the characteristics of a bandpass filter (BI'F) that passes echo signals converted into electrical signals during reception, For echo signals, images are formed using high frequency components to achieve high resolution.
For echo signals from a long distance, a method has been proposed in which dynamic filtering is performed by forming an image with low frequency components and increasing the diagnostic distance.

However, in the case of using a BPF with variable characteristics as described above, there is a problem that adjustment and maintenance thereof are difficult.

To solve this problem, for example, as disclosed in Japanese Patent Laid-Open No. 61-253047, a voltage controlled oscillator (VCO) is used to generate a local signal whose frequency sweeps during the reception period. As a result, an ultrasound diagnostic device has been proposed in which the echo signal is frequency-converted so that its center frequency is constant, and then filtered by a BPF with a fixed passband to obtain an effect similar to dynamic filtering. There is.

[Problem to be solved by the invention]

However, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-253047, when simply using a vCO to generate a local signal whose frequency sweeps, the circuit changes due to changes in the characteristics of the VCO over time. Since the performance is not constant, there is a problem that a sweep waveform with a stable frequency cannot be obtained, and there is also a problem that the circuit configuration for generating the sweep waveform in synchronization with the ultrasound transmission timing becomes complicated.

The present invention has been made in view of these conventional problems, and provides a signal generation circuit for an ultrasonic diagnostic device that is appropriately configured to obtain a frequency-stable sweep waveform with a simple circuit configuration. The purpose is to

[Means and operations for solving the problem] In order to achieve the above object, the present invention uses a voltage controlled oscillator (VCO).
, a voltage waveform generating means for generating a voltage waveform for controlling the oscillation frequency of this VCO, a reference signal generating means for generating a reference signal, and an output of this reference signal generating means and a voltage waveform for controlling the oscillation frequency of the VCO.
A phase comparator that compares the phases of the outputs of the VCO, and a low-pass filter that extracts low frequency components from the output of the phase comparator, so that the oscillation frequency of the VCO corresponds to the reference signal generated from the reference signal generating means. a phase-locked circuit that controls the output voltage waveform of the voltage waveform generating means based on the output of the low-pass filter so that the frequency
A loop (PLL) is configured, and control means for opening and closing the PLL is provided, thereby stabilizing a sweep waveform that changes within a predetermined range from a frequency corresponding to a reference signal generated by the reference signal generation means from the VCO. so that it occurs.

〔Example〕

FIG. 1 shows a first embodiment of the invention. VC
O1 controls its oscillation frequency by the output voltage of voltage waveform generator 2, and supplies the output of this VCO1 to one input terminal of phase comparator 3. The output (reference signal) of the crystal oscillator 4 is supplied to the other input terminal of the phase comparator 3, the phase difference with the output of the VCO 1 is detected, and the low frequency component of the output is extracted by the LPF 5. The output of this LPF 5 is supplied to the voltage waveform generator 2 via the switch 6, thereby controlling its output voltage so that the oscillation frequency of the VCO 1 matches the frequency of the reference signal from the crystal oscillator 4. Configure PLL.

Further, the switch 6 is set to 0 by a control signal from the control circuit 7.
N10FF is controlled to open and close the PLL, and in synchronization with this, a trigger pulse is supplied from the control circuit 7 to the voltage waveform generator 2, and its output voltage waveform is repeatedly supplied to the VCO 1.

FIG. 2 shows an example of a specific circuit configuration of the voltage waveform generator 2 shown in FIG. 1. In FIG. This voltage waveform generator 2 is
A bootstrap circuit 12 having an OP amplifier 11 for generating a ramp waveform, and a reference voltage -Vl and the output of the LPF 5 (DC bias voltage -V
d), and a switch 16 for controlling the repetition of the ramp waveform by a trigger pulse from the control circuit 7.

In this embodiment, a trigger pulse as shown in FIG. 3A is supplied to the switch 16 to cause the bootstrap circuit 12 to generate a ramp wave as shown in FIG. 3B. By adding the DC bias voltage -Vd from the LPF 5 in the adding circuit 15, a voltage waveform as shown in FIG. 3C is obtained. In addition,
In FIG. 3A, a period a is a period in which the switch 16 is ON, and in FIG. 1, the switch 6 is ON, that is, P
The period corresponds to the period in which LL is closed, and the period is the period in which the switch 16 is OFF, and in FIG. 1, the switch 6 is OFF.
F, that is, corresponds to the period during which the PLL is open.

With this configuration, the switch 6 is set to O in FIG.
In the N state, the PLL is configured and the output of vcot is phase-locked to the frequency of the reference signal from the crystal oscillator 4, so that its oscillation frequency matches the frequency of the reference signal, and when the switch 6 is OFF, the PLL is configured. Since the VCO 1 is opened and the phase lock is released, a sweep waveform whose frequency changes according to the output voltage of the voltage waveform generator 2 is obtained from the frequency of the reference signal from the VCO 1.

That is, when the crystal oscillator 4 generates a reference signal with a frequency f1 as shown in FIG. TeLPF
5 and switch 6, the output voltage of the voltage waveform generator 2 is controlled to vlo as shown in FIG.
PLL to match the frequency f1 of the reference signal of the crystal oscillator 4! 1141. After that, when the switch 6 is turned OFF, the PLL does not operate during that period, so the oscillation frequency of vCol changes from fl as the output voltage of the voltage waveform generator 2 changes from vl'' to V2°. Changes to f2.After that, switch 6 is set to 0N.
By repeating 10FF, a sweep waveform as shown in the fourth diagram in which the frequency always changes from fl to f2 is obtained from the VCO1.

As described above, according to this embodiment, when the switch 6 is ON, the oscillation frequency of the VCO 1 is controlled by the PLL using the reference signal.
The output voltage of the voltage waveform generator 2 is controlled by controlling the output voltage of the voltage waveform generator 2, and the oscillation frequency of the VCO 1 is controlled by the output voltage of the voltage waveform generator 2 controlled by the PLL operation when the switch 6 is OFF. With a circuit configuration, VCO
Even if the performance of the circuit is not constant due to changes in characteristics over time, etc., a sweep waveform with a stable frequency can be obtained.

FIG. 5 shows the configuration of an example of an ultrasonic diagnostic apparatus using the signal generating circuit according to the present invention, in which the present invention is applied to a local signal generating circuit that converts the frequency of an echo signal. The ultrasound transducer 21 is excited by a transmission pulse generated from the transmission circuit 23 in synchronization with a transmission timing pulse from the control circuit 22, thereby emitting ultrasound pulses into the living body. Echoes of the ultrasound emitted into the living body tissue are received by the ultrasound transducer 21 and converted into electrical echo signals, which are then sent to the preamplifier 2.
4 and then supplied to mixer 25.

The mixer 25 is supplied with a local signal whose frequency sweeps during the reception period from a local signal generation circuit 26 according to the present invention configured similarly to the signal generation circuit shown in FIG. In response to the shift of the center frequency of the echo signal to a lower frequency range, the echo signal is frequency-converted so that its center frequency remains constant. The output of this mixer 25 is a BPF with a fixed pass band.
27 to remove unnecessary components, the signal processing circuit 2
8, where necessary signal processing such as logarithmic compression is performed, and the ultrasonic image is displayed on the display device 29.

In this ultrasonic diagnostic apparatus, the operation of the control circuit 7 shown in FIG. 1 that constitutes the local signal generation circuit 26 is as follows.
The transmission timing pulse is transmitted by the control circuit 22 and supplied from the control circuit 22 to the transmission circuit 23 at the end of the PLL operation in the local signal generation circuit 26, that is, at the end of period a in FIGS. 3 and 4. Make it happen from time to time.

According to this ultrasonic diagnostic apparatus, the local signal generation circuit 2
Since it is possible to obtain a local signal with a sweep waveform with a stable frequency from 6, it is possible to accurately convert the frequency of the echo signal so that its center frequency remains constant. This effect can be stably obtained.

FIG. 6 shows a second embodiment of the invention. In this embodiment, in the ultrasonic diagnostic apparatus shown in FIG. 5, the output of vco i in the local signal generation circuit 26 and the transmission timing pulse sent out from the control circuit 22 are synchronized.

Therefore, in this embodiment, in the control circuit 22, the seventh
A burst pulse shown in FIG. 7B synchronized with the transmission timing pulse shown in FIG.

In this way, it is possible to obtain a local signal synchronized with the transmission pulse, so that flickering of the ultrasound image displayed on the display device 29 can be effectively suppressed. Also,
Since the burst pulse generated based on the transmission rate pulse is used as the reference signal, the crystal oscillator 4 shown in FIG. 1 is not required, and the cost can be reduced.

Note that this invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, in the above-described embodiment, a local signal is generated for converting the frequency of the echo signal so that its center frequency is constant. This invention can also be effectively applied.

〔Effect of the invention〕

As described above, according to the present invention, when the PLL is ON, the oscillation frequency of the VCO is controlled by the PLL using the reference signal to control the output voltage of the voltage waveform generator, and the PLL is turned ON.
Since the oscillation frequency of the VCO is controlled by the output voltage of the voltage waveform generator controlled by PLL operation during FF, the circuit configuration is simple, and the performance of the circuit is not constant due to changes in the characteristics of the VCO over time. Even in cases where the frequency is stable, it is possible to obtain a sweep waveform with a stable frequency.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing a first embodiment of the present invention.
Figures 3A to 3C are signal waveform diagrams for explaining its operation; Figures 4A to D are the embodiments shown in Figure 1; FIG. 5 is a diagram showing the configuration of an example of an ultrasonic diagnostic apparatus using the signal generation circuit according to the present invention, and FIG.
Figures 7A and 7B showing the embodiment are signal waveform diagrams for explaining the operation thereof. 1-・-VCO2-・Voltage waveform generation circuit 3-・Phase comparator 4-Crystal oscillator 5-・LPF
6- Switch 7-・Control circuit Tri-cut Hals Figure 2 1■ Figure 4 Figure 3 Figure 5

Claims (1)

[Claims] 1. A signal generation circuit for use in an ultrasound diagnostic device that transmits ultrasound waves into a living body and receives the echoes to obtain a tomographic image of the living body, the signal generation circuit comprising: a voltage controlled oscillator; , a voltage waveform generating means for generating a voltage waveform for controlling the oscillation frequency of the voltage controlled oscillator, a reference signal generating means for generating a reference signal, and a phase of the output of the reference signal generating means and the output of the voltage controlled oscillator. and a low-pass filter that extracts low frequency components from the output of the phase comparator, and the oscillation frequency of the voltage-controlled oscillator is determined from the reference signal generating means based on the output of the low-pass filter. A phase-locked circuit configured to control the output voltage waveform of the voltage waveform generating means so that the frequency corresponds to the generated reference signal.
1. A signal generation circuit for an ultrasonic diagnostic apparatus, comprising: a loop; and control means for opening and closing the phase-locked loop.