JP3263126B2 - Ultrasound diagnostic equipment - Google Patents

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 switching a receiving circuit constant using a varicap diode.

[0002]

2. Description of the Related Art Here, a variable filter will be described as an example of a receiving circuit composed of varicap diodes.

Generally, in an ultrasonic diagnostic apparatus, a received signal is processed in a wide band for a B-mode image in order to improve resolution and sensitivity, and a signal in a narrow band (near a center frequency) is processed in a Doppler mode. Mode ultrasound images have been obtained. Such frequency band control is performed by a variable filter, and the variable filter is generally configured using a varicap diode.

FIG. 8 is a circuit diagram showing an LPF (low-pass filter) having two RC stages. When a varicap diode is used as a capacitor C in FIG. Then, 10 by varying the reverse voltage V _R
As shown in (1), the capacitance of the capacitor C is changed, thereby obtaining a desired filter band. The resistance R _B in Fig. 2 are those placed in order to prevent interference between the filter each other and the value of the normal number of [KΩ] to tens [KΩ].

[0005]

However, in such a conventional ultrasonic diagnostic apparatus, when the mode is switched for each ultrasonic rate signal which is a reference signal for determining the reception time and period of the echo signal, the rate signal is not changed. Each time, the setting of the varicap in the receiving circuit must be changed. Since a long transient response time determined by the resistance R _B of the varicap capacitance C and the control voltage line when changing the setting,
When the number of rates is large, the setting cannot be performed satisfactorily, and there is a disadvantage that the mode cannot be switched for each rate.

For example, R _B = 10 [KΩ], C = 500
When [pF / piece] is set, the varicap setting is changed, that is,
Since the time used for the transient response of the varicap is proportional to the time constant determined by R and C, the set time reaches about 100 μsec in the configurations of FIGS.

The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide an ultrasonic diagnostic apparatus capable of shortening the setting time of a varicap.

[0008]

In order to achieve the above object, the present invention provides an ultrasonic wave having a function of switching a receiving circuit constant which is constituted by using a varicap diode whose capacity can be adjusted by a reverse bias voltage from a control circuit. In the diagnostic apparatus, the control circuit includes a first voltage generation source that generates a predetermined voltage for setting the capacitance of the varicap diode to a predetermined value, and a second voltage generation source that generates a voltage higher than the predetermined voltage. When the capacitance is changed, the output terminal is switched in the order of the second voltage generation source and the first voltage generation source to apply a reverse bias voltage.

[0009]

With the above arrangement, the bias voltage applied to each varicap diode at the time of switching the receiving circuit constant such as the cutoff frequency of the variable filter becomes the maximum allowable value, and thereafter, is switched to the normal voltage. Therefore, the reverse voltage transient response reaches the predetermined value in a short time, and as a result, the time for changing the setting can be shortened.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a varicap diode used in the ultrasonic diagnostic apparatus according to the present embodiment and a control circuit thereof.

As shown in the figure, a plurality of varicap diodes (two in the figure) C _V1 and C _V2 are connected to a control circuit 2 so that their capacitances are controlled.

[0012] The control circuit 2,-option and a permissible maximum value V _max of the varicap diodes C _V1, C _V2 voltage V _C and the varicap diodes for determining the capacitance of C _V1, reverse voltage applied to the C _V2 The power supply unit 1 includes a power supply unit 1 for switching and outputting the output, and a parallel circuit of a diode D (D1, D2) and a resistor R (R1, R2).

The operation at the time of mode switching in such a configuration will be described with reference to a time chart shown in FIG. As shown in the figure, the mode switching is performed within the time when the rate signal S1 rises. Therefore, conventionally, as shown in the voltage V _R characteristics S3 in the figure, are applied when the rate signal S1 rises to voltage V _C to the varicap diodes C _V1, C _V2. At this time, since each of the varicap diodes C _V1 and C _V2 has a reverse voltage transient response characteristic, the desired capacitance is not instantaneously obtained but reaches the predetermined capacitance after time t _{2 as} shown by the curve S5. Therefore, the setting change cannot be completed while the rate signal S1 is rising.

[0014] Therefore, the output of the power supply unit 1 and the reverse voltage allowable maximum value V _max side in FIG. 1 at the time when the rate signal S1 rises in this embodiment, switching the voltage V _c side after a while (Fig. 2 S2). Thus, the reverse voltage transient response as shown by the curve S4, since reaches a predetermined value at time t _1, is the capacity of each varicap diodes C _V1, V _V2 can be short time Tokoro set further to.

Next, the reason for using the diodes D1 and D2 shown in FIG. 1 will be described.

The time constant τ of the varicap transient response is the capacitance C
And the resistance R _{B of the} bias line (R1, R2 in FIG. 1)
Is proportional to That is, the following equation (1) is obtained.

[0017] tau = R _B C where the capacitance C has a as in FIG. 3 as a function of reverse bias voltage V _R. That is, as shown in FIG. 3, when the voltage V _R is large, the time constant τ is small, and when V _R is small, τ is large. Therefore, when switching the V _R from the "large (e.g. 10V)" to "small (e.g. 2V)" requires a considerable time until V _R reaches V _C so gradually τ increases.

[0018] Then, it is conceivable to reduce the resistance R _B in order to reduce this tau, it can not be reduced R _B to prevent interference between the filters.
Therefore, the provided buffer 11 of low output impedance, as shown in FIG. 4, equivalently can lower R _B.
However, this method has a disadvantage that the number of buffers is required by the number of varicaps and the circuit scale is increased.

[0019] Therefore, to insert a diode D as shown in FIG. 5 in one direction only purpose of lowering the R _B equivalently. In this case the orientation of the diode D is to act on the fall of the V _B. This is because, at the rise, τ gradually decreases with time, so that the transition time can be relatively short, but at the fall, τ increases.

By using this diode D, V _C can be temporarily increased to V _max .

[0021] Thus, in this embodiment, it is possible to perform mode switching in a short set time by one end V _max control voltage V _R to the mode switching.

[0022] In the present embodiment has the switching function is provided on the reverse bias line, which may be added a function of setting temporarily V _max reverse voltage driver as shown in FIG. 6, for example. Alternatively, as shown in FIG. 7, a method of switching with a low ON-resistance analog SW may be used.

The present invention can also be applied to setting a delay time of a variable delay line constituted by a coil and a varicap diode. As shown in FIG. 11, the variable delay line has a delay amount τ =
√ (LC) is obtained, and the delay amount can be continuously varied by using a varicap diode as a capacitor. These delay times are also switched periodically for each rate, and the delay amount can be set in a short time by the circuit configuration shown in FIG. 1 as in the case of the variable filter described above.

[0024]

In the present invention, as described in the foregoing, the output of the maximum allowed V _max of the reverse voltage (second voltage source) provided in the power supply unit, at the time of mode switching from application of one V _max It is returned to the desired set voltage V _C. Therefore, it is possible to reduce the time for switching the reception circuit constant, and thereby obtain the effect of shortening the control time of the reception circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a time chart showing signals of the present embodiment and a conventional example.

FIG. 3 is a characteristic diagram showing a relationship between a voltage V _R and a time constant τ.

FIG. 4 is a circuit diagram when a buffer is used to reduce a time constant τ.

FIG. 5 is a circuit diagram when a diode is used to reduce the time constant τ.

FIG. 6 is a diagram showing a unit for switching an output voltage of a power supply unit.

FIG. 7 is a diagram showing another example of the means for switching the output voltage of the power supply unit.

FIG. 8 is a configuration diagram showing a conventional example.

FIG. 9 is a configuration diagram showing a conventional example.

FIG. 10 is a characteristic diagram showing a relationship between a reverse voltage V _R and a capacitance C.

FIG. 11 is a circuit diagram for obtaining a delay amount τ = √ (LC).

[Explanation of symbols]

_Reference Signs _List 1 power supply unit 2 control circuit C _V1 , C _V2 varicap diode 11 buffer

Claims (1)

(57) [Claims] 1. An ultrasonic diagnostic apparatus having a receiving circuit constant switching function configured by using a varicap diode whose capacity can be adjusted by a reverse bias voltage from a control circuit, wherein the control circuit has a capacitance of the varicap diode. Has a first voltage generation source for generating a predetermined voltage for setting the predetermined voltage to a predetermined value, and a second voltage generation source for generating a voltage higher than the predetermined voltage. An ultrasonic diagnostic apparatus characterized in that an output terminal is switched in the order of a voltage generation source and a first voltage generation source to apply a reverse bias voltage.