JP3069720B2 - Infinite impedance reproduction detection CW Doppler receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an ultrasonic CW Doppler diagnostic apparatus which saves parts and power consumption.

[0002]

2. Description of the Related Art With respect to an ultrasonic CW Doppler diagnostic apparatus, particularly a fetal heart rate detector, a high-frequency amplifier is omitted in a receiving section in order to simplify a circuit in order to reduce the amount of components and power consumption and to reduce the size and weight. An example in which a circuit configuration of a direct detection type is employed and an infinite impedance detection circuit is employed as the detection circuit can be found in, for example, Japanese Patent Application Laid-Open No. 3-23850.

[0003]

In the above conventional method,
Even when a detection method other than infinite impedance detection is used, the noise figure is lower than that of a method equipped with a high-frequency amplifier having a positive power gain because the first stage of the receiver is lossy and does not have a positive power gain. There was a problem of inferiority.

[0004]

In the present invention, the above problem is not solved by adopting a direct detection type circuit configuration in which the high frequency amplifier is omitted in the receiving section and employing a detection circuit having a positive power gain. In particular, an infinite impedance detection circuit is arranged so as to perform reproduction detection while utilizing its features.

[0005]

FIG. 2 is a circuit diagram showing an example of a fetal heart rate detector including a first-stage direct detection circuit according to a preferred embodiment of the present invention. In FIG. It is an example of a first stage direct detection circuit which is an embodiment. Compared with the corresponding portions in FIGS. 1 and 2 in the above-mentioned Japanese Patent Application Laid-Open No. 3-23850, the circuit structure is completely the same, but important component constants are different, and therefore the operation mode is completely different.

FIGS. 1 and 2 in the above-mentioned Japanese Patent Application Laid-Open No. 3-23850 are presented as FIGS. 3 and 4, respectively. The portion surrounded by a dotted line in the figure is the relevant portion of interest here. Hereinafter, this is abbreviated as a conventional circuit.

That is, in the circuit of the present invention (FIG. 1), an infinite impedance detection circuit that operates like an oscillation is realized as follows. The circuit specifications in the preferred embodiment are as follows. Q2 2SK715V (Sharp cut-off JFET with standard value gm = 50mS) Cin About 10PF (Input capacity (Ciss) of Q2) R1 33Kohm R2 62Kohm C1 150PF C2 330PF T2 (L2) Core (also serves as bobbin), base, shield case Sumida 2166-278 type secondary winding L
2 has a self-inductance of about 250 μH, a QL (load Q) value of about 25 to 30, and an internal parallel stray capacitance (not shown) of about 10 PF. Ultrasonic frequency 3 adopted under operating conditions
Tune to MHz. + EBB 4.3 to 6.8 V Here, the value of the capacitor C1 between the source of Q2 and the ground of the circuit is 150 PF, much smaller than several thousand PF to several μF in the conventional circuit, and the input capacitance Cin of Q2 is (About 10 PF) at most about 15 times. That is, the voltage dividing ratio formed by C1 and Cin is not so small that the circuit oscillates, but not so large that the action of the positive feedback can be ignored as in the conventional circuit. For this reason, this circuit has a positive feedback at a high frequency based on the same operating principle as the Colpitts oscillation circuit when viewed from the tuning transformer T2. As a whole, the operation of the oscillation circuit is performed while the detection circuit operates, that is, the reproduction detection is performed. Operate the circuit.

[0010] A detection circuit operating in a mode of oscillation is called a reproduction detection circuit, and it is well known that there is an inherent gain depending on the degree of reproduction. In the case of FIG.
If is smaller than approximately 100 PF, a complete oscillation state occurs, and the detection operation is not performed. On the other hand, if it is more than 330 PF, the property of the regenerative detection almost disappears, and only simple infinite impedance detection is performed. Only when the value of C1 is within the above range as an example, stable reproduction detection is performed, and as an example, an additional gain of 6 to 9 dB is obtained. In that state, a good noise figure of about 2 dB or less is obtained. If the feedback is too strong, the noise figure will return even if it does not oscillate.

The transition point from the oscillating state to the occurrence of oscillation is another factor that determines the value of gm during the operation of Q2. The drain current during the operation determined by R2 and the pinch-off characteristic of Q2 is large. Have the right. As an example, when the pinch-off voltage of Q2 is about -0.5 V, the above-mentioned value of R2 (62 Kohm) is a preferable example. In this case, the DC value of the drain current is about 8 μA. Of course, specific circuit constants will depend on the design conditions of each circuit, and thus the values of the circuit constants themselves do not define the present invention. It is important that the infinite impedance detection circuit can stably perform reproduction detection by setting appropriate circuit constants in this way, taking into account the stray capacitance of the circuit.

The reproduction detection itself can use various other methods. For example, the input tuning transformer may be provided with a feedback winding or tap to perform necessary positive feedback, or may be viewed from the gate. Necessary positive feedback can also be performed using stray capacitance on the drain side instead of stray capacitance on the source side. In addition, as the active element to be used, any element including a bipolar transistor and the like in addition to the junction FET as in the example described here can be used. However, it is most advantageous to perform the regeneration detection by modifying the infinite impedance detection circuit using the junction FET described above in terms of the number of parts and the simplicity of the circuit.

FIG. 2 shows the whole analog circuit section of an example of the fetal heartbeat detector including the infinite impedance reproduction detection CW Doppler receiving circuit of the present invention. In this, Q1
And its surroundings are a carrier transmitting circuit, and the area around Q2 is an infinite impedance reproduction detecting circuit, between which a pair of transducers (T) (R) forming a known CW Doppler probe is inserted. ing. U1 is an audio amplifier that also serves as a Doppler filter (low-cut filter), and drives an earphone via a low-frequency transformer T3.
Here, a large-amplitude carrier appearing at the collector of Q1 is rectified by D1 to increase the voltage of the boosted power source +
An EBB is obtained and used as a drain power supply for Q2 to improve the dynamic range defined by its DC operating point. In Q2, the detection output is further amplified and extracted from the drain side. The additional circuit on the source side (a series circuit of 0.1 μF and 6.2 KΩ) is provided for providing a gain in a low frequency region, so that Colpitts-type reproduction detection operation is not disturbed.

FIG. 5 is a digital circuit cooperating with the circuit of FIG. 2, in which the ultra-low power CPU (U11) is permanently connected to the battery and is always powered on;
The input of the power-on command push button switch S11 is continuously monitored by the operation of the resident running program, and when it is pressed, the semiconductor switch S1 is turned on to turn on the power of the analog portion without delay. On the other hand, at the same time, the CPU starts a software or hardware timed timer, and continues to monitor the audio output at the output terminal of U1 (FIG. 2) at its A / D conversion input port, if it is above a certain level. In this case, the timer is kept reset, and if no signal continues for about 1 to 2 minutes, the power is forcibly turned off to prevent useless consumption of the battery.

Instead of counting the timed timer by detecting such a no-signal state, the object can be achieved by simply forcibly turning off the power for a predetermined time after the power is turned on. However, in order to perform continuous monitoring for a long time, it is inconvenient to forcibly turn off the signal during signal sampling, so that a function of counting a timed timer by detecting such a no-signal state is required.

An absolute time generating circuit (ABS.TIMER) integrated with the CPU is used as a time standard for the operation of the timed timer. This absolute time generation circuit is also permanently connected to the battery, and always prepares information on years, months, days, hours, and minutes from the point of manufacture, or on calendar dates.

The absolute time information provided by the absolute time generation circuit is combined with device code information unique to each device, such as the serial number of the device, which is imprinted on the CPU, and is used for D / A conversion of the CPU. At the output port, the code signal is periodically converted to an intermittent audio frequency domain code signal, generated, and applied to the input of U1 (FIG. 2) at an appropriate level. As an example, a time of 250 ms per minute is spent for this. During that time, the CPU does not monitor the audio output level to check whether there is no signal.

The periodic generation of such device code and time code in an unchangeable form after production and addition to the audio output is accomplished by recording the audio signal, that is, the fetal Doppler signal, and reproducing it later to reproduce the fetal signal. This is useful for preventing confusion when performing analysis or the like.

FIG. 6 is a diagram showing an example of a state where the present apparatus is housed in a housing. In this case, the electronic circuit, the battery, the transmitting / receiving vibrators, and the like are all integrated and housed in the substantially cylindrical housing, and only the push button switch for the power-on command allows the operation unit to be seen outside. . At the end of assembling, the entire structure, including the earphone cord drawer, the push button switch operating part, and the sound opening, is implemented to achieve a water-tight structure. Potting with resin. As a result, the mounted batteries cannot be replaced after assembly.

That is, when the battery is used until the end of its life, the entire device is discarded. According to such a disposable design and structure, the battery is a primary battery, and there is no need to open and close the casing for replacement. Therefore, the entire structure, manufacturing procedure,
In addition, drastic simplification of safety design becomes possible, which greatly contributes to cost reduction of the apparatus.

【The invention's effect】

As has been made clear in the above description, according to the present invention, a fetal heart rate detector having good sensitivity, small size, light weight, and long battery life is suitable for personal use by pregnant women. This is useful because it can be put to practical use. Further, the apparatus of the present invention can be used not only for auscultating a fetal Doppler signal, but also for separately analyzing a collected fetal Doppler signal for use in a non-stress test or the like.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of an infinite impedance reproduction detection circuit according to the present invention.

FIG. 2 is a diagram illustrating an example of a fetal heartbeat detector using the infinite impedance reproduction detection circuit according to the present invention.

FIG. 3 is a diagram illustrating an example of an infinite impedance detection circuit that is not reproduction detection.

FIG. 4 is a diagram illustrating another example of an infinite impedance detection circuit that is not reproduction detection.

FIG. 5 is a diagram for explaining a digital circuit that operates in cooperation with the circuit of FIG. 2;

FIG. 6 is a diagram illustrating an example of a mechanical structure of a fetal heartbeat detector using the infinite impedance reproduction detection circuit according to the present invention. In this, (1) housing (2) acoustic opening (3) transmitting and receiving transducers (4) battery (5) electronic circuit (6) residual space (7) push button switch (8) earphone cord

Claims (3)

(57) [Claims] 1. A CW Doppler receiver configured to introduce a received signal obtained from a receiving oscillator into a detection circuit without amplifying the reception signal, wherein the detection circuit is an infinite impedance reproduction detection circuit. CW Doppler receiver. 2. A fetal heart rate detector comprising the CW Doppler receiver according to claim 1, wherein the power supply of the infinite impedance detection circuit is configured to be boosted and supplied from a battery power supply. , Fetal heart rate detector. 3. The fetal heartbeat detector according to claim 2, wherein the power supply supplied to the infinite impedance detection circuit and boosted from the battery power supply is obtained by rectifying the large amplitude carrier generated by the transmission circuit. A fetal heart rate detector characterized by having such a configuration.