JPS6315763Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a signal detection circuit device, and improves the coupling method between a local oscillation circuit and a resonant circuit in a signal detection circuit of a capacitive video disc playback device, for example. The present invention also relates to a signal detection circuit device that suppresses fluctuations in signal detection level due to component variations in a resonant circuit or a detection circuit.

[Technical background of the invention and its problems]

Generally, in a capacitive video disk playback device, a signal recorded on a disk is detected and played back as a change in capacitance using a signal playback stylus.

FIG. 1 is a circuit diagram of a signal detection circuit of a capacitance type video disk reproducing apparatus, and FIG. 2 is a characteristic diagram showing the relationship between frequency f and output voltage V _OE of the circuit shown in FIG. 1.

As shown in Figure 1, signal detection circuits can be roughly divided into
It can be classified into three circuits: 915MHz local oscillation circuit a, resonance circuit b, and detection circuit c. 915M
The Hz local oscillator circuit a consists of a 915MHz oscillator 1 and a coupling coil 2, and the resonant circuit b consists of a disk
A capacitance 3 between the stylus, a resonant capacitor 4,
The detection circuit c includes a resonant coil 5, a coupling coil 6, a detection diode 7, and a capacitor 8.
and a CR circuit with 9 resistors.
A detection voltage V _OE (V) is output to out.

The FM signal is recorded on the disk and appears as a capacitance of 3 between the stylus of the cartridge and the disk. This capacitor 3 constitutes a part of the resonant circuit b. On the other hand, regarding the output characteristics of the signal detection circuit, the horizontal axis represents the frequency (MHz), and the vertical axis represents the detection voltage V _OE
(V), it is as shown in FIG.
V _OE Max is the output voltage corresponding to resonance of the resonant circuit c. It is fixed so that the 915 MHz of the local oscillation circuit a falls on the slope part of the resonance characteristic of the resonance circuit c. In this way, when the capacitance 3 changes, the resonant frequency changes. Therefore, 915MHz
will be modulated by the capacitance 3. If this is detected by the detection circuit c, the FM signal of the disk can be detected.

Figure 3 is an actual circuit diagram of a conventional signal detection circuit.
FIG. 4 is a characteristic diagram showing the forward voltage V _F current I _F characteristics and reverse voltage V _R current I _R characteristics of the detection diode 24, and FIG. 5 is the emitter resistance 16 of the local oscillation circuit a.
FIG. 3 is a characteristic diagram showing the relationship between the resistance value R _E and the oscillation output P _O.

As shown in FIG. 3, the local oscillation circuit a has a bias resistor 11 connected between the base of the oscillation transistor 15 and the ground, the base is connected to the DC power supply +B via the bias resistor 10, and the collector is connected to the
It is connected to DC power supply +B via coils 13 and 14. Further, there is a ground capacitor 12 between the base and ground, and an emitter resistor 16 for bias control is connected between the emitter and ground. Resistor 16 is composed of a variable resistor. A circuit consisting of a pattern inductor 17 and a variable capacitor 18 is connected between the collector and ground. A pattern inductor 17 is then used to electrically couple the local oscillation circuit a and the resonant circuit b.
A coupling pattern inductor 19 is disposed between the pattern inductor 20 and the pattern inductor 20 . Both ends of the coupling pattern inductor 19 are grounded. Resonant circuit b is a resonant pattern/inductor 2
0, a capacitor 21 and a varactor diode 22 connected in series. Note that the cathode side of the varactor diode 22 is grounded. The detection circuit c includes a coupling pattern inductor 23 for electrically coupling to the resonance pattern inductor 20, a detection diode 24 connected in series with this, and a cathode of this diode 24.
It is composed of a capacitor 25 and a resistor 26 which are connected in parallel to each other between the ground, and the cathode side of the diode 24 is used as the output terminal OUT of the detection output. still,
Pattern inductors 17, 19, 20, and 23 are inductances using patterns on printed wiring boards.

In such a configuration, the oscillation output level of the local oscillation circuit a changes due to variations in circuit constants. As a result, the maximum value V _OE Max of the detected output voltage shown in FIG. 2 changes. When this value changes, the apparent operating point remains the same, but the maximum value
Since the relative value between V _OE Max and the operating point V _s changes, the actual operating point changes. If the actual operating point changes, the signal detection level and frequency characteristics will change and the performance of the signal detection circuit will deteriorate. As a countermeasure for this,
The local oscillation circuit a is adjusted to obtain the desired detection circuit characteristics.
It is controlled by varying the emitter resistance R _E. By the way, this detection circuit characteristic is based on resonance circuit b (inductor 20, capacitor 21,
It also changes depending on the characteristics of the varactor diode 22) and the V _F -I _F characteristics and V _R -I _R characteristics of the detection diode 24. For example, regarding the forward direction characteristics of the detection diode 24, as shown in FIG. If d, then even if the characteristics are as shown in Figure 4B, or if a defect in the reverse current I _R occurs as shown in Figure 4D, the emitter resistance value R of local oscillator circuit a _can be By controlling it, it is possible to obtain the detection circuit characteristics as shown in FIG. However, this is limited to the control range A of the output characteristics of the local oscillation circuit a as shown in FIG. If the desired detection circuit characteristics cannot be obtained by adjusting the resistance value _RE , the product will be determined to be defective at the adjustment stage of the manufacturing process.

For example, with respect to the forward characteristics of the detection diode 24 shown in FIG. 4, if the forward current I _F1 is required to obtain the desired detection circuit characteristics, both in case of a good product (A) and in case of a defective product (B). requires forward voltage V _F1 for good product A, and forward voltage V _F2 for defective product B. Voltage
V _F2 is approximately twice as high as voltage V _F1 , and therefore local oscillation circuit a needs to oscillate 6 (dB) higher. Therefore, even if the detection diode 24 is defective, the resistance value R _E shown in FIG.
If it is within the control range A based on the adjustment, the device will be shipped as a non-defective device. the result,
There was a problem in that defects occurred in the detection diode 24 after shipment. In addition, if the product is shipped in the above condition and placed on the market, if it is a defective product, the oscillation circuit a will oscillate 6 (dB) higher, which may cause interference to nearby electronic devices or lead to legal violations. There was a problem in that it generated unnecessary radiation that was subject to regulations.

[Purpose of invention]

In view of the above-mentioned points, an object of the present invention is to improve the method of electrically coupling between a local oscillation circuit and a resonant circuit in a signal detection circuit of a capacitive video disc playback device, for example. It is an object of the present invention to provide a signal detection circuit device made up of only truly good products by surely eliminating semi-defective devices caused by component variations in a detection circuit.

[Summary of the idea]

The signal detection circuit device of the present invention eliminates the conventional method of electrically coupling between the local oscillation circuit and the resonant circuit using mutual inductance, and instead couples the above circuits using a variable capacitor to connect the local oscillation circuit to the resonant circuit. By inserting a carrier wave into a resonant circuit and obtaining a detection signal in a detection circuit, the variable capacitor can be adjusted to obtain desired detection circuit characteristics.

[Example of idea]

Embodiments of the present invention will be described below based on the drawings.

FIG. 6 is a circuit diagram of the signal detection circuit device according to the present invention, and FIG. 7 is the variable capacitor 2 shown in FIG.
8 is a characteristic diagram showing the relationship between the oscillation output P _O and the capacitance value C of No. 8. FIG. In FIG. 6, parts having the same functions as those of the circuit shown in FIG. 3 are given the same reference numerals and will be explained.

In FIG. 6, a resistor 11 is connected between the base of the oscillation transistor 15 of the local oscillation circuit a and the ground, the base is connected to the DC power supply +B via the bias resistor 10, and the collector is connected to the chiyoke coil 1.
It is connected to DC power supply +B via terminals 3 and 14.
Further, there is a ground capacitor 12 between the base and the ground, a fixed resistor 27 is connected between the emitter and the ground, and a pattern inductor 17 and a variable capacitance element 18 are connected in series between the collector and the ground. One end of the variable capacitor 28 is connected to the connection point between the pattern inductor 17 and the variable capacitor 18, and the other end is connected to the connection point between the pattern inductor 20, capacitor 21, and varactor diode 22 of the resonant circuit b. Connected. The resonant circuit b is made up of a resonant pattern inductor 20, a capacitor 21, and a varactor diode 22 connected in series, and one end is grounded. Resonance pattern/
The inductor 20 is a coupling pattern of the detection circuit c.
It is arranged so as to be electrically coupled to the inductor 23. The detection circuit c includes a coupling pattern inductor 23 whose one end is grounded and a detection diode 24.
and connect a capacitor 2 between its cathode and ground.
5 and resistor 26 are connected in parallel, and the detection diode 2
The cathode of No. 4 is used as the output terminal out. Note that the pattern inductors 17, 20, and 23 are inductances using patterns on printed wiring boards.

In such a configuration, the oscillation output level of the local oscillation circuit a was conventionally adjusted using a variable resistor 16 as shown in FIG. Instead of electrically coupling between the local oscillation circuit a and the resonant circuit b, which was done using the conventional method, a variable capacitor 28 is used to connect the two circuits, and the capacitance value C is changed to create the desired detection circuit. It is adjusted to suit the characteristics. In this case, the relationship between the variable capacitance value C and the oscillation output P _O is as shown in Figure 7, so
Oscillation output can be controlled stably. That is, the variable capacitor 28 is a resonant circuit b.
Since it is connected in series with the capacitor 21 and the varactor diode 22, the variable capacitor 28
Even if the oscillation frequency is varied, it can be adjusted with almost no effect on the oscillation frequency. Therefore, if the variation in the signal detection level due to the capacitance value C is investigated in advance, it is possible to select a detection circuit with desired detection circuit characteristics. In this way, the variable capacitance value C can be set to identify and eliminate component variations that occur in the resonant circuit or the detection circuit, such as the cases of defective products as shown in Figure 4 B and D, thereby producing a highly reliable signal. A detection circuit can be realized.

[Effect of idea]

As described above, in the signal detection circuit of the capacitance type video disk reproducing device, by electrically connecting the oscillation circuit and the resonant circuit through a variable capacitance capacitor, the output of the oscillation circuit can be stably controlled, and the fluctuation of the signal detection level caused by the component variation of the resonant circuit and the detection circuit can be suppressed. Therefore, it has the advantage that a highly reliable signal detection circuit can be realized without defective components.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a signal detection circuit of a capacitive video disc playback device, Fig. 2 is a characteristic diagram showing the relationship between frequency and detection voltage of the circuit shown in Fig. 1;
Figure 3 is a specific circuit diagram of a conventional signal detection circuit.
Fig. 4 is a characteristic diagram showing the forward and reverse characteristics of the detection diode, Fig. 5 is a characteristic diagram showing the relationship between variable resistance value and oscillation output of the local oscillation circuit, and Fig. 6 is a signal detection circuit according to the present invention. The circuit diagram of the device, FIG. 7, is a characteristic diagram showing the relationship between the capacitance value of the variable capacitor and the oscillation output. a...Oscillation circuit (local oscillation circuit), b...Resonance circuit, c...Detection circuit, 10, 11...Bias resistance, 12...Grounding capacitance, 13, 14...Chiyoke coil, 15...Oscillation transistor, 17,
20, 23... pattern inductor, 18, 2
8...Variable capacitor, 21, 25...Capacitor, 22...Varactor diode, 24...
...detection diode, 26, 27...resistance.

Claims (1)

[Scope of utility model registration request] Capacitive video in which the oscillation frequency oscillated by the oscillation circuit is modulated via a resonant circuit whose resonant frequency changes according to the change in capacitance detected by the disk, and then the signal is detected by the detection circuit.・
In the signal detection circuit of a disc playback device, the oscillation circuit and the resonance circuit are connected through a variable capacitor, and the detection circuit characteristics are controlled by adjusting the variable capacitor. signal detection circuit device.