JPS6137837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal generator, for example, a video signal generator used to synchronize the output frequency of a video tape recorder (VTR) and the reception frequency of a television receiver (TV). The present invention relates to a signal generator suitable for an audio signal generation circuit.

The RF modulator of a VTR converts the signal received by the VTR or the signal played back from the recording tape into the form of television radio waves and sends it to the TV.The output frequency is fixed at a certain frequency or set to the frequency of several channels. There is. Therefore, in order to connect a TV to a VTR and project the received signal or playback signal onto the TV's cathode ray tube as an accurate image and obtain audio,
It is necessary that the output frequency of the VTR and the tuner frequency of the TV match. For this reason, VTR
The video signal system circuit is equipped with a video signal generator that generates a test video signal used only for video adjustment, and a signal generator that generates a test audio signal to tune the audio frequency. Ru. Due to its nature, the test signal generated by this signal generator requires highly accurate frequency and level settings.

FIG. 1 shows a conventional VTR audio signal system circuit to which a signal generator for test audio signals is added. Audio signal S given from magnetic tape, etc.
is applied to the signal switching circuit 4 after being subjected to signal processing such as amplification in the audio signal processing circuit 2 . This signal switching circuit 4 selectively switches the audio signal from the audio signal processing circuit 2 and the test audio signal generated by the signal generating circuit 6 based on a control signal given from the outside, and supplies it to the pre-emphasis amplifier 8. do. The audio signal corrected in the high frequency range by the pre-emphasis amplifier 8 is applied to the FM modulation circuit 12 together with the carrier wave of the audio carrier wave generation circuit 10, where it is converted into television radio waves by FM modulation, and then output to the output terminal. It is taken out from 14.

In this way, the signal generation circuit 6 in the conventional audio signal system circuit is installed independent of and in addition to the audio signal system, and moreover, the signal generation circuit 6 is installed in the audio signal system in addition to the audio signal system.
consists of a mechanical changeover switch operated from the outside. In addition, when adding the signal generation circuit 6 independently from the main circuit of the audio signal system,
It is necessary to insert a buffer circuit in the output section in order to harmonize with the pre-emphasis amplifier 8, and when the test audio signal is formed using a logic circuit in particular, the addition of such a buffer circuit will increase the number of circuit elements. As the number of circuits increases, the circuit configuration becomes complicated.

An object of the present invention is to provide a signal generating device that can form a signal using an input buffer circuit of an amplifier, and can simplify the circuit configuration by omitting a signal switching circuit, an independent buffer stage, etc. be.

The present invention provides an amplifier having a buffer circuit added to a signal input section, a constant current circuit that causes a drive current to flow through the buffer circuit of this amplifier, and a drive current that is added to the constant current circuit and supplies the drive current to the buffer circuit. The present invention is characterized by comprising a current variable circuit that causes the buffer circuit to generate a signal whose amplitude changes based on a switching signal applied from the outside and whose amplitude changes in response to the current change.

Embodiments of the present invention will be described in detail below with reference to the drawings.

Figure 2 shows the signal generator of this invention implemented.
This shows the audio signal system circuit of a VTR. In this audio signal system circuit, the same parts as in FIG. 1 are given the same reference numerals. The signal generator 16 forms an audio signal by sharing a buffer circuit installed at the signal input section of the pre-emphasis amplifier 8.
Therefore, the conventional signal switching circuit 4 is not required at all, and the reproduction signal input to the audio signal system is simply stopped, and in this state, the signal generation circuit 6 receives the control signal Sc, which is the basis of the audio signal frequency, such as a video signal. A prescribed audio signal can be generated by applying a switching signal obtained by dividing the frequency of the pulse generated for formation.

FIG. 3 shows an embodiment of the signal generating device 16. The pre-emphasis amplifier 8 is provided with an amplifier 20 for high frequency correction of the signal frequency and a buffer circuit 22. A pre-emphasis circuit 24 is added to the amplifier 20 for high frequency correction of the signal. That is, the output terminal 2 of the amplifier 20
A resistor 30 is connected between the feedback terminal 28 and the feedback terminal 28, and a resistor 32 and a capacitor 3 are connected in series between the feedback terminal 28 and the reference potential point (GND).
4 has been inserted.

The buffer circuit 22 installed at the input section of the amplifier 20 is configured as a current buffer with a transistor 36. The collector of the transistor 36 is applied with voltage Vcc from the drive power supply, and the base is connected to the input of an external signal. An input terminal 38 is formed. A reproduced audio signal is applied to this input terminal 38 by a signal source 42 via a resistor 40, and an output terminal 46 of a voltage source 44 formed of an integrated circuit together with a transistor 36 is applied to the resistor 48.
A voltage Va is applied through. Here, the signal source 42 refers to a signal supply source that supplies an audio signal, such as the audio signal processing circuit 2 in FIG. 2. Further, a filter capacitor 49 is connected between the output terminal 46 and the reference potential point (GND).

Signal generator 16 that generates a test audio signal
is configured to include the buffer circuit 22 as a part thereof. That is, the input terminal (+) of the amplifier 20 is connected to the emitter of the transistor 36, and a constant current circuit 50 for passing a constant current through the emitter is connected. and a resistor 56. A voltage source 54 sets a constant voltage Vb at the base of the transistor 52, and a resistor 56 connected to the emitter sets the emitter current of the transistor 52 to a constant value. This constant current circuit 50 includes a current variable circuit 5 that varies the emitter current based on a control signal Sc given from the outside.
8 is added. The variable current circuit 58 is composed of a transistor 60, resistors 62, 64, and a resistor 6.
2 and the transistor 60 are connected to the resistor 5.
6, and the base of the transistor 60 receives a control signal consisting of a switching signal from the outside.
It is designed so that Sc is given.

In this way, the signal generating device 16 is configured to include the buffer circuit 22 of the pre-emphasis amplifier 8, and the base potential of the transistor 60 is set to a potential at which the transistor 60 becomes conductive or a potential at which the transistor 60 becomes non-conductive. If set to any potential, the buffer circuit 22 is connected to the signal source 4.
It functions as a normal buffer circuit that guides the input signal given from 2 to the amplifier 20.

Further, when the signal generator 16 is operated to generate a test audio signal, the signal input from the signal source 42 is stopped, and at the same time, the control signal Sc is applied to the base of the transistor 60. This control signal Sc
is composed of a signal, such as a switching pulse having the frequency of the test audio signal, which turns the transistor 60 on and off at a constant frequency. In this way, by inputting the control signal Sc, the transistor 6
0 is in a non-conducting state, only the resistor 56 is connected to the emitter of the transistor 52, and when the transistor 60 is in a conducting state, both the resistor 56 and the resistor 62 are connected to the emitter of the transistor 52.
and transistor 60 are connected, and a change occurs in the current flowing through transistor 52. Here, if the resistance values of the resistors 56 and 62 are Rea and Reb, and the currents generated when the transistor 60 is turned on and off are Ion and Ioff, the current ratio (Ion:Ioff) is
Rea: Rea・Reb/(Rea+Reb). on the other hand,
The emitter potential of the transistor 36 has a value lower than the base bias voltage Va by the base-emitter voltage Vbe generated by the emitter current of the transistor 36. Generally, the value of this base-emitter voltage Vbe is correlated with the current flowing through the transistor 36 when its operation is in the linear operating range.For example, if the emitter current is doubled, the voltage will drop by about 18 mV. arise. Therefore, if the emitter current ratio of the transistor 36 is accurately set by the relative ratio of the resistance values Rea and Reb of the resistors 56 and 62, the difference voltage value of the base-emitter voltage Vbe, that is, the absolute value of the signal amplitude can be set arbitrarily. Can be set to . As a result, a test audio signal with a constant output level is formed by changing the voltage between the base and emitter of the transistor 36 in accordance with the frequency of the control signal Sc, and this audio signal is subjected to high frequency correction through the amplifier 20. After that, FM from output terminal 26
The signal is applied to the modulation circuit 12.

In this manner, the signal generator 16 forms an audio signal by sharing the buffer circuit 22 of the pre-emphasis amplifier 8, and does not affect the reproduction audio signal processing of the normal audio signal system. Furthermore, as is clear from the examples, there is no signal switching circuit such as a mechanical switch that requires external operation, and the circuit configuration is extremely simplified.
It is configured as a signal generating means with an absolute level suitable for IC implementation with high resistance ratio accuracy.

FIG. 4 shows a specific embodiment of the signal generator of the present invention. The same parts as in the circuit of the previous embodiment are given the same reference numerals. That is, the amplifier 20 includes transistors 70, 72, 74, 76, 78, 8
0, 82, 84, 86, 88, 90, diode 92, 94, resistor 96, 98, 100, 102,
104, 106 and a capacitor 108, transistors 86, 88, 90 and a resistor 10
2, 104, and 106 constitute a constant current circuit. With this configuration, an audio signal having a constant voltage amplitude set internally can be generated, and this signal can be directly input and extracted.

Although the embodiment has been described as an audio signal system circuit for a VTR, any signal system may be used as long as it is configured as a signal generator using the buffer circuit in an amplifier having a buffer circuit at the front stage of this invention. However, it is not limited to this type of signal processing system. Also, the amplifier only needs to have a buffer circuit.
Any circuit configuration may be used.

As described above, according to the present invention, it is possible to form a signal using an input buffer circuit of an amplifier, and to simplify the circuit configuration by omitting a signal switching circuit, an independent buffer stage, etc.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the audio signal system circuit of a conventional VTR, Fig. 2 is a block diagram showing the audio signal system circuit of a VTR using the signal generator of the present invention, and Fig. 3 is a block diagram showing the audio signal system circuit of a VTR using the signal generator of the present invention. FIG. 4 is a circuit diagram showing a specific embodiment of the signal generating device of the present invention. 8... Pre-emphasis amplifier, 16... Signal generator, 20... Amplifier, 22... Buffer circuit, 24... Pre-emphasis circuit, 50... Constant current circuit, 58... Current variable circuit.

Claims (1)

[Claims] 1. An amplifier to which a buffer circuit is added to the signal input section, a constant current circuit that causes a drive current to flow through the buffer circuit of this amplifier, and a drive current that is added to the constant current circuit and is applied to the buffer circuit from the outside. and a current variable circuit that causes the buffer circuit to generate a signal whose amplitude changes based on a switching signal generated by the current, and whose amplitude changes in response to the current change.