JP2548157B2 - Gain control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is designed to switch an integrated circuit (IC) amplifier to either of two amplifiers and perform variable gain control of one of the amplifiers. The present invention relates to a gain control circuit that can be controlled by a potential applied from one terminal.

SUMMARY OF THE INVENTION The present invention is an integrated circuit having a variable gain amplifier whose gain is determined by the current value of a variable current source, in which first and second potentials are applied from one terminal and a current mirror circuit is used. By controlling the current of the variable current source and switching to the gain of either system as a two-system amplifier in which one system is capable of variable gain control, the switching of the gain of the two systems and the gain of one system This is a gain control circuit that enables adjustment from one terminal, reduces the number of terminals of the integrated circuit, reduces the cost of the integrated circuit, and improves the degree of freedom in designing the integrated circuit.

[Prior Art] For example, in a signal recording circuit for a metal tape (MP tape) and a vapor deposition tape (ME tape) used in an 8 mm VTR (video tape recorder), depending on the tape used, a signal level, especially a low frequency It is necessary to switch the signal level.

As this signal level switching circuit, conventionally, as shown in FIG. 8, for example, an amplifier 100 having a constant gain (amplification factor) K is used when a metal tape is used, and a gain different from the above K is given when a vapor deposition tape is used. A gain control circuit in which a voltage control type amplifier (VCA: voltage controlled amplifier) 101 is switched by a changeover switch 102 and used is used.

Here, the changeover switch 102 is controlled by a binary signal (+ 5V, 0V) given from the outside by the switch 103 or the like.
In addition, the VCA can be preset (factory set) by the semi-fixed volume control 104, which generally improves the degree of freedom in subsequent circuit design.

[Problems to be Solved by the Invention] Range of the conventional gain control circuit shown by the dotted line (FIG. 8)
When the IC is integrated into the IC, that IC has a terminal T ₁₀ for gain control of VCA.
And user control terminal for switching metal tape / deposited tape
It is necessary to provide two pins of T ₁₁ , which has a drawback of increasing the number of terminal pins of the IC. Increasing the number of IC terminal pins
This will increase the size of the IC, which will increase costs. Further, if the shape of the IC is to be kept as it is, it is necessary to reduce the number of other input / output pins, which is a problem that reduces the degree of freedom in IC design.

The present invention is to solve the above-mentioned drawbacks and problems, in an integrated circuit of an amplifier including a variable gain amplifier such as VCA, switching the system of the amplifier and controlling the gain of VCA with one terminal, It is an object to reduce the cost of an integrated circuit and improve the degree of freedom in designing the integrated circuit.

[Means for Solving the Problems] Means for achieving the above object in the present invention is an integrated circuit having a variable gain amplifier, the gain of which is determined according to the current value of a variable current source. A first transistor connected to one terminal of the integrated circuit and having a first potential and a second potential selectively applied to the one terminal from outside the integrated circuit to the control electrode; An input differential circuit comprising a second transistor having a differential pair with the first transistor and having a constant voltage source connected to the control electrode; and a controlled electrode of the first transistor of the input differential circuit connected to the first differential circuit. A current mirror circuit comprising a third transistor and a fourth transistor paired with the third transistor and controlling a variable current source of the variable gain amplifier. A switch circuit for selectively applying the fixed first electric potential and the adjustable second electric potential from a section, and when the second electric potential is applied to the one terminal, the switch circuit is provided. The gain control circuit is characterized in that the variable current source is controlled via the current mirror circuit by adjusting the potential of the variable gain amplifier to adjust the gain of the variable gain amplifier.

[Operation] The present invention selectively applies, from one terminal of an integrated circuit, a first potential and a second potential each of which takes a value in a different range, and according to the first potential and the second potential. The variable current source is controlled via the input differential circuit and the current mirror circuit, and the gains of different systems are switched first. At the same time as the switching, on the switching side by the second potential, the second potential is adjusted to adjust the current value of the variable current source and the gain of the variable gain amplifier can be adjusted.

As described above, the number of terminals is reduced by switching the amplifier system and adjusting the variable gain amplifier with one terminal.
Further, the gain control circuit can be commonly used even when the first potential and the second potential are applied, and a portion that does not operate due to a selection switch or the like is eliminated, which contributes to cost reduction of the integrated circuit.

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

FIG. 1 is a block diagram for explaining the principle of one embodiment of the present invention. The integrated circuit (hereinafter abbreviated as IC) 1 is
8mm VTR recording amplifier with input terminal V _IN and output terminal V
_{Has OUT} . This IC1 has the function of switching to different gains when the tape used is metal (MP) tape and vapor deposition (ME) tape, and at least one gain can be externally controlled (adjusted). Is configured. In order to perform the switching and the control (adjustment) of one of the switched gains, a control voltage (first potential,
One terminal T ₁ for inputting a second potential) is provided.

The IC1 of this embodiment has two different gains for one VCA3.
Give by. Therefore, the present embodiment has a simplified circuit configuration in which no changeover switch and a circuit portion which does not operate due to the changeover exist, and there is no waste. For this reason, the gain switching circuit 7 is provided, the input side is connected to the terminal T ₁ , and when the first potential V ₁ is detected, a control amount that provides a constant gain K to VCA 3 is transmitted, and the second When the potential V _{2 of} is detected, a control amount proportional to the value is sent out. In this way, the relationship between the control voltage input from the terminal T ₁ and the gain V _OUT / V _IN can be designed as shown in FIG. 2, for example.

The actual circuit of this embodiment is configured as shown in FIG. 3, for example. A well-known circuit disclosed in Japanese Patent Publication No. 48-20932 can be used as VCA3, and its current gain is I ₂ when the current of the current source 31 is I ₁ and the current flowing through the transistor Q ₅ is I _2.
/ I ₁ This I ₂ is configured to be controlled by the control voltage V ₁ or V ₂ by the gain switching circuit 7 described later.

Gain control circuit 7 includes a differential circuit 72 composed of a transistor Q _1, Q ₂ and a current source 71, a first current mirror circuit 73 consisting of a transistor Q _3, Q _4, transistors Q _5, Q
_{It is} composed of a second current mirror circuit 74 composed of ₆ or the like. The base of _one npn transistor Q ₁ of the differential circuit 72 is connected to the terminal T ₁ and receives the control voltage V ₁ or V ₂ . The base of the other npn transistor Q ₂ has a constant voltage source 7 of V ₁ value.
5 is connected, and the emitters of the transistors Q ₁ and Q ₂ are each connected to a current source 71 whose one end is connected to the ground via a resistor. The collector of the transistor Q ₂ is connected to the + B power source, and the collector of the transistor Q ₁ is connected to the npn transistor Q ₃ side of the first current mirror circuit 73. The other pnp transistor Q ₄ of the first current mirror circuit 73 is connected to one transistor Q ₅ of the second current mirror circuit 74, and the other transistor Q ₆ also serves as a part of the circuit of VCA 3. The current mirror circuit has a function of making the current flowing through one transistor equal to the current flowing through the other transistor.

The control voltage applied to terminal T ₁ is switch 6 and volume VR.
_One of the fixed terminals of the volume VR ₁ is connected to the + B power source via the resistor R ₁ and the other is connected to the ground via the resistor R _{2 although} it is composed of _{1 and the} like. The potential due to the resistance R ₂
If it is set to V ₁ , the second potential V ₂ given from the variable terminal of the volume VR ₁ has a relationship of V ₁ ≦ V ₂ .

In the above configuration, the terminal T ₁ has the first potential on the MP tape side.
When V ₁ is inputted, respectively to the transistors Q _1, Q ₂ is I ₃ /
A current of 2 flows, and when the second potential V ₂ on the ME tape side that is larger than V ₁ is input, the current flowing through the transistor Q ₁ increases, and the increased current increases the first current mirror circuit 73.
And flows as a current I ₂ of VCA3 via the second current mirror circuit 74. In this case, the increasing current value is I _{3 at the} maximum, so that it is possible to control up to a double gain. That is, the relationship between the control voltage and the gain is as shown in FIG.
The constant gain switched by V ₁ is K = I ₃ / 2I ₁ , and the control range of the gain switched by the second potential is I ₃ / 2I _{1 to} I ₃ / I ₁ .

In the above example, the MP tape side was set to a fixed gain, and the ME
Although the side has a variable gain, the ME tape side (voltage V ₂ ) is fixed by changing the potential of the constant voltage source, and the MP tape side (voltage
It is obvious that V ₁ ) can be made variable, and both can be made variable.

Furthermore, in the above embodiment, the gain control characteristic is set to the second control characteristic.
Although it is as shown in FIGS. 4 and 5, it may be as shown in, for example, FIG. 5, and in this case, there is an advantage that the gain control range by the second potential can be widened. The circuit for realizing the gain characteristic of FIG. 5 is the first current mirror circuit 73 of FIG.
It suffices to provide a current source 76, which is switched in parallel, as shown in FIG. This switching detects the control voltage applied to the terminal T ₁ with the level detector 77 and + B power source and current source.
This is done by turning on / off a switch 78 interposed between 76.

When the first potential V ₁ is applied to the above circuit from the terminal T ₁ ,
It is detected by the level detector 77 and the switch 78
Is turned on and the current I ₄ from the current source 76 is inserted into the input side of the second current mirror circuit 74, so that I ₂ = I
_3/2 + current I ₄ flows. Here, when the I ₄ = I _3/4, the gain when the first potential becomes _{I 2 / I 1 = (3/4} ) · (I 3 / I 1). In addition, the control voltage is a second potential higher than V ₁ by a predetermined potential.
When V ₂ is applied, it is detected by the level detector 77, the switch 78 is turned off, and the current inserted into the input of the second current mirror circuit 74 is only the current of the first current mirror circuit 73. It has the same structure as. That is, the gain at this time is controlled to (1/2) · I ₃ / I _{1 to} I ₃ / I ₁ .

In the following, an improved example for solving the problem of the circuit of the conventional example shown in FIG. 8 will be shown for reference in accordance with the gist of the present embodiment. FIG. 7 is a block diagram showing an improved example thereof. Integrated circuit (below
Reference numeral 1 is an 8 mm VTR memory amplifier, which has an input terminal V _IN and an output terminal V _OUT . This IC1 has a function of switching to different gains depending on whether the tape used is a metal (MP) tape or a vapor deposition (ME) tape, and at least one of the gains is controllable from the outside. In order to control the switching and gain,
One terminal T ₁ for inputting the control voltage is provided.

An amplifier 2 for giving a constant gain K to the IC1, a voltage control type amplifier (hereinafter abbreviated as VCA) 3 ', both amplifiers 2,
The switch 4 for switching the 3'output is integrated. The input side of each amplifier 2, 3'is connected to the input terminal V _IN , the output of the switch 4 is connected to the output terminal V _OUT , and VCA
The control input side of 3'is connected to terminal T ₁ .

The terminal T ₁ has a first electric potential V ₁ and a second electric potential V 2 applied thereto.
The potential V ₂ of the output is identified. For example, when V ₁ (V ₁ <V ₂ ) is input, the output is set to high level (“H”), and when V ₂ is input, the output is set to low level (“L”). ") Is connected to the comparator 5. The output of the comparator 5 is connected to the control input side of the switch 4, and if the output is "H", it is switched to the amplifier 2 side, and if the output is "L", it is switched to the VCA3 'side. As the switch 4, for example, an analog switch or the like is used. The switch 4 and the comparator 5 are examples of the gain switching circuit of the present invention.

An external circuit for selectively applying the first potential V ₁ and the second potential V ₂ to the terminal T ₁ is composed of the switch 6 and the volume VR ₁ . Voltage is applied to one input side (MP tape side) of switch 6.
V ₁ is connected, and the other input side (ME tape side) is connected to the voltage V ₂ given from the variable terminal of the volume connected between the + B power source and the ground. Here, the relationship between V ₁ and V ₂ is V ₁ <V ₂
It is configured to take values that do not overlap each other, such as.

In the above configuration, when the external switch 6 is operated to the MP tape side, the voltage V ₁ is discriminated as the first potential by the comparator 5 having the threshold value which is an intermediate value between the voltages V ₁ and V ₂ and the output is produced. It becomes "H", the switch 4 is switched to the amplifier 2 side, and the input V _IN is amplified by the fixed gain K. When operating the external switch 6 to the ME tape side,
The comparator 5 identifies it as the second potential, the output becomes "L", and the switch 4 is switched to the VCA3 'side. Since the control input of VCA3 'voltage V ₂ is connected, the gain is determined by the voltage V _2. That is, the gain can be variously changed depending on the value of the voltage V ₂ . Its gain V _OUT / V
_{The IN} is also designed as shown in FIG. 2 as an example in the case of this improved example. In addition to VCA3 ', amplifier 2 is also a VC
It goes without saying that the gain can be changed by A according to the first potential V ₁ .

Comparing this improved example with the above-mentioned embodiment of the present invention,
In the improved example of the figure, since the two amplifiers 2 and 3'are switched by the switch 4, either one of the amplifiers does not always operate, which results in waste in terms of cost and space. In the embodiment described above, since there is no switching of the amplifier by the switch and there is only one amplifier, the control circuit can be commonly used when the first potential and the second potential are applied,
There is an advantage that no waste occurs.

It should be noted that the present invention is not limited to the above-described embodiments, but can be variously applied and embodied in accordance with the gist of the present invention. In the above description, the gain switching corresponding to the MP tape / ME tape in the recording amplifier of the tape recorder has been described as an example, but it is needless to say that the present invention can be applied to general circuits that require the gain switching.

[Effects of the Invention] As is apparent from the above description, according to the present invention, a circuit configuration that conventionally requires two terminals for switching the gain of an amplifier and varying the gain of the amplifier is
It can be controlled by one terminal. Further, in this case, since the number of amplifiers is one and the gains of two systems are switched according to the first potential and the second potential without using a changeover switch or the like, the first potential and the second potential are The control circuit can be commonly used when the voltage is applied. For this reason, when it is made into an IC, the shape can be made small, the cost can be reduced, and the degree of freedom in IC design can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the principle of an embodiment of the present invention, FIG. 2 is a gain characteristic diagram of the embodiment, FIG. 3 is an actual circuit diagram of the embodiment, and FIG. Another gain characteristic diagram of the embodiment, FIG. 5 is a further gain characteristic diagram of the embodiment,
FIG. 6 is a circuit diagram having a gain characteristic of FIG. 5 showing a modified example of the embodiment, FIG. 7 is a block diagram showing an improved example of the conventional gain control circuit, and FIG. 8 is a conventional gain control circuit. It is a block diagram shown. 1 ... Integrated circuit, 2 ... Amplifier, 3 ... VCA (variable gain amplifier), 4 ... Switch, 5 ... Comparator, 7 ...
... Gain switching circuit, V ₁ ... first potential, V ₂ ... second potential.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Nakano 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (56) References JP-A-62-115905 (JP, A)

Claims (3)

(57) [Claims] 1. An integrated circuit having a variable gain amplifier, the gain of which is determined according to a current value of a variable current source, wherein a control electrode is connected to one terminal of the integrated circuit, and the control electrode is connected to the one terminal of the integrated circuit. First applied selectively from the outside
And a second potential input to the control electrode and a second transistor having a differential pair with the first transistor and a constant voltage source connected to the control electrode. A circuit, a third transistor connected to the controlled electrode of the first transistor of the input differential circuit, and a fourth transistor which forms a pair with the third transistor and controls a variable current source of the variable gain amplifier. A current mirror circuit including a transistor,
A switch circuit for selectively applying the fixed first potential and the adjustable second potential from the outside of the integrated circuit to the one terminal, and the one terminal to the first circuit. When a potential of 2 is applied, the gain of the variable gain amplifier is adjusted by controlling the variable current source via the current mirror circuit by adjusting the second potential. . 2. The gain control circuit according to claim 1, wherein the variable gain amplifier is a recording amplifier of a tape recorder. 3. The gain control circuit according to claim 1 or 2, wherein the gain switching circuit switches the gain in correspondence with a metal tape and a vapor deposition tape.