JPH0429244B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application This invention relates to an amplifier, and particularly to an amplifier having a MIX (mixer) circuit function and other additional functions.

(B) Prior Art In general, audio equipment such as television receivers, radio receivers, and tape recorders are equipped with filters and MIX circuits that are controlled by VR (volume), for example. In conventional audio equipment, the filter and MIX circuit described above are completely independent circuits, and separate circuits are used.

(c) Problems to be solved by the invention In the conventional audio equipment described above, filters and
Since the MIX circuit is composed of completely independent circuits, the circuit configuration becomes complicated, which has the disadvantage of increasing the manufacturing cost of the entire device.

The present invention has been made in view of the above-mentioned problems, and provides an amplifier circuit that performs both a mixing function and a filter or electronic volume function, thereby reducing manufacturing costs of audio equipment, etc. The purpose is to achieve this goal.

(d) Means and operation for solving the problem The amplifier of the present invention has a first signal input terminal 7
, a second signal input terminal 9, and a pair of transistors TR1 and TR2, one of which is
A differential amplifier circuit 2 receives a signal from the first signal input terminal 7 at the base of TR1, and the base of the other transistor TR2 is connected to the signal output terminal, and derives a current flowing to the collector of the one transistor TR1. A first current inversion circuit 3, a second current inversion circuit 4 that derives the current flowing to the collector of the other transistor TR2, and a third current inversion circuit 5 connected to the second current inversion circuit.
The first and third current inversion circuits 3,
The series connection point of 5 is the other side transistor TR2.
an amplifier circuit 1 connected to the base of the amplifier circuit 1 to serve as a signal output terminal and also functions as a variable resistance circuit; and a capacitor C or a resistance element connected between the second signal input terminal 9 and the signal output terminal of the amplifier circuit 1. and a current control circuit 10 that changes the equivalent resistance value of the amplifier circuit 1 by controlling the current flowing through the differential amplifier circuit 2 according to the DC voltage applied to its input.

In this amplifier, when the DC voltage applied to the current control circuit is changed, the current flowing through the differential amplifier circuit changes accordingly, and the impedance of the amplifier circuit changes. Therefore, if the DC voltage applied to the current amplification circuit is adjusted appropriately while the first signal is input to the first signal input terminal and the second signal is input to the second signal input terminal, The output end has the first
A signal that is a mixture of the first signal and the second signal is output. In other words, this amplifier functions as a mixer.

Also, if no signal is input to the first signal input terminal and the voltage applied to the current control circuit is changed,
The impedance of the amplifier circuit changes. Therefore, the signal input to the second signal input terminal is output at a voltage division ratio determined by the impedance of the impedance element and the amplifier circuit connected to the input and output terminals. In this case, this amplifier functions as a filter for the signal input to the second signal input terminal.

(e) Examples The present invention will be explained in detail below using examples.

FIG. 1 is a circuit connection diagram of an amplifier showing an embodiment of the present invention. The amplifier of this embodiment is configured to operate not only as a MIX circuit but also as a filter.

In FIG. 1, 1 is an amplifier circuit, and this amplifier circuit 1 includes a differential amplifier circuit 2 consisting of transistors TR1 and TR2, a first current inverting circuit 3 consisting of transistors TR3 and TR4, and a transistor TR.
5 and TR6, and a third current inverting circuit 5 including transistors TR7 and TR8. Note that the first, second, and third current inversion circuits 3, 4, and 5 constitute an output circuit that derives the output current of the differential amplifier circuit 2. Of course, this amplifier circuit 1 itself is already a well-known circuit. As will be described later, this amplifier circuit 1 operates as a buffer amplifier or filter impedance with a 1:1 input:output ratio.

Reference numeral 6 denotes a buffer amplifier that derives the output signal V ₀ , and the output signal of the amplifier circuit 1 is input thereto. 7 is a signal input terminal to which the first input signal VinA is input, and is connected to the base of the transistor TR1 of the differential amplifier circuit 2.
8 is a terminal for applying bias voltage VB, and is connected to the base of transistor TR1 via resistor R1.

9 is a signal terminal to which the second input signal VinB is input, and is connected to the amplifier circuit 1 via the capacitor C.
is connected to the output terminal OP1 of. This capacitor C and the amplifier circuit 1 constitute a filter.

Reference numeral 10 denotes a current control circuit for controlling the current I of the differential amplifier circuit 2, which includes a transistor TR9 connected between the emitters of the transistors TR1 and TR2 of the differential amplifier circuit 2 and the reference voltage GND, and a resistor R2 connected in series. It consists of a circuit and an OP amplifier 11 that controls the current of the transistor TR9.

12 is a terminal for inputting the DC voltage VIN to the (+) input terminal of the OP amplifier 11 of the current control circuit 10. The output terminal of OP amplifier 11 is connected to the base of transistor TR9, and the (-) input terminal of OP amplifier 11 is connected to resistor R2 and transistor TR9.
is connected to the connection point of the emitter of the input terminal 12, and within a predetermined range of the DC voltage VIN applied to the input terminal 12, a current I flows in accordance with the DC voltage VIN. Note that 13 is a terminal to which a power supply voltage Vcc is applied, and 14 is an output terminal.

Next, the operation of the embodiment amplifier configured as above will be explained.

First, when functioning as a MIX circuit, the first
The first signal VinA (in Fig. 2) is connected to the signal input terminal 7 of the
(see VinA). This signal is for example
This is the signal from the MIC. Then, the second signal VinB (shown in Fig. 2) is input to the second signal input terminal 9.
(see VinB). This signal is, for example, a signal of background music. In such a state, that is, in a state where the signals VinA and VinB are input to the first and second signal input terminals 7 and 9, respectively, the level of the DC voltage VIN applied to the terminal 12 is 0.
(See t ₀ to _{t 1} of VIN in FIG. 2), the output signal is not derived to the OP amplifier 11, so the current I does not flow to the transistor TR9, and therefore the differential amplifier circuit 2 receives the signal. Signal applied to input terminal 7
Do not transmit VinA to the output terminal OP1 side at all. Therefore, the output signal V ₀ derived from the buffer amplifier 6 to the output terminal 14 is only a component of the signal VinB applied to the second signal input terminal 9 (from t ₅ to _{t 1} of V ₀ in FIG. reference).

Here, when the level of the DC voltage VIN applied to the input terminal 12 of the current control circuit 10 is increased (see t ₁ to _{t 2} of VIN in FIG. 2), the transistor TR 9 changes accordingly. Accordingly, the current I flowing through the differential amplifier circuit 2 also rises, and the input signal VinA applied to the first signal input terminal 7 is led out to the output terminal OP1 side. The output amplitude of this input signal VinA corresponds to the current I. Therefore, as the current I increases, the output of the signal VinA derived to the output terminal OP1 side also increases. On the other hand, an increase in the current I causes the equivalent impedance of the amplifier circuit 1 to decrease, and the signal VinB input to the second signal input terminal 9 is divided by the ratio of the impedance of the capacitor C and the amplifier circuit 1. A signal is delivered to the output OP1. Therefore, when the current I of the amplifier circuit 1 is at an appropriate value, the input signal is output to the output terminal 14.
Mixed output signal Vo of VinA and input signal VinB
(See _t1 to t2 of _V0 in FIG. ₂ ) is derived. When the DC voltage VIN input to the input signal 12 reaches a certain level, that is, when the current I increases to a certain extent, the equivalent impedance of the amplifier circuit 1 becomes very small, and the output of the signal VinB becomes almost 0, and the output The signal V ₀ will replace the input signal VinA from the input signal VinB (second
(see t ₂ in Figure V ₀ ). Therefore, if the DC voltage VIN input to the input terminal 12 is set to an appropriate level between t ₁ and _{t 2} in _FIG .
A mixture of VinA and VinB can be obtained.

Next, when functioning as a filter, input signal VinB is applied to input terminal 9, and no signal is input to input terminal 7. In this case, the amplifier circuit 1 is
It simply acts as an impedance element. That is, equivalently, an impedance Z is connected between the terminal OP1 and the reference potential GND. Then, when a DC voltage VIN (torso control signal) is applied to the input terminal 12 and changed, the current I changes in response to this change. In other words, the impedance Z of the amplifier circuit 1 changes. Therefore, the capacitor C and the circuit 1 whose impedance changes in response to changes in the DC voltage VIN operate as a filter circuit for the input signal VinB.

Note that in the amplifier of the above embodiment, the second input terminal 9
A capacitor C is connected between output terminal OP1 of amplifier circuit 1 and output terminal OP1 of amplifier circuit 1.
In this example, a resistor R may be connected in place of the capacitor C. This makes it possible to obtain an amplifier with an electronic volume function added to the MIX circuit. In this amplifier, signal input terminal 7,
By applying input signals VinA and VinB to input terminals 9 and 9 and applying an appropriate DC voltage VIN to the input terminal 12 of the current control circuit 10, it operates as a MIX circuit in the same way as the amplifier shown in FIG.
applying the signal to be adjusted to the second signal input terminal 9;
Furthermore, if the impedance Z of the circuit 1 is changed by changing the DC voltage VIN applied to the input terminal 12 of the current control circuit 10, the resistance R and the impedance Z
By changing the division ratio of , the signal level delivered to the output terminal 14 can be changed. In other words, it operates as an electronic volume.

(F) Effects of the Invention According to the present invention, an amplifier circuit including a differential amplifier circuit and first, second, and third current inverting circuits for deriving the current output of the differential amplifier circuit can be integrated into a MIX circuit. Since it can also be used as an impedance element as a buffer amplifier, a filter, or an electronic volume, it is possible to easily configure an amplifier with a filter function or an electronic volume function in a MIX circuit, thereby reducing manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a circuit connection diagram of an amplifier showing an embodiment of the present invention, and FIG. 2 is a signal waveform diagram for explaining the operation of the amplifier. 2... Differential amplifier circuit, 3, 4, 5... Current inversion circuit, 7... First signal input terminal, 9... Second signal input terminal, 10... Current control circuit, C... Capacitor .

Claims (1)

[Claims] 1. Consisting of a first signal input terminal 7, a second signal input terminal 9, and a pair of transistors TR1, TR2, the first signal input terminal 7 is connected to the base of one transistor TR1. a differential amplifier circuit 2 in which the base of the other transistor TR2 is connected to the signal output terminal;
current inversion circuit 3, the other transistor TR
a second current inverting circuit 4 that derives a current flowing through the collector of the second current inverting circuit 2; and a third current inverting circuit 5 connected to the second current inverting circuit; 3 and 5 are connected to the base of the other side transistor TR2 to become a signal output terminal, and the amplifier circuit 1 also functions as a variable resistance circuit; the second signal input terminal 9 and the amplifier circuit 1; The equivalent resistance value of the amplifier circuit 1 is changed by controlling the current flowing through the differential amplifier circuit 2 according to the DC voltage applied to the input and the capacitor C connected between the signal output terminals. An amplifier comprising: a current control circuit 10 that performs a mixing function, a filter function, or an electronic volume function depending on the input level to the current control circuit 10.