JPH0257368B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mixing circuit used in audio and video equipment, and relates to a mixing circuit used for mixing two types of signals.

[Conventional technology]

FIG. 3 shows a conventional mixing circuit of this type. In the figure, A and C are input terminals, O is an output terminal, V is a power supply terminal, G is a ground terminal, 1,
2, 4, 10, 9, 7 are emitter follower circuit bias resistors, 3, 8 are emitter follower transistors, d, e are output DC breaking capacities, 5, 6 are mixing resistors, emitter follower type with voltage gain of 1. A mixing amplifier is composed of two amplifiers.

Next, the operation will be explained.

By configuring an emitter follower amplifier with transistors 3 and 8, an amplifier with high input-low output impedance and voltage gain of 1 can be obtained. Now, the signals applied from the input terminals A and C are taken out almost unchanged to the emitters of the transistors 3 and 8, respectively. Here, the signal taken out from the connection point O between the resistors 5 and 6 is obtained from the input signals VA and Vc as follows: Vo=1/2 (VA+Vc). However, it is assumed that the values of resistances 5 and 6 are equal.

[Problem that the invention seeks to solve]

Conventional mixing circuits are configured as described above, and when configured with discrete emitter follower transistors, the output DC voltage of the emitter follower type transistor fluctuates depending on variations in the base-emitter voltage and temperature characteristics. , a DC voltage difference occurs between the right channels, which inevitably requires DC breaking capacity as shown in d and e in the figure, resulting in disadvantages such as an increase in the cost of the audio set and changes (variations) in the electrical characteristics.

[Means for solving problems]

The mixing circuit according to the present invention has a circuit configuration in which the device is provided with two differential amplifiers each consisting of two differential transistors and an emitter follower circuit, and the outputs of both amplifiers are taken out through mixing resistors, respectively. A semiconductor integrated circuit is constructed in which corresponding circuit element constants are made equal between the right channels.

[Effect]

In this invention, since circuit elements having the same constants corresponding to the left and right channels are formed in the semiconductor integrated circuit, the electrical characteristics and temperature characteristics of both channels are the same, and the direct current between the two channels is The voltage difference disappears.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a mixing circuit according to an embodiment of the present invention. In the figure, Q5 and Q6 are differential transistors whose collectors are connected to the power supply V, and 30 is an output from the common emitter of the differential transistors Q5 and Q6. It is an emitsuta follower circuit that takes out the
This is composed of transistors Q8 and Q7. And the differential transistors Q5, Q6,
A differential emitter follower circuit (differential amplifier) 20 is configured by the emitter follower circuit 30,
Similarly, differential transistors Q15 and Q16
A differential emitter follower circuit (differential amplifier) 40 is also constituted by an emitter follower circuit 50 consisting of transistors Q12 and Q11. The outputs of the differential emitter follower circuits 20 and 40 are connected to the output terminal O via resistors 5 and 6, respectively. Also, transistors Q1 and Q
2, Q3, Q9, Q10, Q14, resistors R1 to R
5, R7 to R11, R13 are bias elements of the differential emitter follower circuits 20, 40, respectively, and the transistors Q1, R13, which have the same size,
Q2, Q3, Q9, Q10, Q14 and the above resistors R1 to R5, R7 to R11, R1 with equal resistance values
3 constitutes a stabilized power supply 60 having low impedance characteristics.

Further, the resistors 6 and R12 are resistors that determine the input impedance of each of the differential emitter follower circuits 20 and 40, and the bases of the transistors Q5 and Q16 of the differential emitter follower circuits 20 and 40 are connected through the resistors R6 and R12, respectively. The bases of the transistors Q5 and Q16 are connected to the stabilized power supply 60, and the bases of the transistors Q5 and Q16 are respectively connected to the capacitors a and
It is connected to input terminals A and C via c. In this embodiment, the circuit constants of the components of the differential amplifiers 20 and 40 and the resistance values of the mixing resistors 5 and 6 are the same between the left and right channels.

Next, the operation will be explained.

The input bias voltage VB of the differential emitter follower circuits 20 and 40 can be determined from the power supply voltage V by VB=V-2VBE/(R4+R5)×R5+2VBE. However, this formula is based on the resistance R
This is true when considering that the voltage across both ends is approximately VBE. Therefore, from the input bias voltage VB, the output DC voltage Vo of the differential emitter follower circuits 20 and 40 becomes Vo=VB-VBE, that is, Vo=V-2VBE/R4+R5×R5+VBE [V].

Now, when an input signal is applied to terminal A, the input signal is transmitted from transistor Q5 to the emitter of transistor Q8, and output VA is obtained from the emitter of transistor Q7. At this time transistor Q6
Since the base of is grounded, the transistor Q5
only works. Similarly, when an input signal is applied to terminal C, the input signal is applied to transistor Q16.
It passes through the emitter of transistor Q12 and is transmitted to the emitter of transistor Q12, and output Vc is obtained from the emitter of transistor Q11.

The signals VA and Vc obtained in this way are mixed by the resistors 5 and 6 having the same resistance value, as in the conventional example, and the signal Vo=(VA
+Vc)/2 is obtained as the output signal of this mixing circuit.

In this way, according to this embodiment, a semiconductor integrated circuit is constructed in which the constants of the corresponding circuit elements are equal in the left and right channels, so that the electrical characteristics including the temperature characteristics are equal. Become,
This eliminates the need for a capacitor for cutting the output DC, and has the advantage of providing better balance between the left and right sides.

Note that in the above embodiment, transistors Q6 and Q1
I explained that the base of 5 is grounded,
As shown in FIG. 2, transistors Q6 and Q15
By controlling , the differential emitter follower amplifier can be used as a switch circuit.

The basic operation of this circuit is the same as that of the above embodiment, so the explanation will be omitted, but the transistor Q6,
By selecting whether the base voltage of Q15 is high or low using switches S1 and S2, it can be used as a mixing circuit or output only one channel signal.

〔Effect of the invention〕

As described above, according to the mixing circuit according to the present invention, two differential amplifiers each consisting of two differential transistors and an emitter follower circuit are provided, and the circuit configuration in which the output is taken out via a resistor is shown on the left. Since the circuit constants of the corresponding components in the right channel are made equal and the circuit constants are made of semiconductor integrated circuits, there is no need for a DC interrupting capacity, which has the effect of reducing costs.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a mixing circuit according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing another embodiment of the invention, and Fig. 3 is a circuit diagram showing an embodiment of a conventional mixing circuit. It is. 20, 40...Differential amplifier, Q5, Q6 and Q
15, Q16...Differential transistor, Q7, Q8
and Q11, Q12... transistors, 5, 6...
...Mixing resistor, A, C...Input terminal, O...
...output terminal, R6, R12...resistance, 30,50
... Emitsuta follower circuit, 60 ... Stabilized power supply with low impedance characteristics.

Claims (1)

[Claims] 1. The emitters are directly connected, each collector is connected to a power supply, and one base is connected to a stabilized power supply having low impedance characteristics via a resistor, and an input signal to be mixed is applied. Ta2
It is equipped with two differential amplifiers each having two differential transistors and an emitter follower circuit that extracts the output from the common emitter of the two differential transistors, and outputs the output to the output of each differential amplifier via a mixing resistor. A mixing circuit characterized in that terminals are connected to each other, and the mixing outputs of the two amplifiers are taken out to the output terminals. 2. The mixing circuit according to claim 1, wherein the constants of corresponding circuit elements are equal between the left and right channels, and the entire circuit is made of a semiconductor integrated circuit.