JP2001308658A - Balanced amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a balanced amplifier circuit having a low input impedance using a simple constitution. SOLUTION: The balanced amplifier circuit comprises a pair of transistors 1, 2; a pair of load resistors 5, 6, both of which are connected to the collectors of the transistors 1, 2; and a potentiometer 7, which has at least two voltage- dividing elements 7a, 7b, where the tap voltage of the potentiometer 7 is applied to the bases of the transistors 1, 2 as a common bias voltage, a signals is input between the emitters of the transistors 1, 2 for which the signals become as a pair of signals of mutually opposite phase, and the collectors of the transistors 1, 2 are set as the output terminals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a balanced amplifier circuit suitable as a high-frequency amplifier circuit for a television tuner or the like.

[0002]

2. Description of the Related Art As shown in FIG. 1, a conventional balanced amplifying circuit has two transistors 21 and 22, both emitters of which are connected to a constant current source 23, and each collector has a load resistance 24. , 25 are connected, and the load resistance 24,
The power supply voltage is supplied to each collector via the reference numeral 25. A balanced signal is input to the bases of the transistors 21 and 22, and the amplified signal is output from two collectors.

When a balanced signal is input to the base, the increasing and decreasing directions of the emitter current of the transistor 21 and the increasing and decreasing directions of the emitter current of the transistor 22 are opposite to each other. As a result, the potentials of the two emitters fluctuate. do not do.
As a result, common emitter type (common emitter type)
Constitutes a balanced input / balanced output type balanced amplifier circuit.

[0004]

The above-mentioned balanced amplifying circuit is of a common emitter type and therefore has a relatively high input impedance. When used as a high-frequency amplifying circuit for a television tuner or the like, an ordinary design impedance is required. (50 ohms or 75 ohms), and was connected to an antenna or another circuit via a tuning circuit having an impedance conversion function, for example.

Although it is possible to lower the input impedance by providing a negative feedback circuit in parallel with the balanced amplifier circuit, the use of this configuration deteriorates the transfer characteristics in the reverse direction (from the output side to the input side). It is not possible to construct a direct conversion type television tuner.

Further, since the level of an input signal is high when the input impedance is high, even if the signal level on the signal source side is the same, the level of distortion generated becomes larger than that of an amplifier circuit having a low input impedance. There are drawbacks.

Accordingly, an object of the present invention is to realize a balanced amplifier circuit having a low input impedance with a simple configuration.

[0008]

According to the present invention, there is provided, as a means for solving the above problems, two transistors, a load resistor respectively connected to the collectors of the two transistors, and at least two voltage dividers connected in series. A voltage dividing circuit having an element and outputting a divided voltage to a connection point of the two voltage dividing elements, applying the divided voltage as a common bias voltage to the bases of the two transistors, Signals having opposite phases were input between the emitters of the transistors, and the collectors of the two transistors were used as output terminals.

In addition, the semiconductor device has two transistors, a load resistor respectively connected to the collectors of the two transistors, and at least two voltage-dividing elements connected in series. A voltage dividing circuit for outputting a voltage, applying the divided voltage as a common bias voltage to the bases of the two transistors, grounding one emitter of the two transistors at high frequency, and A signal was input to the emitter, and the collectors of the two transistors were used as output terminals.

A negative feedback resistor is connected between the connection point and each base of the two transistors.

Further, both of the two voltage dividing elements are constituted by resistance elements.

Further, one of the two voltage dividing elements is constituted by a resistance element, and the other is constituted by a diode, and a forward current is applied to the diode.

Further, a plurality of the diodes are used.

[0014]

1 to 3 are circuit diagrams showing the configuration of a balanced amplifier circuit according to the present invention. First, FIG. 1 shows a first embodiment, in which the emitters of two transistors 1 and 2 are grounded via emitter resistors 3 and 4, respectively, and the collectors are connected to a power supply via load resistors 5 and 6, respectively. Connected to positive electrode. The bases are connected to each other and to a connection point of two voltage-dividing elements connected in series, for example, the voltage-dividing resistance elements 7a and 7b.
The two voltage-dividing resistance elements 7a and 7b form a voltage-dividing circuit 7. A voltage of a power supply is applied to both ends of the voltage-dividing circuit 7, and a divided voltage is output between the voltage-dividing resistance elements 7a and 7b. And
Each emitter is an input terminal, and each collector is an output terminal.

When balanced signals having phases opposite to each other are input to the two emitters, the sum of the base currents flowing through the respective bases is always constant.
The potential of the connection point between a and 7b is also constant, and each base becomes a virtual ground point in terms of high frequency. Therefore, even if the base is not connected to the ground by a high-frequency grounding means such as a bypass capacitor, a balanced amplifier of a common base type (grounded base type) and a balanced input / balanced output type is formed, which facilitates the integration into an integrated circuit. Become.

In general, a common-base type amplifier circuit has an input impedance of several tens of ohms.
Even when connected to an ohmic circuit, impedance matching can be almost obtained.

FIG. 2 shows a second embodiment. Here, the emitter of one transistor 2 is grounded at a high frequency by a bypass capacitor 8. The other configuration is the same as the configuration shown in FIG.
Then, a signal is input only to the emitter of the transistor 1. Also in this case, the two transistors 1, 2
Of the two transistors 1 and 2, balanced signals are output from the respective collectors of the two transistors 1 and 2. Even in this case, the bases of the two transistors are virtual ground points. Therefore, an unbalanced input / balanced output type balanced amplifier circuit is configured.

Since a 75-ohm antenna is generally of an unbalanced type, it is suitable for using a balanced amplifier circuit having an unbalanced input as a high-frequency amplifier circuit.

FIG. 3 is a modification of FIG. 2, and shows a configuration in which resistors 9 and 10 for negative feedback are respectively connected between the connection points of the voltage dividing resistance elements 7a and 7b and each base in FIG. Other configurations are the same as those in FIG. In this configuration, negative feedback is applied by the negative feedback resistors 9 and 10, and the gain is slightly reduced, but the distortion characteristics are improved. It should be noted that a resistor for negative feedback can be similarly provided in the configuration of FIG.

FIGS. 4 and 5 show another configuration of the voltage dividing circuit 7, in which one voltage dividing element is constituted by a resistor element 7a or 7b and the other voltage dividing element is constituted by a plurality of diodes 7c. I have. The diode 7c is provided on the positive side (see FIG. 4) or the ground side (see FIG. 5) of the power supply, and a forward current flows. In this case, the diode 7c
Are almost constant without being affected by the fluctuation of the power supply voltage, so that the base bias voltages of the two transistors 1 and 2 are stabilized. Integration into an integrated circuit is also easy. Also, by using a plurality of diodes 7c, the value of the base bias voltage can be set appropriately.

[0021]

As described above, the balanced amplifying circuit according to the present invention has two transistors, load resistors respectively connected to the collectors of the two transistors, and at least two voltage dividing elements connected in series. A voltage dividing circuit for outputting a divided voltage at a connection point of the two voltage dividing elements, applying the divided voltage as a common bias voltage to the bases of the two transistors, and applying an anti-phase between the emitters of the two transistors to each other , And the collectors of the two transistors are used as output terminals, so that the bases of the two transistors are virtually grounded, and a balanced input / balanced output type balanced amplifier circuit with low input impedance can be easily configured. . Further, integration into an integrated circuit is facilitated.

Further, two transistors, load resistors respectively connected to the collectors of the two transistors,
A voltage dividing circuit having at least two voltage dividing elements connected in series and outputting a divided voltage at a connection point of the two voltage dividing elements, and using the divided voltage as a common bias voltage at a base of the two transistors. Since one emitter of the two transistors is grounded at a high frequency, a signal is input to the other emitter, and the collectors of the two transistors are output terminals, the bases of the two transistors are virtually grounded. Thus, an unbalanced input / balanced output type balanced amplifier circuit having a low input impedance can be easily configured.
Further, integration into an integrated circuit is also facilitated.

Also, since a negative feedback resistor is connected between the connection point of the two voltage dividing elements and each base of the two transistors, a balanced amplifier circuit with less distortion can be constructed.

Further, since both of the two voltage dividing elements are constituted by resistance elements, the voltage dividing circuit can be easily constituted.

Since one of the two voltage-dividing elements is constituted by a resistance element and the other is constituted by a diode, and a forward current is passed through the diode, the divided voltage is stabilized.

Also, since a plurality of diodes are used, the base bias voltage of the two transistors can be set appropriately.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment in a balanced amplifier circuit of the present invention.

FIG. 2 is a circuit diagram illustrating a configuration of a balanced amplifier circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing another configuration of the balanced amplifier circuit of the present invention.

FIG. 4 is a circuit diagram showing another configuration of the voltage dividing circuit used in the balanced amplifier circuit of the present invention.

FIG. 5 is a circuit diagram showing still another configuration of the voltage dividing circuit used in the balanced amplifier circuit of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a conventional balanced amplifier circuit.

[Explanation of symbols]

 1, 2 Transistor 3, 4 Emitter resistance 5, 6 Load resistance 7 Divider circuit 7a, 7b Divider resistive element (divider element) 7c Divider diode (divider element) 8 Bypass capacitor 9, 10 Negative feedback resistor

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) KA12 MA13 MA21 MN01 NN06 SA08 5J092 AA01 AA12 AA22 CA21 CA71 CA91 FA00 HA02 HA19 HA25 HA29 KA00 KA05 KA12 MA13 MA21 SA08

Claims (6)

[Claims] 1. Two transistors, load resistors respectively connected to the collectors of the two transistors,
A voltage dividing circuit having at least two voltage dividing elements connected in series and outputting a divided voltage to a connection point of the two voltage dividing elements, wherein the divided transistors are used as a common bias voltage for the two transistors. Wherein a signal having an opposite phase is input between the emitters of the two transistors, and the collectors of the two transistors are used as output terminals. 2. Two transistors, load resistors respectively connected to the collectors of the two transistors,
A voltage dividing circuit having at least two voltage dividing elements connected in series and outputting a divided voltage to a connection point of the two voltage dividing elements, wherein the divided transistors are used as a common bias voltage for the two transistors. Wherein one emitter of the two transistors is grounded at a high frequency, a signal is input to the other emitter, and the collectors of the two transistors are output terminals. circuit. 3. The balanced amplifier circuit according to claim 1, wherein a negative feedback resistor is connected between the connection point and each base of the two transistors. 4. The balanced amplifying circuit according to claim 1, wherein both of said two voltage dividing elements are constituted by resistance elements. 5. The device according to claim 1, wherein one of the two voltage dividing elements is constituted by a resistance element, and the other is constituted by a diode, and a forward current is caused to flow through the diode. A balanced amplifier circuit as described. 6. The balanced amplifying circuit according to claim 5, wherein a plurality of said diodes are used.