JPH0451094B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an improvement in a signal switching circuit configured with a fully feedback double-balanced differential amplifier circuit.

2. Description of the Related Art As shown in FIG. A differential circuit 6 is installed.

The first differential circuit 2 is composed of transistors 8 and 10, and the second differential circuit 4 is composed of transistors 1 and 10.
Further, the third differential circuit 6 is composed of transistors 16 and 18. The resistor 20 is a load resistor for the first and second differential circuits 2, 4, and each differential circuit 2, 4, 6 has a constant current source 2.
The operating current is given from 2.

A first signal is applied to the input terminal 24, a second signal is applied to the input terminal 26, and the transistors 16, 1
A switching signal is applied to the base of 8 from a control circuit (not shown), and the selected signal is taken out from the output terminal 28.

That is, when the base potential of the transistor 16 is higher than the base potential of the transistor 18, the first
Since an operating current flows through the differential circuit 2 , the first signal applied to the input terminal 24 is selected and appears at the output terminal 28 . Furthermore, when the base potential of the transistor 18 is higher than the base potential of the transistor 16, an operating current flows through the second differential circuit 4, so that the second signal applied to the input terminal 26 is selected and output to the output terminal 28. appears in

A in FIG. 4 is a switching signal applied to the base of transistor 18, and B in FIG. 4 is a switching signal applied to the base of transistor 16.
is a switching signal applied to the base of

Problems to be Solved by the Invention When performing this signal switching at high speed, the capacitance C _BC between the base and collector of transistors 16 and 18
As a result, an unnecessary switching pulse C ₀ is generated as a result of signal switching, as shown in C in FIG.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a signal switching circuit that suppresses the generation of unnecessary switching pulses in signal output due to such signal switching.

Means for Solving the Problems The signal switching circuit of the present invention includes first and second transistors 46 and 48 having a common emitter, and the second transistors have a common base and collector. , a first resistor 58 is connected between the base collector and the power supply side, a first signal to be selected is applied to the base of the first transistor, and a first signal to be selected is applied to the base of the second transistor. A first differential circuit 32 whose output is taken out from the collector side, and third and fourth transistors 50 and 52 having a common emitter, the third transistor having a common base and collector, and the third transistor having a common emitter. commonly connected to the base and collector of the second transistor, and
A second differential circuit 34, in which a second signal to be selected is applied to the base of the fourth transistor, and an output is taken out from the base/collector side of the third transistor, and the first differential circuit. The respective emitters of the corresponding fifth transistor 54 and the sixth transistor 56 corresponding to the second differential circuit are connected in common, and the fifth and sixth transistors are selectively turned on to their bases. a third differential circuit 36 to which a switching signal is applied, and a third differential circuit on the fifth transistor side between the fifth transistor of the third differential circuit and the first differential circuit; between the seventh transistor 38 connected via the second resistor 42 and having a constant DC voltage applied to its base, and the sixth transistor of the third differential circuit and the second differential circuit. an eighth transistor 4 which is connected to the sixth transistor side via a third resistor 44 and has a base applied with a constant DC voltage in common with the seventh transistor;
0.

A constant current source is installed between the first and second differential circuits and the third differential circuit, and a constant current is applied to the transistors constituting the third differential circuit.
In addition, since the resistor is connected in series to the capacitor between the base and collector of the transistor, changes in the current flowing through the capacitor are suppressed.

Embodiments Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of the signal switching circuit of the present invention.

A third differential circuit 36 is installed for the first and second differential circuits 32 and 34, and
In the current path between the differential circuits 32, 34 and the third differential circuit 36, transistors 38, 4 as seventh and eighth transistors as constant current sources are provided.
0 and resistors 42 and 44 are connected in series.

That is, the first differential circuit 32 has transistors 46 and 48 as first and second transistors having a common emitter, and the second differential circuit 34 has transistors 46 and 48 as third and fourth transistors having a common emitter. transistors 50 and 52, and the third differential circuit 36 has a transistor 5 as a fifth and sixth transistor having a common emitter.
4 and 56, respectively, and the transistor 5
Emitters 4 and 56 are connected to the ground point (GND). The resistor 58 as the first resistor is the first resistor.
and the load resistance of the second differential circuits 32 and 34.

Furthermore, at the bases of the transistors 38 and 40,
A bias is applied by a DC voltage applied from a voltage source 60, and in combination with resistors 42 and 44 as second and third resistors and transistors 54 and 56, a constant constant current is generated. .

The first and second signals are applied to the input terminals 62 and 64, and the transistors 54 and 56
A switching signal is applied to the base of the switch, and the selected signal is taken out from the output terminal 66.

Based on the above configuration, its operation will be explained with reference to FIG.

Transistor 46, 48 or transistor 5
If the current flowing through the transistors 0 and 52 is I, circuit conditions are set so that an operating current of 2I flows through the transistor 38 or the transistor 40.

In this case, the operating current flowing through transistors 46, 48 or transistors 50, 52 is set by transistors 38, 60, resistors 42, 44, and transistors 54, 56.

Now, if a voltage is applied to the base of the transistor 54 or the transistor 56 such that the transistor 54 or the transistor 56 becomes sufficiently conductive, the operating current 2I is as follows: 2I={V _B −V _BE −V _{CE( SAT)} }/R. Here, R is the resistance value of the resistor 42 or 44, V _BE is the emitter-base voltage of the transistor 38 or transistor 40,
V _CE(SAT) is the collector-emitter saturation voltage of transistor 54 or transistor 56.

Also, at this time, the resistance values of resistors 42 and 44
_R42 , _R44 are R= _R42 = _R44 , transistor 54,
56 collector-emitter saturation voltage V _CE(SAT)Q54 ,
V _CE(SAT)Q56 is V _CE(SAT) = V _CE(SAT)Q54 = V _CE(SAT)Q56
If so, the operating currents I flowing through the transistors 38 and 40 will be equal.

At this time, the base-emitter voltages V _BEQ38 and V _BEQ40 of the transistors 38 and 40 are V _BE =
It goes without saying that V _BEQ38 = V _BEQ40 .

Furthermore, when a voltage is applied to the base of the transistor 54 or the transistor 56 that makes the transistor 54 or the transistor 56 non-conductive, the collector-emitter of each transistor 54 and 56 is in an open state.
No operating current flows through transistor 38 or transistor 40.

When the switching signal pulse shown at A in FIG. 2 is applied to the base of transistor 56 and the switching signal pulse shown at B in FIG. The operating currents of the first and second differential circuits 32, 34 are alternately switched, and the first and second signals applied to the input terminals 62, 64 are switched to C in FIG. As shown, they are alternately selected and appear at output terminal 66.

In this case, _at C in FIG _.
Resistor 42 for the base-collector capacitance of 6,
44 are connected in series, changes in the current flowing through the capacitors are limited, and as a result, changes in the current flowing through the capacitances are suppressed to a negligible level compared to conventional circuits.

Furthermore, as is clear from a comparison with the conventional circuit shown in FIG. 3, since the transistors 54 and 56 are placed on the ground side, the collectors of the transistors 54 and 56 have a Since the saturation voltage is given to an extremely lower value than in the conventional circuit, the dynamic range of the signal can be expanded.

Effects of the Invention As explained above, according to the present invention, even when the signal switching speed is increased, the switching pulses accompanying the increased speed can be suppressed to an almost negligible level, and the dynamic range of the signal can be expanded. can be achieved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the signal switching circuit of the present invention, FIG. 2 is an explanatory diagram showing its operation, and FIG.
The figure is a circuit diagram showing a conventional signal switching circuit, and FIG. 4 is an explanatory diagram showing its operation. 32...First differential circuit, 34...Second differential circuit, 36...Third differential circuit, 38...Seventh transistor, 40...Eighth transistor, 4
2...Second resistance, 44...Third resistance, 46...
...First transistor, 48...Second transistor, 50...Third transistor, 52...Fourth transistor, 54...Fifth transistor, 56...Sixth transistor, 58...Third transistor 1
resistance.

Claims (1)

[Claims] 1. A first and a second transistor having a common emitter, the base and collector of the second transistor being common, and between the base and collector and the power supply side. A first resistor is connected, a first signal to be selected is applied to the base of the first transistor, and a first signal to be selected is applied to the base of the first transistor.
a first differential circuit whose output is taken out from the base-collector side of the transistor; and third and fourth transistors having a common emitter, the third transistor having a common base-collector, Commonly connected to the base and collector of the second transistor, a second signal to be selected is applied to the base of the fourth transistor, and an output is taken out from the base and collector of the third transistor. The emitters of a second differential circuit, a fifth transistor corresponding to the first differential circuit, and a sixth transistor corresponding to the second differential circuit are connected in common, and the base thereof is connected to the emitter of the fifth transistor corresponding to the first differential circuit. a third differential circuit to which a switching signal for selectively bringing the fifth and sixth transistors into conduction is applied; and the fifth transistor of the third differential circuit and the first differential circuit. a seventh transistor connected to the fifth transistor through a second resistor and having a constant DC voltage applied to its base; and the sixth transistor of the third differential circuit. and the second differential circuit, the eighth transistor is connected to the sixth transistor side via a third resistor, and a constant DC voltage is applied to the base in common with the seventh transistor. A signal switching circuit characterized by comprising: and.