JPS59152727A - Signal switching circuit - Google Patents

Abstract

PURPOSE:To obtain a dynamic range sufficient to drive by a low voltage by providing respectively a signal transmission circuit using an inverted Darlington connection between the 1st and 2nd input circuits and two constant current sources. CONSTITUTION:A signal inputted from input terminals 6 and 20 is fed to cross coupling type differential switching circuits 11, 12, 13, 14 by signal transmission circuits 33, 35, 36, 37; 34, 39, 40, 41, 42 of the 1st and 2nd inverted Darlington connection, and when a high and a low level voltage are applied respectively to terminals 24, 25 of transistors (TRs) 26, 27, TRs 11, 14 are activated and TRs 12, 13 are cut off, and when the signal inputted from the input terminal 20 results in applying a low and a high level voltage to the terminals 24, 25, the signal inputted from the input terminal 6 is outputted to an output terminal 22.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal switching circuit particularly suitable for use in integrated circuits driven at low voltage.

(Prior Art) As a conventional signal switching circuit, there is a circuit as shown in FIG. 1, for example.

In the figure, transistors 11, 12, 13, and 14 constitute a cross-coupled differential switching circuit, and resistors 1, 2, and 4°5
and transistor 6 is transistor 11-140 base V
C - A pillow that constitutes a bias circuit that supplies a bias voltage. Resistor 8, 9,) Ranjistaf, 10 foot current source 2
9 and the input terminal 6 are connected to the first differential amplifier, resistor 17.18, ) transistor 16.19, constant current source 60. A second differential amplifier is configured with the input terminal 2o.

The resistor 15 is a common load for the first and second differential amplifiers, and the signal is passed through the transistors 21. The signal is outputted to the output terminal 22 via an emitter follower made up of a resistor 23. Transistors 26, 27 and resistor 28 are connected to output terminal 22
This is a circuit for switching the signal output to the

Next, the operation of the above-mentioned conventional circuit will be explained. High level II pressure is applied to terminal 24 and low level II pressure is applied to terminal 25.
When transistor 26 is active and transistor 27 is cut off, transistors 11 and 14 are active and transistors 12 and 16 are cut off. Then, the signal input from terminal 2o is transmitted to output terminal 2o.
2 will appear.

During backwashing, when a low level voltage is applied to the terminal 24 and a high level voltage is applied to the terminal 25, when the transistor 26 is in the cutoff state and the transistor 27 is in the active state, the transistors 11 and 14 are in the cutoff state and the transistor 12 is in the cutoff state.
．． 13 becomes active. Then, the signal inputted from the terminal 6 is outputted to the output terminal 22. Also, constant current source 2
If the currents flowing through 9.30 are equal, the DC voltage at the output terminal 22 does not change during signal switching, and the signal can be switched.

However, in such a conventional circuit, the constant current source 29
Alternatively, it is necessary to stack six transistors including 30 transistors. Therefore, if it is attempted to maintain a reverse biased state between the base and collector of each transistor, the dynamic range at the output terminal 22 will be extremely difficult to maintain when operating at a low voltage of about 5V. The purpose is to provide a signal switching circuit that can obtain a sufficient dynamic range even when driven at a low voltage of about 5V.

t) A feature of the present invention is that in a signal switching circuit having a first input circuit, a second input circuit, and a cross-coupled differential switching circuit driven by two constant current sources, By providing a signal transmission circuit using an inverted Darlington connection between the first and second input circuits and the two constant current sources, the number of transistors is reduced to two stages, thereby reducing the number of transistors at the output end. The key point is that the dynamic range has been expanded so that sufficient performance can be obtained even when driven at a low voltage of about 5V.

EXAMPLES Below, the present invention will be explained with reference to Examples. FIG. 2 shows a circuit diagram of an embodiment of the present invention.

In the figure, filters 1 and 32 are constant current sources connected to a cross-coupled differential switching circuit composed of transistors 11 to 14. Also, resistance 33. Transistor 35, s6. resistance 3
7 and a constant voltage source, 38, a resistor 8I9, a transistor 7', 10. This is a first signal transmission circuit that connects a first differential amplifier made up of a constant current source 29 and an input terminal 6, and a cross-coupled differential switching circuit made up of transistors 11 to 14. Resistance 34. The transistors 39 and 40, the resistor 41, and the constant voltage source 42 have a resistor of 17.1B, )
Ransistor 16.19.

This is a second signal transmission circuit that connects a second differential amplifier consisting of a constant current source 30 and an input terminal 20 to the cross-coupled differential switching circuit. Note that the same reference numerals in FIG. 2 as in FIG. 1 indicate the same components as in FIG. 1.

According to this embodiment having such a configuration, the resistors 33 and 34
Since a current according to the input signal flows through the input terminals 6 and 20, the signals inputted from the input terminals 6 and 20 are transferred to the cross-coupled differential switching circuit by the above-mentioned first and second inverted Darlington connection signal transmission circuits. The signal current is transmitted to the circuit.

Therefore, as in the example of the conventional circuit shown in FIG. 1, high level and low level ! When pressure is applied, transistors 11 and 14 are activated and transistors 12 and 14 are activated.
13 is in the cutoff state, and the signal input from the input terminal 20 is output to the output terminal 22. 1.Conversely, when a low level voltage is applied to the terminal 24 and a high level voltage is applied to the terminal 25, the transistor i is 1.
1 and 14 are in a cut-off state, transistors 12 and 13 are in an active state, and the signal input from the input terminal 6 is output to the output terminal 22.

In the circuit of this embodiment, whereas the conventional circuit shown in FIG. 1 requires stacking transistors in six stages, only two stages are necessary. Therefore, there is an advantage that a sufficient dynamic range can be ensured even during operation at a low voltage of about 5V.

FIG. 3 more specifically represents the circuit diagram of FIG. 2, and shows one circuit diagram.

In the figure, a circuit surrounded by a dotted line consisting of resistors 43, 46, transistors 44 and 45 indicates the constant voltage source 38 and 42 of the circuit in FIG. In this circuit, the constant voltage source surrounded by the dotted line serves as a common power source for the first and second signal transmission circuits. transistor 5
3 and the resistor 49 constitute a constant current source 29, and the transistor 54 and the resistor 50 constitute a constant current source 30. Further, the transistor 51 and the resistor 47 constitute a constant current source 31, and the transistor 52 and the resistor 48 constitute a constant current source 62. In addition,
Reference numerals other than those mentioned above indicate the same items as in FIG. 2.

Now, in the circuit of Fig. 3, transistors 51 and 52
bareness of transistor 53. ．． 54 paired transistors 35, 39 paired transistors and transistors 36.40
In addition, the resistance ratio is 47.48, the resistance ratio is 49.50, and the resistance is 4.

By setting the resistance ratio of 33.3'4 and the resistance ratio of resistor 37.41 to approximately 1, in addition to the effect that a sufficient dynamic range can be obtained even during low voltage operation of about 5V, it is possible to obtain a sufficient dynamic range when switching signals. The DC offset of the output terminal 22 can be made as small as g compared to the conventional example shown in FIG.

That is, the currents flowing through the constant current sources 31 and 32 are 'l + '2, respectively, and the currents flowing through the constant current sources 61 and 61 from the first signal transmission circuit are
The current flowing into 'Sr from the second signal transmission circuit to the constant
[If the current flowing into one side and one source 32 is B, a high voltage is applied to the terminal 24 connected to the base of the transistor 260, and a low voltage is applied to the terminal 25 connected to the base of the transistor 250, and the transistors 11 and 14 active state,
When the transistors 12 and 13 are in the cut-on state, a current of 12-i4 flows through the resistor 15. On the other hand, a low signal is connected to the terminal 24 connected to the base of the transistor 26.
When a high voltage is applied to the terminal 25 connected to the base of the transistor 250, and the transistor 12.13 is activated and the transistor 11.14 is cut off, a current of i, -i flows through the resistor 15. flows.

By the way, as mentioned above, if the circuit is made so that the transistors are sufficiently paired and the resistance ratio of the resistors is gl, then the currents t1 and t2 are y When there is no signal to the input terminals 6 and 2D, the currents z3 and t4 become equal to g.

Therefore, the current 12L4 flowing through the resistor 15 when the transistor 11.14 is on and there is no signal, and the current 12L4 flowing through the resistor 15 when the transistor 12.13 is on and there is no signal.
The current i, −i, flowing through the output terminal 5 is equal to g, and as mentioned above, the current i, −i, flowing through the output terminal 22 at the time of signal switching is
The offset will be smaller.

4! .

According to the signal switching circuit of the present invention, a sufficient dynamic range can be obtained even when driven at a low voltage of about 5V.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional signal switching circuit, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a circuit diagram showing FIG. 2 in more detail. 6.20・・・・・・・・・・・・・・・−・Input terminal 2
2・・・・・・・・・・・・・・・・・・・・・Output terminal 38.42・・・・・・・・・・・・・・・・・・
Constant voltage source 29.30, 31.32...Constant current source Patent attorney Akio Takahashi Ogi 1 l Do 3 Figure

Claims (1)

[Claims] (1) In a signal switching circuit having a first input circuit, a second input circuit, and a cross-coupled differential switching circuit driven by two constant current sources, the first and second input circuits 7. An inverted Darlington connection is made between each of the two constant current sources and the two constant current sources. : npn, pnp)
A signal switching circuit comprising: a signal transmission circuit including a transistor;