JPH0817295B2 - Level shift circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor electronic circuit, and more particularly to a level shift circuit capable of expanding the operable temperature range of the circuit.

[Conventional technology]

In general, when a semiconductor electronic circuit is integrated or when signal transmission up to direct current is possible, a direct connection method without a capacitor is often used. However, when amplifier circuits and the like are connected in multiple stages, the DC level of the signal tends to rapidly increase toward the positive or negative supply voltage. By this,
The amplitude of the output signal and its linearity will be limited.

Therefore, conventionally, a method has been adopted in which a level shift circuit is inserted between stages to shift the DC level of the output signal of the circuit of the previous stage and transmit it to the circuit of the subsequent stage.

FIG. 4 shows an example of a conventional level shift circuit. If the transistors 8 and 9 have the same characteristics, the input voltage V _IN applied to the input terminal 4 and the output terminal 5
The level shift amount, which is the difference between the output voltage V _OUT and the output voltage V _OUT , is expressed by the following equation 1.

However, in the above equation, V _BE represents the base-emitter voltage of the transistor. Since the output impedance of the transistor 9 is generally much larger than the value R _L of the level shift resistor 2, the AC voltage gain of the circuit of FIG. 2 is close to unity.

[Problems to be solved by the invention]

The prior art described above does not consider the temperature drift of the level shift amount, and has a problem that the level shift circuit adds a temperature drift exceeding the necessary range to the DC level of the signal.

FIG. 5 shows an example of a differential amplifier circuit using a level shift circuit. In FIG. 5, transistor 1 and
By using a pair of level shift circuits composed of 10, level shift resistors 2 and 12 and bias current sources 9 and 13, it is possible to prevent the temperature drift from being added to the differential signal. However, the utilization factor of the power supply voltage V _CC1 of the differential amplifier circuit formed by the transistors 15 and 16 is limited by the temperature drift applied to the DC level of the signal.
For example, even if the collector currents I _C2 of the transistors 15 and 16 are set as the curves 22 and 23 of FIG. 6 at room temperature, respectively, the broken curves 24 and
Tends to 25. The above problem becomes a factor that limits the operable temperature range of the circuit when the power supply voltage is not sufficiently high compared to the signal amplitude or when a large number of circuits having various temperature drifts are connected.

An object of the present invention is to provide a level shift circuit capable of expanding the operable temperature range of the electronic circuit by arbitrarily setting the temperature drift of the level shift amount.

[Means for solving problems]

The first purpose is to have a base connected to a signal source and a collector biased through a low impedance.
One end of a level shift resistor is connected to the emitter of the transistor, and a current source is connected to the other end of the resistor, and an input signal input from the signal source via the base is level-shifted to perform the level shift. In the level shift circuit which takes out as an output signal from the other end of the resistor, the value of the current flowing through the level shift resistor is determined by the combination of the second transistor having a known temperature drift amount and the resistance element as the current source. This is achieved by using a current source circuit.

[Action]

The emitter follower circuit including a transistor whose base is connected to the signal source operates as a buffer that prevents the level shift circuit from becoming a load in the preceding stage.

A resistance for level shift biased by a current source capable of having an arbitrary temperature drift and current value operates as a voltage source having an arbitrary temperature drift and voltage value. By setting the level shift amount by the voltage source, the temperature drift of the level shift circuit can be set arbitrarily.

Embodiments Embodiments of the present invention will be described below with reference to the drawings, but before that, the principle of the present invention will be described.

FIG. 7 is a circuit diagram showing the principle of the present invention. The level shift amount in FIG. 7 can be expressed by the following equation 2.

V _IN −V _OUT = V _BE + R _{LIB (T)} (Equation 2) When actually designing the circuit, consider the parasitic capacitance at the output terminal 5 and the bias current that can flow in the transistor 1, and Determine _L and I _{B (T)} . Then, when the temperature coefficient of the input voltage V _IN is .theta.V _IN / .theta.T, if you want to the temperature coefficient of the output voltage V _OUT to .theta.V _out / .theta.T it may be caused to satisfy the relationship of the following equation 3.

Therefore, in order to suppress the temperature drift of the level shift amount to zero, it is necessary to use the bias current source 3 having the characteristic of the following Expression 4.

The circuit designer can optimize the operable temperature range of the circuit by appropriately using the relationship shown in the above expression 3.

It is needless to say that the present invention can be realized by inverting the polarity of the bias current source 3 even if the transistor 1 is of PNP type in FIG. Also,
It is also possible to replace the transistor 1 with a FET.

Further, when the impedance of the input signal source is sufficiently small, the transistor 1 in FIG. 7 is deleted, and the terminal other than the output terminal side of the level shift resistor 2 is
It can be directly used as the input terminal 4.

Further, FIG. 1 will be explained to explain the principle of the present invention in detail. FIG. 1 is a circuit diagram showing an example of realizing the above-mentioned current source capable of setting the temperature drift and the current value. In the example shown in the figure, the base of the transistor 30 is biased to a constant potential V _B , and the emitter of the transistor (n−
1) Connect the stage diodes or diode-connected transistors in series. However, n is a natural number. When the potential difference between the potential V _{E at} the connection point of these series-connected diodes (connections) and the resistor 29 and the constant potential V _B can be expressed as nV _BE , the bias current I _{B (T)} is given by Can be represented by

Here, the level shift amount is given by _{IB (T)} × _RL , and only V _BE causes the temperature drift, and other elements R ₁ , R ₂ , R _E , V _CC, etc. Since the influence of temperature drift is considered to be negligible, as a result, the level shift amount is determined by the ratio of the resistance values, and the temperature drift of each resistance value can be neglected.

(1) The level shift amount can be set independently of temperature drift by R ₁ , R ₂ and V _CC .

(2) The temperature drift of the level shift amount can be set independently by n and R _E.

Examples of the present invention will be described below. FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the embodiment shown in FIG. 2, by connecting the base and emitter of the transistor to different constant potential points via a constant current source and a resistor,
The bias current IB _(T) represented by (Equation 5 ₎ is obtained by utilizing the fact that the voltage value of the bias voltage obtained from the base or emitter of this transistor and its temperature drift can be easily set. . Since the above bias voltage can be shared among the transistors forming the plurality of current sources, the circuit scale can be easily reduced. In the case of FIG. 2, sharing the base potential of the transistor 36,
The number of elements can be reduced when other level shift circuits are driven in parallel. (When using the transistor 37 and the like shown by the broken line) Further, the constant current source 35 in FIG. 2 can be replaced with a resistor. However, the terminal of the replaced resistor, which is not connected to the transistor 34, needs to be biased to a constant potential.

Then, in the embodiment shown in FIG. 3, the direction of the temperature drift can also be arbitrarily set as represented by the equation (6).

The embodiment of FIG. 3 is also suitable for parallel driving of level shift circuits, as in FIG.

It goes without saying that in the above-mentioned embodiments, the polarities of the transistors used may be reversed or they may be replaced with FETs.

〔The invention's effect〕

According to the present invention, it is possible to provide a level shift circuit capable of arbitrarily setting the temperature drift of the level shift amount with a simple configuration. Therefore, it is possible to easily expand the operable temperature range of an electronic circuit using the level shift circuit. is there.

[Brief description of drawings]

2 and 3 are circuit diagrams showing an embodiment of the present invention, FIGS. 4 and 5 are circuit diagrams showing a conventional level shift circuit, FIG. 6 is its characteristic diagram, and FIG. And the seventh
The figure illustrates the principle of the present invention. 1 …… Level shift transistor 2 …… Level shift resistor 3 …… Bias current source 4 …… Input terminal 5 …… Output terminal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-119910 (JP, A) JP-A-60-214610 (JP, A) Actual opening 50-24043 (JP, U) Actual opening Sho- 1020 (JP, U) Japanese Patent Sho 54-33828 (JP, B2) Actual Public Sho 53-30205 (JP, Y2)

Claims (3)

[Claims] 1. An emitter of a first transistor whose base is connected to a signal source and which constitutes an emitter follower, is connected to a collector of a second transistor which constitutes a current source circuit via a level shift resistor, and In a level shift circuit for obtaining an output signal from the collector of a second transistor, the emitter of the second transistor is connected to a first via a resistor.
And a constant current source or resistor and the base and emitter of the third transistor are connected in series between the second and third constant potential points, and the connection point is No signal source other than the signal source is connected via the second and first transistors, and a connection point between the constant current source or the resistor and the third transistor is connected. A level shift circuit connected to the base of the second transistor. 2. The emitter of a first transistor whose base is connected to a signal source and which constitutes an emitter follower is connected to the collector of a second transistor which constitutes a current source circuit through a level shift resistor, and In a level shift circuit for obtaining an output signal from the collector of a second transistor, the emitter of the second transistor is connected to a first via a resistor.
Of the constant current source or the resistor and the base and emitter of the third transistor are connected in series between the second and third constant potential points of the constant current source or the resistor. The connection point between the third transistor and the
And a base connected to a second signal source to form an emitter follower.
The emitter of the transistor is connected to the collector of the fifth transistor forming the second current source circuit via the second level shift resistor, and the second output signal is output from the collector of the fifth transistor. At the same time, the emitter of the fifth transistor is connected to the fourth constant potential point via the second resistor, and the connection point of the constant current source or resistor and the third transistor is connected to the fifth constant point. A level shift circuit characterized by being connected to the base of a transistor. 3. The emitter of a first transistor whose base is connected to a signal source and which constitutes an emitter follower is connected to the collector of a second transistor which constitutes a current source circuit through a level shift resistor, and In a level shift circuit for obtaining an output signal from the collector of a second transistor, the emitter of the second transistor is connected to a first via a resistor.
Of the third resistor and the base-emitter of the diode-connected sixth transistor whose collector and base are short-circuited in series between the second and third constant potential points. And a connection point between the resistor and the sixth transistor connected to the base of the second transistor.