JPH0983265A - Level shift circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a detailed level shift by shifting a center voltage of an AC signal from a DC voltage of a 1st DC voltage source to a DC voltage of a 2nd DC voltage source so as to prevent a voltage change of an AC signal based on a temperature change. SOLUTION: An AC signal ΔV deflected around a reference voltage Vref1 of a 1st DC voltage source 8 is applied to an input terminal 10 of the level shift circuit. An output terminal 14 of the level shift circuit connects to collectors of TRs 15, 12 of a current mirror circuit and connects to a 2nd DC voltage source 20 supplying a reference voltage Vref2 via a resistor 19. A voltage across the resistor 19 in this circuit is ΔV, which is constant even if temperature changes without being affected by a base-emitter voltage of the TRs 11, 12, and resistors 17, 18. Furthermore, an AC signal changing around the reference voltage Vref2 of the 2nd DC voltage source 20 able to generate an optional DC voltage is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level shift circuit for level shifting a DC voltage which is the center of an AC signal.

[0002]

2. Description of the Related Art In a state in which an AC signal having a predetermined amplitude is superimposed on a DC voltage of a predetermined level, this AC signal is supplied to a power source V.
When a predetermined signal processing is performed by applying the signal to a signal processing circuit operating at cc, the DC voltage is supplied from a DC voltage source independent of the power supply Vcc even if the power supply Vcc is lowered due to some factor. Therefore, it does not change. Then, the difference between the power supply Vcc and the DC voltage level becomes small,
As a result, in some cases, the sine waveform above the DC voltage level of the AC signal becomes a clipped waveform as the power supply Vcc decreases, and the signal processing circuit may not be able to perform normal signal processing. Therefore, in order to prevent inconvenience such as clipping of the AC signal, a level shift circuit for shifting the DC voltage level downward has been conventionally provided.

A conventional level shift circuit will be described below with reference to FIG. In FIG. 2, (1) is a DC voltage source, which generates a reference voltage Vref. (2) is an AC signal source for generating a sine waveform having an amplitude v.
That is, the AC signal is a signal that changes around the reference voltage Vref with the maximum amplitude v. This AC signal is applied to the base of the transistor (4) via the input terminal (3) of the level shift circuit. The transistor (4) conducts according to the magnitude of the AC signal. The collector of the transistor (4) is connected to a power supply Vcc for driving the level shift circuit, and the emitter of the transistor (4) is connected to the output terminal (6) of the level shift circuit via a plurality of diodes (5) connected in series. Connected. A resistor (7) is connected between the output terminal (6) and ground.
The number of stages of the diode (5) and the resistance value of the resistor (7) are limited to the range in which the transistor (4) can be driven even when the change of the AC signal becomes the minimum value.

Here, the change width of the AC signal is ΔV, the base-emitter voltage of the transistor (4) is VBE, the rising voltage per diode (5) is VF, and the resistance value of the resistor (7) is R, Assuming that n diodes (5) are connected in series, the voltage VO appearing between the output terminal (6) and the ground is represented by Vref + ΔV-VBE-nVF. That is, from the level shift circuit of FIG. 2, an AC signal waveform that changes in a state in which the level is shifted downward by VBE + nVF with respect to the input voltage Vref + ΔV is obtained.

[0005]

However, since the level-shifted output VO appearing at the output terminal (6) is related to the base-emitter voltage VBE of the transistor (4), the output VO is affected by the temperature change. There is an easy problem. Further, since the output VO is also determined by the number of serial stages of the diode (5), the change width of the output VO is in units of VF, and it is impossible to perform more accurate level shift below VF. The shift circuit also has a problem of low versatility.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a level shift circuit capable of ignoring the influence of the temperature change of the base-emitter voltage of a transistor and performing a finer level shift.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is characterized in that an AC signal that changes with a predetermined amplitude centering around a first DC voltage source is provided. Has a first transistor applied to its control terminal,
The first DC voltage source is connected to the second transistor applied to its control terminal and to the input electrodes of the first and second transistors to obtain an output current according to the output current of the first transistor. A current mirror circuit, first and second resistors connected to the output electrodes of the first and second transistors, and a third resistor connected to a connection point between the input electrode of the second transistor and the output of the current mirror circuit. Resistance,
A second DC voltage source that is connected in series with the third resistor and that changes the center voltage of the AC signal; and the center voltage of the AC signal from the DC voltage of the first DC voltage source to the second DC voltage. The point is to shift to the DC voltage of the source.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be specifically described with reference to the drawings. FIG. 1 is a diagram showing a level shift circuit of the present invention. In FIG. 1, (8) is a first DC voltage source, which generates a first reference voltage Vref1. (9) is an AC signal source, which generates an AC signal that changes with the maximum amplitude v. That is, the AC signal corresponds to the first reference voltage Vref1.
It is a signal that changes around. This AC signal is applied to the input terminal (10) of the level shift circuit of the present invention.
(11) is a first transistor, the base is connected to the input terminal, and the AC signal superimposed on the first DC voltage Vref1 is applied via the input terminal (10). Also, (1
2) is a second transistor, and the first DC voltage Vref1 is applied to the base via the input terminal (13). (14) and (15) are current mirror-connected transistors of the same size that form a current mirror circuit.
That is, the transistor (14) is diode-connected, the emitter is connected to the power supply Vcc of the level shift circuit, and the collector is connected to the collector of the first transistor (11). The emitter of the transistor (15) is connected to the power supply Vcc like the transistor (14), and the collector is connected to the collector of the second transistor (12). The output terminal (16) of the level shift circuit is connected to the connection point of the collectors of the second transistor (12) and the transistor (15). (17)
(18) and (19) are first, second and third resistors, each having the same resistance value. First and second resistors (17)
(18) is the first and second transistors (11) (1
It is connected between the emitter of 2) and ground. Also,
One end of the third resistor (19) is connected to the output terminal (19). (20) is a second DC voltage source connected between the third resistor (19) and the ground, and generates the reference voltage Vref2.

In FIG. 1, the signal change of the AC signal source (9) is represented by ΔV, and the first and second transistors (11) and (12).
The base-emitter voltage of VBE1, VBE2 (= VB
E1), the first, second and third resistors (17) (18) (1
Let 9 be the resistance value of R. Then, the transistor (1
4) If the collector currents of (15) are I1, I2, the collector current of the second transistor (12) is I3, and the current flowing through the third resistor (19) is I4, the following relationship holds.

[0010]

[Equation 1]

[0011]

[Equation 2]

Since the collector currents I1 and I2 of the transistors (14) and (15) are in the same relationship,

[0013]

(Equation 3)

[0014] As is clear from the above, the voltage appearing across the third resistor (19) is ΔV, that is, the change itself of the AC signal appears. Therefore, the voltage across the third resistor (19) is not affected by the base-emitter voltage of the first and second transistors (11) and (12), and the first, second and third resistors ( 17)
It is not affected by (18) and (19). In other words, the voltage across the third resistor (19) is not affected by the temperature change and remains constant even if the temperature changes.

Therefore, the second direct current voltage can be generated.
If the DC voltage source (20) is connected between the third resistor (19) and the ground, an AC signal that changes around the second reference voltage Vref2 can be obtained. As is clear from the above description, this AC signal is not affected by the temperature change and is the second DC voltage Vref2 for superimposing the AC signal.
Can be arbitrarily selected, so that this DC voltage level can be set more finely than in the conventional case. Therefore, the level shift circuit of the present invention is highly reliable and versatile. It is obvious that the level shift circuit of the present invention functions normally regardless of whether the second DC voltage Vref2 is higher or lower than the first DC voltage Vref1.

[0016]

According to the present invention, the voltage change of the AC signal due to the temperature change can be prevented, and the DC voltage on the output side on which the AC signal is superimposed can be arbitrarily set. The advantage is that a high circuit can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a level shift circuit of the present invention.

FIG. 2 is a diagram showing a conventional level shift circuit.

[Explanation of symbols]

 (8) First DC voltage source (9) AC signal source (11) First transistor (12) Second transistor (14) (15) Transistor (17) First resistor (18) Second resistor (19) Third Resistance (20) Second DC voltage source

Claims (3)

[Claims] 1. A first transistor to which an AC signal varying around a first DC voltage source with a predetermined amplitude is applied to its control terminal, and a second transistor to which said first DC voltage source is applied to its control terminal. And a current mirror circuit connected to the input electrodes of the first and second transistors to obtain an output current according to the output current of the first transistor, and to the output electrodes of the first and second transistors. A first resistor and a second resistor, a third resistor connected to a connection point between an input electrode of the second transistor and an output of the current mirror circuit, a third resistor connected in series, and a center of the AC signal. A second direct-current voltage source for changing the voltage, and shifting the center voltage of the alternating-current signal from the direct-current voltage of the first direct-current voltage source to the direct-current voltage of the second direct-current voltage source. Le shift circuit. 2. The level shift circuit according to claim 1, wherein the first, second and third resistors have the same value. 3. The level shift circuit according to claim 2, wherein the voltage appearing across the third resistor is a voltage that can ignore the temperature characteristics of the first and second transistors.