JPH0142530B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a level shift circuit that can arbitrarily set a level shift amount.

A and B in FIG. 1 show conventional level shift circuits. The circuit shown in A has a transistor 4 and a resistor 6 connected between a power supply terminal 2 and a reference potential point, and when an input voltage to be level shifted is applied to an input terminal 8 formed at the base of the transistor 4. , a level shift output is taken out from an output terminal 10 formed on the emitter.

Further, in the circuit shown in B, a constant current source 12, a diode 14, and a constant current source 16 are connected between the power supply terminal 2 and the reference potential point, and the diode 1
A variable resistor 18 is connected to the input terminal 2 formed on the anode side of the diode 14.
When an input voltage to be level-shifted to 0 is applied, a level-shifted output can be taken out from the output terminal 22 formed on the variable resistor 18.

By the way, in the circuit shown in A, transistor 4
The forward voltage drop that occurs between the base and emitter of
It is possible to level shift V _F , and in the circuit shown in B, the level shift amount can be adjusted within the range of the forward drop voltage V _F , and in any circuit, the forward drop voltage V _F It is not possible to set an arbitrary level shift amount exceeding .

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a level shift circuit in which the amount of level shift can be arbitrarily adjusted.

That is, in the level shift circuit of the present invention, a differential pair consisting of first and second transistors 32 and 34 is installed, and the output is taken out from the first transistor and fed back to the base of the second transistor. A third transistor 38 is installed to transfer the current flowing through the third transistor to the first transistor.
A voltage is generated by connecting a differential amplifier 30 with a fourth transistor 40 that draws in through a resistor 50, and a diode 61 with resistors 58 and 60. a level setting circuit 56 that applies the voltage to the base of the transistor and also applies the voltage on the cathode side of the diode to the base of the second transistor via the first resistor; A fifth transistor 64 that takes out an output from the fifth transistor, and a sixth transistor 66 that has a current capacity corresponding to the fifth transistor and draws a current corresponding to the current flowing through the fourth transistor are connected to a second resistor 68. The input signal to be level shifted is applied to one end of the second resistor, and the resistance ratio of the first and second resistors and the current capacity of the fifth and sixth transistors are connected from the other end. The output circuit includes an output circuit (magnification setting circuit 62) that takes out an output signal having a level shift amount determined according to the output signal.

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

FIG. 2 shows an embodiment of the level shift circuit of the present invention.

The differential amplifier 30 includes a first transistor 32
A differential pair consisting of a transistor 36 and a second transistor 34 is installed, and a transistor 36 and a diode 44 as an active load are connected to this differential pair, and a constant current source 48 is also connected. A third transistor 38 is provided to take out the output of the differential pair and feed it back to the base of the transistor 34, and the base of the transistor 38 is connected to the collector of the transistor 32. The collector of the transistor 38 is connected to the base of the transistor 34, and is also connected to the collector of the fourth transistor 40 via a first resistor 50. Further, a transistor 42 whose base is commonly connected to the transistor 38 is installed, the collector of this transistor 42 is connected to the base of the transistor 40, and a diode 46 is connected between the base and emitter of the transistor 40. . Therefore, the differential amplifier 30 constitutes a DC full feedback amplifier.

One input part of the differential amplifier 30, that is, the base of the transistor 32, includes a power supply line to which a drive voltage V _CC is applied from a power supply terminal 52, and a reference potential line in which a grounded reference potential point terminal 54 is formed. A level setting circuit 56 for setting a reference level is installed between the two. This level setting circuit 56 includes resistors 58, 60 and a diode 6.
1, and the reference level is obtained by the forward drop voltage V _F generated in the diode 61. That is, the voltage on the anode side of the diode 61 is applied to the base of the transistor 32, and the voltage on the cathode side of the diode 61 is applied to the base of the transistor 34 via the resistor 50.

A magnification setting circuit 62 is installed on the output side of the differential amplifier 30, which serves as an output circuit for setting a level shift magnification and extracting an output signal having a level shift amount obtained by the magnification. This magnification setting circuit 62 includes a fifth transistor 64,
It is composed of a sixth transistor 66 and a second resistor 68. An input signal to be level-shifted is applied to both ends of the resistor 68, and a terminal 7 is used as an input/output terminal for taking out the level-shifted output signal.
0A and 70B are formed.

In the above configuration, the operation will be explained.

The resistance values of the resistors 50 and 68 are Ra and Rb, the resistance ratio of both is Rb/Ra, the current capacity of the transistors 38 and 42 having a common base is the same, and the transistor 40 and the diode forming a current mirror circuit The current capacity of the transistors 46 and 46 are also set to be the same, and the transistor 64 is set to the same current capacity as the transistors 38 and 4.
By increasing the emitter area of the transistor 66 by N times that of the transistor 40, and by increasing the emitter area of the transistor 66 by N times that of the transistor 40.
4 and 66 have N for transistors 42 and 40.
Double current capacity is set.

Then, when the differential output current flows through the transistors 38 and 42 so that a voltage equal to the forward voltage drop V _F generated in the diode 61 is generated in the resistor 50, the transistors 32 and 34 are in a balanced state.

By the way, the emitter area of the transistors 64 and 66 is set to N times that of the transistors 42 and 40, so if the current flowing through the transistor 42 is _I0 , the area of the emitters of the transistors 64 and 6
6, a current N·I ₀ which is N times the current I ₀ flows. Since this current N・I ₀ flows through the resistor 68, the terminal 70
A level shift amount V _L is set in A and 70B,
This level shift amount V _L is as follows: V _L =V _F ·Rb/Ra·N (1). In this way, the level shift amount V _L is proportional to the product of the resistance ratio Rb/Ra and the current capacity set for the transistors 64 and 66 expressed by the multiplication factor N, and the value is
It is set to an arbitrary value depending on circuit conditions such as the current capacity of the resistors 50 and 68 and the resistance values of the resistors 50 and 68.

Therefore, if an input signal to be level shifted is added from the terminal 70A to one end of the resistor 68, the resistor 68
The output signal level-shifted by the level shift amount V _L set at , is taken out through the terminal 70B on the other end side. Furthermore, even when an input signal to be level-shifted is applied to the terminal 70B, an output signal level-shifted by the level shift amount V _L can be taken out from the terminal 70A.

As explained above, according to the present invention, an arbitrary level shift can be performed according to the resistance ratio of the first and second resistors and the current capacity of the fifth and sixth transistors based on the forward voltage drop of the diode. An input signal to be level shifted can be applied to one end of the second resistor, and an output signal having an arbitrary level shift amount can be taken out from the other end.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional level shift circuit, and FIG. 2 is a circuit diagram showing an embodiment of the level shift circuit of the present invention. 30... Differential amplifier, 32... First transistor, 34... Second transistor, 38... Third transistor, 40... Fourth transistor, 50... First resistor, 56... Level setting circuit, 58, 60...Resistor, 61...Diode,
62... Magnification setting circuit (output circuit), 64... Fifth transistor, 66... Sixth transistor, 68... Second resistor.

Claims (1)

[Claims] 1. A differential pair consisting of a first and a second transistor is installed, and a third transistor is installed that takes out an output from the first transistor and returns to the base of the second transistor. is,
A differential amplifier is installed with a fourth transistor that draws the current flowing through the third transistor through the first resistor, and a resistor is connected to the diode to generate a voltage.
a level setting circuit that applies a voltage on the anode side of the diode to the base of the first transistor and applies a voltage on the cathode side of the diode to the base of the second transistor via the first resistor; a fifth transistor that has a current capacity corresponding to the fifth transistor and draws an output from the first transistor; and a sixth transistor that has a current capacity corresponding to the fifth transistor and draws a current corresponding to the current flowing through the fourth transistor. are connected via a second resistor, an input signal to be level shifted is applied to one end of the second resistor, and the resistance ratio of the first and second resistors and the fifth and fifth resistors are determined from the other end. and an output circuit that takes out an output signal having a level shift amount determined according to the current capacity of the transistor No. 6.