JPH0438568Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field of the Invention] The present invention relates to an inverting differential amplifier circuit with high input impedance suitable for low voltage power supplies (approximately 1V).

[Problem that the invention attempts to solve]

Generally, non-inverting differential amplifier circuits are used, but low-voltage power supplies cannot be used because the input dynamic range is small. To solve this problem, an inverting differential amplifier circuit is used.

FIG. 3 shows a general inverting differential amplifier circuit. 1 is a differential amplifier circuit, a reference voltage source 2 is connected to its non-inverting terminal, resistors R ₁ and R ₂ are connected to its inverting input terminal, and the other end of resistor R ₁ is connected to input terminal 4. and the other end of resistor _R2 is output terminal 6.
connected to. 3 is a bias voltage source, and 6 is an output terminal.

In FIG. 3, if the signal current flowing from the input terminal 4 to the non-inverting terminal is _I1 , the following equation holds true.

I ₁ =V _IN −V _REF /R ₁ (1) (V _IN : input voltage, V _REF : voltage of reference voltage source 2) Further, the output voltage V _OUT is expressed as follows.

V _OUT =V _REF −R ₂ /R ₁ (V _IN −V _REF ) = −R ₂ /R ₁ V _IN + (1 + R ₂ /R ₁ )V _REF ...(2) Such an inverting differential amplifier circuit Then, as shown in equation (1), a current I ₁ is required to flow into the resistor R ₁ , and when viewed from the input terminal 4, the resistor R ₁ becomes a load, and in a circuit where the impedance of the circuit connected to the input side is large, I can not use it. In other words, as is clear from equation (2), when the resistance R ₁ corresponding to the impedance of the circuit connected to the input side becomes extremely large, the output voltage V _OUT becomes small, which causes the gain of the inverting amplifier circuit to become small. becomes.

[Purpose of invention]

An object of the present invention is to provide an inverting differential amplifier circuit having high input impedance characteristics.

An object of the present invention is to provide an inverting differential amplifier circuit having high input impedance characteristics suitable for low voltage sources.

[Example of idea]

An inverting differential amplifier circuit according to the present invention will be explained based on FIGS. 1 and 2.

FIG. 1 shows an embodiment of the inverting differential amplifier circuit of the present invention. In addition to the inverting differential amplifier circuit of FIG. 3, a circuit system 9 is supplied with a single-ended output to the input terminal side. It is equipped with

FIG. 2 is a circuit diagram showing a more specific circuit of FIG. 1. In the figure, a differential amplifier circuit 1 consists of a differential pair of transistors Q ₁ and Q ₂ and a constant current source circuit 5, and output currents having inverted phases are derived from the active load circuit. The active load circuit consists of diode D ₁ and transistors Q ₃ , Q ₄ and diodes.
A current mirror circuit is constructed from D ₂ and transistors Q ₅ and Q ₆ , respectively. The collector of transistor Q ₃ is the anode of diode D ₃ and the transistor Q ₇
The collector of _Q7 is connected to the collector of transistor _Q5 , making it a single-ended output. Further, the collector of the transistor Q ₄ is connected to the collector of the transistor Q ₈ , and the base of the transistor Q ₈ is connected to the anode of the diode D ₄ and the collector of the transistor Q ₆ , so that a single-ended output is similarly provided. Diode D ₃ and transistor Q ₇ and diode D ₄ and transistor Q ₈ each constitute a current mirror circuit. A resistor R ₁ is connected between the base of the transistor Q ₁ and the input terminal 4, and a feedback resistor R ₂ is connected between the base of the transistor Q ₁ and the commonly connected collectors of the transistors Q ₅ and Q ₇ . Further, the commonly connected collectors of transistors Q ₄ and Q ₈ are connected to input terminal 4 . A reference voltage source 2 is connected to the base of the transistor Q ₂ , and a bias voltage source 3 is connected to the input terminal 4 . transistor
The commonly connected collectors of Q ₅ and Q ₇ are output terminal 6.
It is connected to the.

When the input voltage V _IN superimposed on the bias voltage source 3 is supplied to the input terminal 4, a mirror current (I ₀ + I ₁ ) flows from the transistors Q ₃ and Q ₄ in the output stage of the active load circuit, and the other _The mirror current ( _{I 0}
−I ₁ ) flows out. A mirror current (I ₀ −I ₁ ) flows from the collector of transistor Q ₆ into diode D ₄ . A collector current (I ₀ +I ₁ ) flows into the collector of the transistor Q ₈ forming a mirror pair with the diode D ₄ . Also, from the collector of transistor _Q4 ,
Mirror current (I ₀ + I ₁ ) flows into it. As the surplus current, a current of 2I ₁ flows into the resistor R ₁ , and a current of 2I ₁ flows into the resistor R ₂ . On the other hand, as shown in Fig. 3, the input current I ₁ flowing from input terminal 4 is resistor R ₂
flows into. Therefore, in the embodiment shown in FIG. 2 as in FIG. 1, the current of 2I ₁ flowing through the resistor R ₁ flows into the resistor R ₂ , so the input/output current from the input terminal 4 can be reduced to approximately zero. . That is, the input impedance seen from the input terminal can be made high impedance. On the other hand, a mirror current (I ₀ − I ₁ ) flows out from the collector of transistor Q ₅ , and resistor R ₂
Since a current of 2I ₁ flows into the collector of the transistor Q ₇ and a mirror current of (I ₀ +I ₁ ) flows into the collector of the transistor Q 7 , it does not flow into the output terminal 6.

Further, an output may be obtained by adding a transistor to the output stage of another current mirror circuit in the active load circuit 8.

In such an inverting amplifier circuit, the voltage drop between the power supply voltage Vcc and ground is such that the forward voltage of diode _D1 is approximately
0.7V, the saturation voltage of transistor _Q1 is approximately 0.2V, and the voltage drop of constant current source circuit 5 is approximately 0.1V.
Since the total sum is approximately 0.9, it can be operated satisfactorily even when the power supply voltage is 1V.

Of course, it is obvious that the structure can be constructed using elements of conductivity types opposite to those of the embodiments.

[Effect of idea]

The inverting differential amplifier circuit of this invention has a power supply voltage of
It operates even at a voltage of 1V or less, and has an effective input characteristic with high input impedance.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining one embodiment of an inverting differential amplifier circuit according to the present invention, and FIG. 2 is a circuit diagram showing one embodiment thereof. FIG. 3 is a circuit diagram showing an example of a general inverting differential amplifier circuit. 1...Differential amplifier circuit, 2...Reference voltage source, 3...
... Bias voltage source, 4 ... Input terminal, 5 ... Constant current source circuit, 6 ... Output terminal, 7, 8 ... Active load circuit consisting of current mirror circuit.

Claims (1)

[Scope of utility model registration request] A differential amplifier circuit comprising first and second transistors forming a differential pair and a constant current source circuit, in which a reference voltage source is supplied to one input terminal and an input signal is supplied to the other input terminal; A first active load circuit including third and fourth transistors in the output stage and a second active load circuit including fifth and sixth transistors in the output stage for deriving outputs with mutually inverted phases from the circuit. The collector of the third transistor is connected to the anode of the first diode, the connection point thereof is connected to the base of the seventh transistor, and the collector of the seventh transistor is connected to the anode of the first diode. The collector of the fourth transistor is connected to the collector of the eighth transistor, and the base of the fourth transistor is connected to the anode of the fourth diode. is connected to the collector of the transistor, first and second resistors are connected to the base of the first transistor, the other end of the first resistor is connected to the input terminal, and the fourth and eighth resistors are connected to the base of the first transistor. connected to the collector of the transistor, and the second
An inverting differential amplifier circuit characterized in that the other ends of the resistors are connected to the collectors of the fifth and seventh transistors and also to the output terminals.