JPS59181802A - Current input type amplifier - Google Patents

Abstract

PURPOSE:To attain low voltage operation by setting a DC potential of an output to a half of a power supply potential and holding always a DC potential setting value of an output side to ensure a broad dynamic range of a current input type amplifier. CONSTITUTION:A constant current source I0 is connected between a power supply Vcc and a terminal of a transistor Q corresponding to an inverting input terminal (-). Then, the relation of current sources I1 and I2 is taken as I1=I2+ I0. In setting the ratio of resistors R3/R1 to 1/2, the output Vout is obtained as Vout=Vcc/2+VBE/2-I0R3. In setting VBE/2=I0R3, the output Vout is kept always to Vcc/2 and a wide dynamic range is ensured even at a low power supply voltage Vcc where a voltage VBE is not neglected or even if the power supply Vcc is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a current input type amplifier, and more particularly to an improvement in its output potential determining section.

[Technical background of the invention and its problems]

2. Description of the Related Art Conventionally, a current input type amplifier device configured as shown in FIG. 1 is known as a current input type amplifier device widely used in general electronic devices including audio devices.

That is, the power supply Vcc is connected to the non-inverting input terminal (+) of the current input type amplifier 11 via the resistor R1, and the feedback resistor R3 is connected to the inverting input terminal (-) from the output terminal Vout.
In addition, the capacitor C and the resistor R2 are connected in series from the input signal source VIN.

Since it is a current input type, it operates so that the currents I1 and I2 flowing into the non-inverting input terminal (+) and the inverting input terminal (-) are equal.

In this case, if the resistors R1 and R3 are selected so that R1=2R3, the DC output potential from the output terminal Vout is
Vout(DC)=1/2Vcc. However, this is the case when the DC potentials of the non-inverting input terminal (+) and the inverting input terminal (-) are both zero potential, and selecting the DC output potential to 1/2 Vcc in this way is normally a dynamic This is to make the range as wide as possible.

FIG. 2 shows a specific example of FIG. 1, and parts configured similarly to those in FIG. 1 are given the same reference numerals.

That is, Q1 and Q2 in FIG. 2 are transistors forming a current mirror, and the collector of the diode-connected transistor Q1 is connected to correspond to the above-mentioned inverting input terminal (-). Further, the collector of the transistor Q2 corresponds to and is connected to the non-inverting input terminal (+). The collector of the transistor Q3, whose base is coupled to the collector of the transistor Q2, is connected to a constant current load I3, and is also connected to the base of the transistor Q4. The collector of this transistor Q4 is the output terminal V
It is connected to the constant current load I4 as well as to the constant current load I4.

Therefore, the following relationship holds true in the above configuration.

However, VBE is the pace emitter voltage of the transistor.

I1R1+VBE(Q3)=Vcc...(1)I2R3
+VBE (Q1) = Vout (DC)... (2) Here, I1 = I2 (however, the influence of pace current is ignored), VBE (Q1) = VBE (Q3), R1 = 2R
3, from (1) and (2) Vout(DC)=1
/2Vcc+1/2VBE...(3) can be obtained.

This equation (3) is normally expressed as VBE≪Vcc, so Vout(D
C)≒1/2Vcc...(4).

However, when the power supply Vcc potential decreases to a value where VBE cannot be ignored, Vout (DC) becomes 1
/2Vcc.

In other words, by appropriately changing the ratio of resistors R1 and R3, Vout (DC) = 1 only for a certain Vcc.
/2Vcc, but if Vcc changes, it becomes impossible to secure it.

This has disadvantages in that the dynamic range characteristics are narrowed and inhibited, and the device is not suitable for low voltage operation.

[Purpose of the invention]

Therefore, the present invention has been made in view of the above points, and provides an extremely good current input type amplifier device that has been improved to ensure the widest possible dynamic range characteristics and to enable low voltage operation. It is intended to.

[Summary of the invention]

That is, the current input type amplifier device according to the present invention has a non-inverting input terminal to which a first predetermined current is supplied from a power supply and an inverting input terminal to which a second predetermined current is fed back from the output side, and a current input type amplifier configured by approximately calculating the first and second predetermined currents as well as the current input type amplifier; and a DC potential setting value of the output side is always maintained with respect to the inverting input terminal of the current input type amplifier. and a constant current source that supplies a third predetermined current.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, as shown in FIG. 3, one end of the input signal source VIN is connected to ground (GND), and the other end is connected to a diode-connected transistor corresponding to the inverting input end (-) via a capacitor C and a resistor R2 in series. Connected to the collector of Q1.

Here, the transistor Q1 and the transistor Q2 form a current mirror by having their bases directly connected, and their emitters are both grounded (GN
D).

The collector of transistor Q2 is connected to the non-inverting input terminal (
+), and is connected to the power supply Vcc via a resistor R1 serving as a load, and is also connected to the base of the transistor Q3. This transistor Q3 has its collector connected to the power supply Vcc via a constant current load I3, and also connected to the base of the transistor Q4, and further has its emitter connected to ground (GND). The transistor Q4 has its emitter connected to the power supply Vcc, and its collector connected to the output terminal Vout and to ground (GND) via a constant current load I4.

The output terminal Vout is connected to the collector of the transistor Q1 corresponding to the inverting input terminal (-) via a feedback resistor R3.

The above configuration is similar to that of the conventional current input type amplifier device shown in FIG. 2, but in FIG. A constant current source I0 is connected between them.

In the configuration shown in FIG. 3 as described above, the following relationship holds true in equations (1) and (2) described above.

I1=I2+I0...(5) However, even in equation (5), the influence of the base current is ignored.

Here, as VBE (Q1) - VBE (Q3) (1)
, (2) and (5) to find Vout(DC). Using this equation (6), we get:

By the way, in order to ensure as wide a dynamic range as possible and make it suitable for low voltage operation such as during reduced voltage, the second and third terms on the right side of equation (7) must be set so that they cancel each other out. In the end, all that is required is to inject the current from the constant current source I0.

In other words, even if Vcc is so low that VBE cannot be ignored, or even if Vcc is changed,
Out (DC) can always be kept at 1/2 Vcc.

FIG. 4 shows another embodiment, in which the collector of the transistor Q2 in the embodiment of section 3 is connected to the power supply Vcc through the constant current load I1 instead of the resistor R1, and the collector of the transistor Q1 is connected to the power supply Vcc through the constant current load I1 instead of the resistor R1. , a diode-connected transistor Q1' that loads the resistor R1, and a transistor Q2' whose bases are directly connected to each other.
The third exception is to combine the current mirrors that are
The configuration is similar to that shown in the figure.

Therefore, in the configuration shown in FIG. 4, R1=2R3
If there is no constant current source I0 when selected, Vout (DC) = 1/2Vcc + 1/2VBE + I1
If I0=I1, Vout(DC)=1/2Vcc+1/2VBE, but if I0=I1+VBE/2R3, Vout=1/2VCC.

It goes without saying that the present invention is not limited to the embodiments described above and illustrated, and that various modifications and applications can be made without departing from the gist of the invention.

〔Effect of the invention〕

Therefore, as detailed above, according to the present invention, it is possible to provide an extremely good current input type amplifier device that has been improved to ensure as wide a dynamic range as possible and to enable low voltage operation. becomes.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the basic configuration of a current input type amplifier, FIG. 2 is a circuit diagram of a conventional amplifier embodying FIG. 1, and FIG. 3 is a current input type amplifier according to the present invention. FIG. 4 is a circuit diagram showing one embodiment of the apparatus, and FIG. 4 is a circuit diagram showing another embodiment. VIN...Input signal source, C...Capacitor, R1-R3...Resistor, Q1-Q4...Transistor, I3, I4...Constant current load, Vout...Output terminal, Vcc...Power supply, (GND)...
Ground, (+)...Non-inverting input terminal, (-)...Inverting input terminal, I
0... Constant current source. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Claims] It has a non-inverting input terminal to which a first predetermined current is supplied from the power supply and an inverting input terminal to which a second predetermined current is fed back from the output side, and the DC potential on the output side is set to approximately 1/1/2 of the power supply potential.
2 and the first and second predetermined currents are set to be substantially equal; and a constant current source that supplies a third predetermined current sufficient to enable the current input type amplifier.