JP2014138202A - Non-inverting amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-inverting amplifier that outputs a DC voltage different from a reference voltage with low noise and low impedance.SOLUTION: The non-inverting amplifier includes a resistive element 2 connected to an output terminal and a negative input terminal, and a resistor 3 connected between the negative input terminal and a ground. The resistive element 2 is an element with a diode characteristic connected to the output terminal and the negative input terminal, and is configured to reduce unwanted noise output when a shifted voltage value of an input DC voltage is output.

Description

  The present invention relates to a forward amplifier, and more particularly, is used in a semiconductor circuit device, and is a positive amplifier that can reduce unnecessary noise that is output when a voltage value of an input DC voltage is shifted and output. The present invention relates to a rotary amplifier (forward amplifier).

  In general, an operational amplifier is a differential amplifier that operates by a potential difference between two inputs, and mainly includes an inverting amplifier and a non-inverting amplifier. The inverting amplifier is an amplifier whose phase of the output signal changes by 180 ° with respect to the input signal, and the non-inverting amplifier is an amplifier whose phase of the input signal and the output signal is the same, and is used in various signal processing circuits. .

  FIG. 1 is a circuit configuration diagram for explaining a conventional non-inverting amplifier. This non-inverting amplifier includes a positive input terminal (+) and a negative input terminal (−), and the positive input terminal is used as a signal input. An operational amplifier that is connected to a terminal and receives an input signal Vref and whose output end is connected to the signal output terminal, one end that is connected to the signal output terminal and the other end that is connected to the negative side input terminal of the operational amplifier, and one end that is a resistance The feedback circuit includes a resistor R1 connected to the other end of R2 and connected to the ground potential point of the power supply potential point. In this non-inverting amplifier, when the resistance values of the resistors R1 and R2 are R1 and R2, which are the same as the signals, respectively, an output signal OUT that is (R1 + R2) / R1 times the input signal is obtained.

That is, in such a conventional non-inverting amplifier (forward amplifier) 100, a resistor having a resistance value R2 connected to the output terminal and the negative input terminal, and a resistor connected between the negative input terminal and the ground. Based on the relative ratio of the resistance value to the resistance of the value R1, the voltage value of the input DC voltage is shifted and output (for example, see Patent Documents 1 to 3).
In FIG. 1 described above, if the input DC voltage value is Vref and the output DC voltage value is Vout, Vout is expressed as Vout = Vref + R2 × I, and Vout is a voltage value different from Vref. Can be generated. However, I = Vref / R1.

  Next, noise that is output unnecessarily in such a state will be described. Assuming that the voltage value of the output noise is Vnout, the input conversion noise generated by the operational amplifier is Vnop, the noise generated from the resistor having the resistance value R1 is Vnr1, and the noise generated from the resistor having the resistance value R2 is Vnr2, Vnout is Vnout. = Vnop × (1 + R2 / R1) + Vnr1 × R2 / R1 + Vnr2. Therefore, when a conventional forward amplifier shifts and outputs the voltage value of the input DC voltage, it amplifies the noise generated from the operational amplifier and the resistor based on the relative ratio of the resistance value, and also eliminates unnecessary noise. Output.

JP 61-203708 A JP-A-5-014071 JP 2010-278489 A

As described above, in the conventional forward amplifier, when the voltage value of the input DC voltage is shifted and output, the noise generated from the operational amplifier and the resistor is amplified based on the relative ratio of the resistance value, There is a problem that unnecessary noise is also output.
The present invention has been made in view of such a problem, and an object of the present invention is to reduce unnecessary noise that is output when a voltage value of an input DC voltage is shifted and output. The object is to provide a normal amplifier capable of this.

  The present invention has been made to achieve such an object, and the invention according to claim 1 includes a resistance element connected to an output terminal and a negative input terminal, a negative input terminal and a ground. A resistor connected in between, and the resistor element is an element having a diode characteristic connected to the output terminal and the negative input terminal, and shifts and outputs the voltage value of the input DC voltage. This is a non-inverting amplifier characterized in that unnecessary noise output at the time can be reduced.

The invention according to claim 2 is the invention according to claim 1, wherein the element having the diode characteristics is a diode.
According to a third aspect of the present invention, in the first aspect of the present invention, the element having the diode characteristics is a MOS transistor, and the gate and drain of the MOS transistor are connected and diode-connected. It is characterized by.

  The invention according to claim 4 is the invention according to claim 1, wherein the element having the diode characteristics is a bipolar transistor, and the base and collector of the bipolar transistor are connected and diode-connected. It is characterized by.

  According to the present invention, a part of noise generated from a noise source can be reduced, and the noise generated from the noise source can be output without being amplified as compared with the prior art. Therefore, it is possible to output a DC voltage with lower noise than conventional.

It is a circuit block diagram for demonstrating the conventional non-inverting amplifier. 1 is a circuit configuration diagram for explaining a first embodiment of a forward amplifier according to the present invention; FIG. It is a figure which shows the electric current between terminals with respect to the voltage between terminals of a diode and resistance. It is a circuit block diagram for demonstrating Example 2 of the normal rotation amplifier which concerns on this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The forward amplifier of the present invention includes a resistance element connected to the output terminal and the negative input terminal, and a resistance connected between the negative input terminal and the ground, and the resistance element is connected to the output terminal and the negative input terminal. This is an element having a diode characteristic connected to the input terminal, and is configured to reduce unnecessary noise that is output when the voltage value of the input DC voltage is shifted and output.

  FIG. 2 is a circuit configuration diagram for explaining a first embodiment of a normal amplifier according to the present invention, in which reference numeral 1 denotes an operational amplifier, 2 denotes a diode (Zd), 3 denotes a resistor (R1), and 200 denotes a normal rotation. Shows the amplifier.

  Hereinafter, the effect of reducing unnecessary noise output in the normal amplifier of the present invention will be described. As shown in FIG. 2, the diode 2 is connected to the output terminal and the negative input terminal of the normal amplifier 200, and the resistor 3 is connected between the negative input terminal and the ground. In FIG. 2, assuming that the input DC voltage value Vref, the output DC voltage value Vout, the threshold value of the diode 2 is Vt, and the impedance of the diode 2 is Zd, Vout is expressed by Vout = Vref + Vt + Zd × I, and Vref and Can generate Vout having different voltage values. However, I = Vref / R1.

  Next, noise that is output unnecessarily in such a state will be described. Assuming that the voltage value of the output noise is Vnout, the input conversion noise generated by the operational amplifier is Vnop, the noise generated from the resistor having the resistance value R1 is Vnr1, and the noise generated from the diode is Vnd, Vnout is Vnout = Vnop × (1 + Zd / R1) + Vnr1 × Zd / R1 + Vnd.

FIG. 3 is a diagram showing the inter-terminal current with respect to the inter-terminal voltage of the diode and the resistor. In the state where the same inter-terminal voltage is applied, the impedance value of the diode is much lower than the resistance value which is the impedance of the resistor FIG.
The diode impedance value Zd will be described with reference to the general diode terminal voltage and current characteristics and the general resistance terminal voltage and current characteristics shown in FIG. As shown in FIG. 3, when a voltage equal to or higher than the threshold voltage Vt of the diode is applied as the voltage between the terminals of the diode, the current between the terminals increases rapidly. In such a state, the impedance value Zd of the diode is expressed as Zd = Vd / Idd by the minute terminal voltage Vd and the minute terminal current Idd. On the other hand, when the minute terminal voltage Vd is applied between the resistance terminals, the minute terminal current Idr flows, and Vd / idd is equal to the resistance value.

Therefore, when comparing the impedance values of the diode and the resistor, the impedance value of the diode is much lower than the resistance value that is the impedance value of the resistor in the state where the same inter-terminal voltage is applied, which is higher than the threshold value of the diode. I understand.
In addition, the main cause of noise generated from the diode is thermal noise, and since this thermal noise is proportional to the square root of the impedance value, the impedance of the diode is very small, so the noise is also very small.
Therefore, in the normal rotation amplifier according to the present invention, Vnout, which is noise that is output unnecessarily, can be approximated to Vnoout≈Vnop, and therefore occurs when the voltage value of the input DC voltage is shifted and output. Unnecessary noise can be reduced more than before.

  FIG. 4 is a circuit configuration diagram for explaining a second embodiment of the forward amplifier according to the present invention, in which reference numeral 12 denotes a transistor. In addition, the same code | symbol is attached | subjected to the component which has the same function as FIG.

  As shown in FIG. 4, the gate and drain of the transistor 12 are connected to the output terminal and the negative input terminal of the normal amplifier 200, the diode-connected transistor 12 is connected, and the negative input terminal and the ground are connected. A resistor 3 was connected between them. In FIG. 4, assuming that the input DC voltage value Vref, the output DC voltage value Vout, the threshold value of the diode-connected transistor 12 is Vt, and the impedance of the transistor 12 is Ztd, Vout is expressed as Vout = Vref + Vt + Ztd × I. Thus, Vout having a voltage value different from the voltage value of Vref can be generated. However, I = Vref / R1.

  Next, noise that is output unnecessarily in such a state will be described. Assuming that the voltage value of the output noise is Vnout, the input conversion noise generated by the operational amplifier is Vnop, the noise generated from the resistor having the resistance R1 is Vnr1, and the noise generated from the diode transistor is Vntd, Vnout is Vnout = Vnop. × (1 + Ztd / R1) + Vnr1 × Ztd / R1 + Vntd

Here, the impedance value of the diode 12 has the same characteristics as the voltage and current characteristics of a general diode shown in FIG. 3 described above, and is equal to or higher than the threshold Vt of the diode-connected transistor 12. When the voltage is applied as the voltage between the terminals of the transistor 12, the current between the terminals increases rapidly.
Therefore, when the diode-connected transistor 12 to which the same inter-terminal voltage is applied is compared with the impedance value of the resistor 3, the same inter-terminal voltage higher than the threshold value of the diode-connected transistor 12 is applied. The impedance value of the diode-connected transistor 12 is much lower than the resistance value that is the impedance value of the resistor.

  The main causes of noise generated from the diode-connected transistor 12 are thermal noise and flicker noise. Since thermal noise is proportional to the square root of the impedance value, since the impedance of the diode-connected transistor 12 is very small, the noise is also very small, but flicker noise remains. Assuming that the thermal noise generated from the diode-connected transistor 12 is Vntds and the flicker noise generated from the diode-connected transistor 12 is Vntdf, Vntd, which is noise generated from the diode-connected transistor 12, is Vntd≈Vntdf. Is done. Further, Vntdf, which is flicker noise, is inversely proportional to the gate area of the diode-connected transistor 12, so that Vntdf can be reduced by increasing the gate area.

Therefore, in the normal amplifier according to the present invention, Vnout, which is noise that is output unnecessarily, can be approximated to Vnout≈Vnop + Vntdf. Unnecessary noise generated during output can be reduced more than before.
That is, as shown in FIG. 4, the diode 12 is connected to the output terminal and the negative input terminal of the normal amplifier 200, and the resistor 3 is connected between the negative input terminal and the ground. The voltage is shifted by a voltage substantially equal to the threshold voltage of the diode 12 with respect to the input voltage. In this state, the amount of noise that is output unnecessarily is improved as compared with the prior art, so that a DC voltage that is lower in noise than the prior art can be output with low impedance.

  In the second embodiment of the forward amplifier according to the present invention, an example of a MOS transistor is shown, but the present invention is not limited to this. For example, a bipolar transistor in which the gate and drain of a transistor are connected and a bipolar base and collector are connected in place of a diode-connected MOS transistor may be used.

  As described above, according to each of the above-described embodiments, it is possible to reduce a part of noise generated from the noise source and output the noise generated from the noise source without being amplified as compared with the related art. Therefore, it is possible to output a DC voltage with lower noise than conventional.

1 Operational amplifier 2 Diode 3 Resistance (R1)
12 transistor 100 non-inverting amplifier (forward amplifier)
200 Forward amplifier

Claims (4)

A resistance element connected to the output terminal and the negative input terminal, and a resistance connected between the negative input terminal and the ground,
The resistance element is an element having a diode characteristic connected to the output terminal and the negative input terminal, and reduces unnecessary noise that is output when the voltage value of the input DC voltage is shifted and output. A forward amplifier characterized in that it can be used.   The forward amplifier according to claim 1, wherein the element having the diode characteristics is a diode.   2. The non-inverting amplifier according to claim 1, wherein the element having the diode characteristics is a MOS transistor, and the gate and drain of the MOS transistor are connected to be diode-connected.   2. The normal amplifier according to claim 1, wherein the element having the diode characteristic is a bipolar transistor, and the base and collector of the bipolar transistor are connected to be diode-connected.

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