JP2003258571A - Circuit for correcting offset of noninverting amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that an offset caused in an output bias voltage is changed in a conventional noninverting amplifier. <P>SOLUTION: A second operational amplifier 14 with the same characteristic as that of a first operational amplifier 11 is connected to the first operational amplifier 11, an input bias voltage is applied to a noninverting input terminal of the first operational amplifier 11 and a noninverting input terminal of the second operational amplifier 14, and an output bias voltage extracted from an output terminal of the second operational amplifier 14 is fed to an inverting input terminal of the first operational amplifier 11 via first and second breeder resistors 13, 15 to make an offset voltage of the output bias voltage extracted from an output terminal of the first operational amplifier 11 constant. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-inverting amplifier offset correction circuit in which an offset voltage of an output bypass voltage taken out from an output terminal is constant.

[0002]

2. Description of the Related Art A non-inverting amplifier using an OP amplifier is used, for example, in a tone control circuit.

FIG. 2 shows a non-inverting amplifier using an OP amplifier. The + input terminal of the OP amplifier 1 receives an input signal and an input bias voltage Vref via a resistor 2.
A resistor 3 is connected between the output terminal and the-input terminal, and the input bias voltage Vref is applied to the-input terminal via the resistor 4.

The input signal Vi applied to the + input terminal
n is amplified by the first OP amplifier 1 and taken out from the output terminal. The output signal taken out switches between resistance 3 and resistance 4,
The size of the non-inverting amplifier can be changed by changing the gain.

Now, the + input terminal voltage of the + input terminal of the OP amplifier 1 is Vp, and the − input terminal voltage of the − input terminal is Vn, Vp.
When −Vn = Vio and the gain is G, the output bias voltage Vout taken out to the output terminal of the OP amplifier 1
Is Vout = G * (Vp-Vn) = G * Vio. In an ideal OP amplifier, the gain G = ∞, so that it can be regarded as Vio = 0. However, since the gain G is actually finite, Vio cannot be zero.

Next, the input bias voltage Vref is calculated. The + input terminal voltage Vp and the − input terminal voltage Vn of the − input terminal are: Vp = Vref Vn = Vp−Vio = Vref−Vio, and Vn = Vref + (Vout−Vref) × R1 / (R
1 + R2). Therefore, Vout−Vref = (Vn−Vref) × (R1 + R2) / R1 = (Vef−Vio−Vref) × (R1 + R2) / R1 = −Vio × (R1 + R2) / R1 Therefore, the output bias voltage Vout is Vout = Vref−Vio. X (R1 + R2) / R1. When the gain G is ideal, Vout = V
Since it is ref, the term of −Vio × (R1 + R2) / R1 is an offset that actually occurs.

That is, the output bias voltage has an offset of (R1 + R2) / R1 times Vio.
When the gain of the non-inverting amplifier is increased, the offset voltage is increased accordingly.

As a result, for example, when the resistor R1 or the resistor R2 is switched to change the gain of the amplifier, switching noise occurs due to the bias fluctuation due to the offset, or
Further, when switching amplifiers having the same configuration but different gains, switching noise may occur due to bias fluctuation caused by offset.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In a non-inverting amplifier that uses an amplifier, an offset voltage related to the resistance value of a resistor that applies a bias is generated in the output bias voltage. Therefore, when the resistance is switched to change the gain of the non-inverting amplifier, noise due to the offset is generated. Similarly, when amplifiers having the same configuration but different gains are switched, noise is generated due to bias fluctuation.

[0010]

According to the present invention, the offset voltage generated in the output bias voltage taken out to the output terminal is made constant, and the present invention is the second OP having the same characteristics as the first OP amplifier for amplifying the input signal. An amplifier is connected, and the input bias voltage is applied to the + input terminal of the first OP amplifier and the second input amplifier.
In addition to the + input terminal of the OP amplifier, an output bias voltage for correction extracted from the output terminal of the second OP amplifier is applied to the − input terminal of the first OP amplifier via a bleeder resistor, and the output terminal of the first OP amplifier (EN) Provided is a non-inverting amplifier offset correction circuit in which an offset voltage of an output bias voltage taken out from is constant regardless of the gain of the non-inverting amplifier.

Further, according to the present invention, a + input terminal to which an input bypass voltage is applied together with an input signal, an output terminal from which an output bias voltage is taken out, and a-input terminal connected to the output terminal via a first resistor are provided. 1st OP amplifier which has and 1st O
A second OP amplifier having the same characteristics as the P amplifier and having a + input terminal to which the input bias voltage is applied, an output terminal for generating an output bias voltage for correction, and a − input terminal connected to the output terminal. The output bias voltage for correction taken out to the second OP amplifier is added to the minus input terminal of the first OP amplifier via the second resistor forming a blider with the first resistor, and taken out from the output terminal of the second OP amplifier. Provided is a non-inverting amplifier offset correction circuit that makes the offset voltage of an output bias voltage constant.

Further, the present invention relates to a non-inverting amplifier offset correction circuit which changes the resistance values of the first resistor and the second resistor to change the gain of the non-inverting amplifier.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-inverting amplifier offset correction circuit of the present invention will be described with reference to FIG.

FIG. 1 is a block diagram of a non-inverting amplifier offset correction circuit according to the present invention. The + input terminal of the first OP amplifier 11 has an input bias voltage Vr via an input resistor 12.
ef is added. The output terminal and the-input terminal of the first OP amplifier 11 are connected by the first bleeder resistor 13. The input bias voltage Vref is added to the + input terminal of the second OP amplifier 14.

The output terminal of the second OP amplifier 14 is connected to the-input terminal and is also connected to the-input terminal of the first OP amplifier 11 via the second bleeder resistor 15.
The first OP amplifier 11 and the second OP amplifier 14 have the same characteristics.

In the non-inverting amplifier, the input signal Vin applied to the + input terminal is amplified by the first OP amplifier 11 and taken out from the output terminal. The magnitude of the extracted output signal can be changed by switching the first bleeder resistor 13 and the second bleeder resistor 15 and changing the gain of the non-inverting amplifier.

Now, assuming that the + input terminal voltage of the first OP amplifier 11 is Vp, the − input terminal voltage is Vn, and Vp-Vn = Vio, the output voltage Vout of the first OP amplifier 11 is Vout = G × (Vp-Vn) = It becomes Vref-Vio. In addition, the + input terminal voltage of the second OP amplifier 14 is set to Vp
2, -input terminal voltage is Vn2, Vp2-Vn2 = Vio
If it is 2, the output bias voltage Vref2 for correction of the second OP amplifier 14 becomes Vref2 = G × (Vp2-Vn2) = G × Vio2. Next, when the bias voltage is calculated, Vp = Vref Vn = Vp-Vio = Vref-Vio. Also, Vn = Vref2 + (Vout−Vref2) × R1 /
R1 + R2 Here, R1 is the resistance value of the second bleeder resistor 15, and R2 is the resistance value of the first bleeder resistor 13.

Therefore, Vout-Vref2 = (Vn-Vref2) * (R1 + R2) / R1 = (Vref-Vio-Vref2) * (R1 + R2) / R1 Vout = Vref2 + (Vref-Vio-Vref2) * (R1 + R2) / R1 Becomes Here, the output bias voltage Vref2 for correction of the second OP amplifier 14 becomes Vp2 = Vref Vn2 = Vp2-Vio2 = Vref-Vio2. Since the second OP amplifier 14 constitutes a buffer, the output bias voltage Vref2 for correction of the second OP amplifier 14 is Vref2 = Vn2 = Vref−Vio2. Therefore, the output voltage Vou of the first OP amplifier 11
t becomes Vout = Vref + (Vref−Vio−Vref2) × (R1 + R2) / R1 = Vref + (Vref−Vio−Vref + Vio2) × (R1 + R2) / R1≈Vref2. The first OP amplifier 11 and the second OP amplifier 14
Has the same characteristics and the output voltage is almost equal to Vref, so that Vio≈Vio2. Therefore, Vref2 = Vref−Vio2≈Vref−Vio.

As described above, since the offset voltage appearing in the output bias voltage of the first OP amplifier 11 is Vio, it is constant regardless of the gain of the non-inverting amplifier. Therefore, for example, the first bleeder resistor 12 and the second bleeder resistor 1
Since there is no bias fluctuation due to the offset voltage when the gain of the non-inverting amplifier is changed by switching between No. 5 and 5, switching noise is prevented. Further, even when amplifiers having the same configuration but different gains are switched, there is no bias fluctuation due to offset, and switching noise can be prevented from occurring.

[0020]

In the non-inverting amplifier offset correction circuit of the present invention, the second OP amplifier having the same characteristics is connected to the first OP amplifier for amplifying the input signal, and the input bias voltage is applied to the + input terminal and the second OP amplifier of the first OP amplifier. In addition to the + input terminal of the amplifier, the output bias voltage for correction taken from the output terminal of the second OP amplifier is applied to the-input terminal of the first OP amplifier via the bleeder resistor. The offset voltage of the output bias voltage extracted from the output terminal of is constant regardless of the gain of the non-inverting amplifier.

[Brief description of drawings]

FIG. 1 is a block diagram of a buffer amplifier device of the present invention.

FIG. 2 is a block diagram of a conventional buffer amplifier device.

[Explanation of symbols]

11 1st OP amplifier 13 1st bleeder resistance 14 Second OP amplifier 15 Second bleeder resistance Vref input bias voltage

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5J066 AA01 AA47 CA13 FA07 HA25                       KA01 MA11 PD01                 5J069 AA01 AA47 CA13 FA07 HA25                       KA01 MA11                 5J500 AA01 AA47 AC13 AF07 AH25                       AK01 AM11 DP01

Claims (3)

[Claims] 1. A second OP amplifier having the same characteristics is connected to a first OP amplifier for amplifying an input signal, and an input bias voltage is applied to a + input terminal of the first OP amplifier and a + input terminal of the second OP amplifier, The corrected output bias voltage extracted from the output terminal of the second OP amplifier is applied to the-input terminal of the first OP amplifier via the bleeder resistance, and the offset voltage of the output bias voltage extracted from the output terminal of the first OP amplifier is not inverted. A non-inverting amplifier offset correction circuit, which is constant regardless of the gain of the amplifier. 2. A positive input terminal to which an input bypass voltage is applied together with an input signal, an output terminal from which an output bias voltage is taken out, and a negative input terminal connected to the output terminal via a first bleeder resistor. A first OP amplifier, a + input terminal having the same characteristics as the first OP amplifier, to which the input bias voltage is applied, an output terminal for generating an output bias voltage for correction, and a-input terminal connected to the output terminal A second OP amplifier having a second OP amplifier having a correction output bias voltage applied to the second OP amplifier via a second bleeder resistor forming a bleeder resistor to the negative input terminal of the first OP amplifier. Two
A non-inverting amplifier offset correction circuit characterized in that an offset voltage of an output bias voltage taken out from an output terminal of an OP amplifier is made constant. 3. The non-inverting amplifier offset correction circuit according to claim 2, wherein the resistance values of the first bleeder resistor and the second bleeder resistor are changed to change the gain of the non-inverting amplifier.