JPH11261348A - Voltage amplifier - Google Patents

Abstract

(57) [Problem] To provide a voltage amplifier whose voltage setting resolution by an offset voltage does not depend on a magnification. SOLUTION: An offset resistance correction circuit 23 is provided in parallel with a second resistor 5, and a feedback resistance value of a second operational amplifier 3 is set by a magnification control signal 22, thereby correcting an offset voltage and changing a voltage by variable offset. Keep the setting resolution constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage amplifier capable of changing a magnification and an offset voltage.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional variable-magnification offset voltage amplifier, in which 1 is an input terminal, 2 is a first operational amplifier, 3 is a second operational amplifier, and 4 is a first operational amplifier. A resistor, 5 is a second resistor, 6 is an offset resistance variable circuit,
7 is a first offset variable resistor, 8 is a first offset variable resistor switch, 9 is an nth offset variable resistor, 10 is an nth offset variable resistor switch, 11 is a constant voltage generating circuit, 12 Is a third resistance, 13 is a variable magnification resistance circuit, 14 is a first magnification variable resistance, 15
Is a first magnification variable resistance changeover switch, 16 is an m-th magnification variable resistance switch, 17 is an m-th magnification variable resistance changeover switch, 18 is a third operational amplifier, 19 is a fourth resistance, 20
Is an output terminal, 21 is an offset control signal, and 22 is a magnification control signal. Note that the above operational amplifier is hereinafter referred to as an operational amplifier.

Next, the operation will be described. Input terminal 1
Is amplified by the first operational amplifier 2 and at the same time is offset by the offset voltage Voff output from the second operational amplifier 3. Thereafter, the signal is amplified again by the third operational amplifier 18 and output from the output terminal 20. Here, the offset voltage Voff is generated by the second operational amplifier 3, the offset resistance variable circuit 6, the first resistance 4, the second resistance 5, and the constant voltage generation circuit 11.

More specifically, Voff = (R2 / Rto + 1) Vo (1) R2: resistance value of second resistance 5 Rto: synthesis of resistance value of first resistance 4 and resistance value of offset resistance variable circuit 6 Resistance Vo: output voltage of constant voltage generation circuit 11.

Further, Rto varies depending on whether the first to n-th offset variable resistance changeover switches 8 and 10 are turned on and off, and the resistance value of the n-th offset variable resistance 9 is changed to the first offset variable resistance. Assuming that the resistance value is 2 ^{n -1} times, the following equation is obtained: 1 / Rto = (1 / R1) + ((SWo1 / Ro) +... + (SWon / ( ^2n-1 × Ro))) (2) R1: Resistance value SWo1: first offset variable resistance changeover switch 8 of first resistance 4
ON → 1, OFF → 0 SWon: nth offset variable resistance changeover switch 1
0: ON → 1, OFF → 0 Ro: resistance value of the first offset variable resistor 7 2 ^n-1 × Ro: resistance value of the ^n- th offset variable resistor 9

The first to n-th offset variable resistance changeover switches 8 and 10 are turned on and off by an external n-bit offset control signal 21, and there are 2 ^{n possible} combinations of on and off. When the first to n-th offset variable resistance changeover switches 8 and 10 are all off, that is, when SWo1 to SWon are all 0, 1 / Rto becomes minimum, and conversely, the first to n-th offset variable resistance changeover switches When the switches 8 and 10 are all on, that is, SWo1
When ~ SWon are all 1, 1 / Rto becomes the maximum. When expressed by an equation, 1 / Rto = (1 / R1) to (1 / R1) + (1 / Ro) +... + (1 / (2 ^n-1 × Ro)) = (1 / R1) to (1 ^{/ R1) + ((2 n} -1) / (2 n-1 × Ro)) in the range of (3). Here, Voff is obtained from equations (1) and (3).
Is in the range of: Voff = (R2 / R1 + 1) Vo to (R2 / R1 + R2 × (2 ⁿ -1) / (2 ^n-1 × Ro) +1) Vo (4) Further, the setting resolution ΔVoff of Voff by switching the offset control signal 21 is constant as follows: ΔVoff = (R2 / (2 ⁿ⁻¹ × Ro)) × Vo) (5)

Next, the operation of the third operational amplifier 18 will be considered. The voltage Vain output from the first operational amplifier 2 is applied to the third resistor 12 and the variable-magnification variable circuit 1.
3, amplified by the third operational amplifier 18 and the fourth resistor 19, the output voltage Vout is: Vout = − (R4 / Rta) Vain (6) R4: resistance value of the fourth resistor 19 Rta: third resistor 12 resistance value and magnification resistance variable circuit 1
3 is a combined resistance.

Further, Rta varies depending on whether the first to m-th magnification variable resistance changeover switches 15 and 17 are on or off, and the resistance value of the m-th magnification variable resistance 16 is the first magnification variable resistance. If the resistance value is 2 ^{m -1} times the resistance value of ^No. 14, 1 / Rta = (1 / R3) + ((SWa1 / Ra) +... + (SWam / (2m ^-1 × Ra))) (7) R3: Resistance value of third resistor 12 SWa1: first magnification variable resistance changeover switch 15 is on → 1, off → 0 SWam: mth magnification variable resistance changeover switch 17 is on → 1, off → 0 Ra: first 2 ^{m -1} × Ra: the resistance value of the ^m- th scale variable resistor 16.

The first to mth magnification variable resistance changeover switches 15 and 17 are turned on and off by an external mbit magnification control signal 22, and there are 2 ^m combinations of on and off. When all of the first to m-th magnification variable resistance changeover switches 15 and 17 are off, that is, SWa1
When SWam is 0, 1 / Rta becomes minimum, and conversely, 1st to mth magnification variable resistance changeover switches 15, 17
Are all on, that is, SWo1 to SWon are all 1
In this case, 1 / Rta becomes maximum. When expressed by the formula, 1 / Rta = (1 / R3) to (1 / R3) + (1 / Ra) +... + (1 / (2 ^m-1 × Ra)) = (1 / R3) to (1 ^{/ R3) + ((2 m} -1) / (2 m-1 × Ra)) in the range of (8). From Expressions (6) and (8), Vout is as follows: Vout = − (R4 / R3) Vin 〜 − ((R4 / R3) + (R4 × (2 ^m −1) / (2 ^m−1 × Ra))) Vain (9). Further, the setting resolution ΔVouta of Vout by switching the magnification control signal 22 is fixed as follows: ΔVouta = (R4 / (2 ^m−1 × Ra)) Vain (10)

The voltage value input from the input terminal 1 is Vin
Then, Vain = −A × Vin + (A + 1) Voff (11) A: The magnification of the first operational amplifier 2. Equations (6), (1
From 1), Vout = (R4 / Rta) A · Vin− (R4 / Rta) · (A + 1) Voff (12), and the relational expression between the input voltage Vin and the output voltage Vout is obtained.

Next, the input / output conditions of this circuit will be described.
As shown in FIG. 4, the range V of the voltage value input from the input terminal 1
It is assumed that inH to VinL fluctuate due to factors such as changes in the surrounding environment. On the other hand, the range of the voltage value output to the output terminal 20 VoutH to VoutL must always be kept constant. In the case of such input / output conditions, the resistance values of the offset resistance variable circuit 6 and the magnification resistance variable circuit 13 are set to be different from the external offset control signal 21 and the magnification for the input voltage range VinH to VinL, respectively. Control signal 22
The offset voltage Vo
ff and the resistance value Rta of the magnification resistance variable circuit 13 are changed to output a voltage value range VoutH to the output terminal 20.
~ VoutL can be kept constant.

[0012]

Since the conventional variable magnification offset type voltage amplifier is configured as described above, the setting resolution ΔVout of the output voltage Vout by switching the offset control signal 21, for example, is given by the following equation (12). Since Voff is the resolution in the case of fluctuation, ΔVout = (R4 / Rta) · (A + 1) · Voff (13), where ΔVout is the resolution of the output voltage setting by variable offset. From equation (5), ΔVoff is constant, but from equation (13), the output voltage setting resolution by variable offset is Rta, that is, the variable magnification resistance circuit 1
3 depending on the resistance value. That is, as Rta becomes smaller, the setting resolution becomes worse, and it is difficult to set a desired output voltage value.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has a circuit for canceling a change in the resistance value of the variable magnification resistance circuit 13, and has an output voltage setting resolution by an offset voltage. To obtain a voltage amplifier that does not depend on a variable magnification resistance circuit.

[0014]

A voltage amplifier according to a first aspect of the present invention includes an offset resistance correction circuit provided in parallel with a second resistor, and sets an offset voltage by setting a feedback resistance value of the operational amplifier by a magnification control signal. Correct and maintain constant voltage setting resolution by variable offset.

Further, the voltage amplifier according to the second invention corrects the offset voltage by controlling the voltage input to the positive input of the second operational amplifier by a magnification control signal, and increases the voltage setting resolution by variable offset. Keep constant.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a diagram showing a first embodiment of the present invention, in which 1 to 22 are the same as those in FIG. 23 is an offset resistance correction circuit, 24 is a first offset correction resistance, 25 is a first offset correction resistance changeover switch, 26 is an mth offset correction resistance changeover, and 27 is an mth offset correction resistance changeover switch. .

Next, the operation of the first embodiment will be described in detail. The basic operation is the same as in FIG. Here, an offset resistance correction circuit 23 having the same resistance value and circuit configuration as the magnification resistance variable circuit 13 is provided in parallel with the second resistor 5, and the resistance value of the second resistor 5 Assuming that the resistance value is equal to R3, equation (1) is modified as follows. Voff = (Rta / Rto + 1) Vo (14) Therefore, from the equations (3) and (14), Voff = (Rta / R1 + 1) Vo to (Rta / R1 + Rta · (2 ⁿ −1) / (2 ⁿ⁻¹ ×) Ro) +1) · Vo (15), and the setting resolution ΔVoff of Voff by switching the offset control signal 21 is as follows: ΔVoff = (Rta / (2 ⁿ⁻¹ × Ro)) × Vo (16) This is, when converted into the variation amount ΔVout in the output voltage, from Expressions (13) and (16), ΔVout = (R4 / (2 ⁿ⁻¹ × Ro)) · (A + 1) · Vo (17) It does not depend on the resistance value Rta of the variable resistance circuit 13, and R4, Ro, A, and Vo are fixed values and are constant. Therefore, it is possible to keep the resolution of the voltage setting by the offset variable constant.

Embodiment 2 FIG. FIG. 2 is a view showing a second embodiment of the present invention, in which 1 to 22 are the same as those in FIG. 3, and 23 to 27 are the same as those in FIG. 28
Is a fourth operational amplifier, 29 is a fifth resistor, and 30 is a sixth resistor.

Next, the operation of the second embodiment will be described in detail. The basic operation is the same as in FIG. Here, assuming that the circuit configuration and the resistance value of the offset resistance variable circuit 23 are the same as those of the magnification resistance variable circuit 13 and the resistance value of the sixth resistor 30 is the same as the resistance value R3 of the third resistor 12, offset resistance correction is performed. The combined resistance value of the circuit 23 and the sixth resistor 30 is R
ta. Also, the output voltage V of the fourth operational amplifier 28
o: Vo = −Vos · Rta / R5 (18) Vos: output voltage R5 of the constant voltage generation circuit 11: resistance value of the fifth resistor 29. Therefore, equation (1) is modified as follows. Voff = − (R2 / Rto + 1) · Vos · Rta / R5 (19) Therefore, according to equations (3) and (19), Voff = − [(R2 / R1 + 1) to (R2 / R1 + R2 · (2 ⁿ −1)) / (2 ^n-1 × Ro) +1)] Vos · Rta / R5 (20), and the setting resolution ΔVoff of Voff by switching the offset control signal 21 is ΔVoff = (R2 / (2 ⁿ⁻¹ × Ro)) × Vos · Rta / R5 (21) This is converted into a variation ΔVout in the output voltage, and from Expressions (13) and (21), ΔVout = (R4 / R5) · (A + 1) · R2 / (2 ⁿ⁻¹ × Ro) (22) , R4, R5, Ro, R2, and A are constant, independent of the resistance value Rta of the variable magnification resistance circuit 13. Therefore, it is possible to keep the resolution of the voltage setting by the offset variable constant.

[0020]

According to the first aspect, the offset resistance correction circuit is provided in parallel with the second resistor so that the feedback resistance value of the operational amplifier can be set by the magnification control signal. Also, the offset voltage can be corrected, and the voltage setting resolution by the variable offset can be kept constant.

According to the second aspect of the present invention, the voltage input to the positive input of the second operational amplifier can be controlled by the magnification control signal, so that the offset voltage is corrected even when the magnification changes in the subsequent stage. Thus, there is an effect that the voltage setting resolution by the variable offset can be kept constant.

[Brief description of the drawings]

FIG. 1 is a diagram showing Embodiment 1 of a voltage amplifier according to the present invention.

FIG. 2 is a diagram showing Embodiment 2 of a voltage amplifier according to the present invention.

FIG. 3 is a diagram illustrating a conventional voltage amplifier.

FIG. 4 is a diagram showing input / output voltage conditions.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Input terminal, 2 1st operational amplifier, 3 2nd operational amplifier, 4 1st resistance, 5 2nd resistance, 6 offset resistance variable circuit, 7 1st offset variable resistance,
8 first offset variable resistance changeover switch, 9 nth offset variable resistance changer, 10 nth offset variable resistance changeover switch, 11 constant voltage generation circuit, 12
3rd resistor, 13 magnification variable resistance circuit, 14 first magnification variable resistance, 15 first magnification variable resistance changeover switch, 16 mth magnification variable resistance, 17 mth magnification variable resistance changeover switch, 18 3rd operational amplifier, 19
4th resistor, 20 output terminals, 21 offset control signal, 22 magnification control signal, 23 offset resistance correction circuit, 24 first offset correction resistor, 25 first offset correction resistance changeover switch, 26 m offset correction Resistance, 27 m-th offset correction resistance changeover switch, 28 4th operational amplifier, 29 5th resistance, 30 6th resistance.

Claims (2)

[Claims] 1. An input terminal, a first operational amplifier (op-amp) to which the input terminal is connected to the negative input terminal, and a first operational amplifier to which a positive input terminal and an output terminal of the first operational amplifier are connected. 2 operational amplifier, a first resistor having one end connected to the negative input terminal of the second operational amplifier and the other end grounded, and a first to a first connected to one end of the first resistor. n
An offset variable resistor (n is an integer of 2 or more), one end of which is connected to the other end of each of the first to n-th offset variable resistors, and the other end is connected to the other end of the second resistor; And an offset resistance variable circuit constituted by first to n-th offset variable resistance changeover switches that are opened and closed by an offset control signal from the first and second operational amplifiers. A second resistor connected to the negative input terminal of the operational amplifier, and first to m-th (m is an integer of 2 or more) connected to one end of the second resistor
, One end of which is connected to the other end of each of the first to m-th offset correction resistors, the other end of which is connected to the other end of the second resistor, and which is opened and closed by an external magnification control signal. An offset resistance correction circuit configured by first to m-th offset correction resistance changeover switches;
A constant voltage generating circuit connected to a positive input terminal of the second operational amplifier; a third resistor having one end connected to an output terminal of the first operational amplifier; and another end of the third resistor A third operational amplifier having a negative input terminal connected thereto and a positive input terminal grounded, and a first operational amplifier connected to one end of the third resistor.
To an m-th variable resistor, one end of which is connected to the other end of the first to m-th variable resistor, and the other end is connected to the other end of the third resistor, and is opened / closed by the magnification control signal. A variable resistance variable circuit constituted by first to m-th variable magnification resistance changeover switches, one end of which is connected to a negative input terminal of the third operational amplifier and the other end is an output terminal of the third operational amplifier. And a fourth resistor connected to the third operational amplifier, and an output terminal connected to the output terminal of the third operational amplifier. 2. An input terminal, a first operational amplifier having the input terminal connected to the negative input terminal, and a second operational amplifier having a positive input terminal connected to the output terminal of the first operational amplifier. An amplifier, a first resistor having one end connected to the negative input terminal of the second operational amplifier and the other end grounded, and first to n-th (n) connected to one end of the first resistor. Is an integer of 2 or more). One end is connected to the other end of each of the first to n-th offset variable resistors, and the other end is connected to the other end of the second resistor. An offset resistance variable circuit constituted by first to n-th offset variable resistance changeover switches that are opened and closed by an offset control signal; and one end connected to the output terminal of the second operational amplifier and the other end connected to the second operational amplifier The second resistor connected to the negative input terminal of A third resistor having one end connected to the output terminal of the first operational amplifier; and a third resistor having a negative input terminal connected to the other end of the third resistor and a positive input terminal grounded. And a first to m-th (m is an integer of 2 or more) magnification varying resistors connected to one end of the third resistor, and the other end of each of the first to m-th magnification varying resistors. A magnification resistance variable circuit having one end connected and the other end connected to the other end of the third resistance, and configured by first to m-th magnification variable resistance changeover switches that are opened and closed by the magnification control signal; A fourth resistor having one end connected to the negative input terminal of the third operational amplifier and the other end connected to the output terminal of the third operational amplifier, and an output connected to the output terminal of the third operational amplifier. And an output terminal connected to the positive input terminal of the second operational amplifier and a positive input terminal. A fourth operational amplifier having a grounded terminal, a fifth resistor having one end connected to the negative input terminal of the fourth operational amplifier, and a constant voltage generator connected to the other end of the fifth resistor. A circuit, a sixth resistor having one end connected to the negative input terminal of the fourth operational amplifier, and the other end connected to the output terminal of the fourth operational amplifier;
A first to an m-th offset correction resistor connected to one end of the sixth resistor, one end connected to the other end of the first to m-th offset correction resistor, and the other end connected to the second resistor; A voltage amplifier comprising: an offset resistance correction circuit connected to the other end and configured by first to m-th offset correction resistance changeover switches that are opened and closed by an external magnification control signal.