JPH10313221A - Voltage generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise generated at the switching time in a voltage generator capable of switching a generated output voltage range. SOLUTION: A voltage hold circuit 10 consisting of an operational amplifier 3, a voltage holding capacitor C1, and a phase compensation resistor R5 prevents production of an excess voltage or a very small voltage in the case of selecting a voltage generating range. Furthermore, a negative feedback circuit 12 that is driven when the voltage generating range is selected is provided between an input and an output of a pre-stage amplifier of the voltage hold circuit 10, and an output voltage of the prestage amplifier is set to 0V to prevent production of a spike noise P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage generator whose voltage generation range (range) can be switched by a switch.
More particularly, the present invention relates to a voltage generator that reduces unnecessary voltage generated when switching ranges.

[0002]

2. Description of the Related Art FIGS. 7 and 8 are block diagrams showing the configuration of a conventional voltage generator. FIG. 7 is a basic configuration block diagram of a voltage generator capable of switching a voltage generation range by a switch, and FIG. 8 is a configuration block diagram in which the configuration of FIG. 7 is improved. The same parts are denoted by the same reference numerals. First, FIG. 7 will be described. In FIG. 1, reference numeral 1 denotes a reference voltage generator constituted by a Zener diode or a digital-to-analog converter using the Zener diode, and generates a specific reference voltage E. Reference numeral 2 denotes an operational amplifier, and reference numerals 6 and 7 denote switches (hereinafter referred to as [S]), which are FET semiconductor switches or reed switches. R1 and R2 are input resistances of the operational amplifier 2, and the reference voltage E is connected to the negative-phase input terminal of the operational amplifier 2 via S6 and a resistor (hereinafter referred to as [R]) R1 or S7 and R2. . The output voltage V of the output terminal 11 is connected to the negative-phase input terminal of the operational amplifier 2.
The feedback resistor R3 from O is also connected, the positive-phase input terminal is grounded, and an inverting amplifier is configured as the entire system.

In the configuration shown in FIG. 7, one of S6 and S7 is on (connected) and the other is off (cut off). The output voltage Vo of the output terminal 11 changes as in the following equation by switching between S6 and S7, and the output range is switched. When S6 is on and S7 is off; Vo = −R3 · E /
R1 When S7 is on and S6 is off; Vo = −R3 · E /
R2 For example, E = −0.01 V, R1 = 10 kΩ, R2 = 1
Assuming that kΩ and R3 = 10 kΩ, when S6 is on, V
o = 0.01 V, and when S7 is on, Vo = 0.1
Therefore, the output voltage Vo can be switched to a range of 10 times.

As described above, when the output voltage Vo is switched from 0.01 V to 0.1 V, it is impossible to switch S6 and S7 completely and instantaneously, so that the following sequence is generally used. There are two possibilities. Both S6 and S7 are turned on from the state where S6 is on, and then S
6 is turned off, and S6 is turned on, S6 and S7 are both turned off, and then S7 is turned on.

In the above case, when S6 and S7 are both on, the input resistance is a parallel connection of R1 and R2, so Vo in the above example is Vo =-(R1 + R2) .R3.E / R1 · R2 = 0.
A voltage of 11V is generated. That is, when trying to switch from 0.01 V to 0.1, once from 0.01 V to 0.11 V
Then, since the voltage becomes 0.1 V, an excessive voltage may be generated at one time, which may cause a trouble such as damage to a load device or the like. In the above case, S6 and S7
When both are off, the output voltage Vo becomes 0.00V. Therefore, when switching from 0.01V to 0.1V, the output voltage Vo once becomes 0.00V from 0.01V, and then becomes 0.1V.
Since the voltage becomes 1 V and an excessively small voltage is generated at one time, a test of a material having hysteresis may be hindered.

In order to solve such a problem, a configuration shown in FIG. 8 has been considered. The configuration of FIG.
Reference voltage E is applied to S6 and R1 or S7
, And R2 together with the feedback resistor R3, and the negative-phase input terminal is grounded. The output voltage V1 of the operational amplifier 2 is connected to the opposite-phase input terminal of the operational amplifier 3 via R4 and the switch S8 together with a phase compensation resistor R5.

The other end of the phase compensation resistor R 5 is connected to one end of a voltage holding (holding) capacitor C 1, and the other end of the voltage holding capacitor C 1 is connected to the output terminal of the operational amplifier 3. The positive input terminal of the operational amplifier 3 is grounded, and a voltage hold circuit 10 is formed by the operational amplifier 3, the voltage holding capacitor C1, and the phase compensation resistor R5. The value of C1 is several hundred pF to several μF, and the value of R5 is around 100Ω. The other end of the feedback resistor R3 is connected to the output terminal of the operational amplifier 3, and the system system has an inverting amplifier configuration.

In the circuit of FIG. 8, the switch 8 is normally on, but when S6 and S7 are switched, S8 is turned off and the output voltage Vo is held in the voltage holding capacitor C1, and the switching operation is completed. The switch 8 is turned on later. That is, as shown in FIG. 9, S8 is turned off for a predetermined time t _H before and after the switching of S6 and S7, the output voltage Vo is held in the capacitor C1, and Vo is output as it is, and the basic circuit of FIG. Is solved, and as a result, the output voltage Vo is switched from 0.01 V to 0.1 V as shown in FIG. 9D.

[0009]

By using the voltage generator having the circuit configuration shown in FIG. 8, the generation of an excessive voltage or an undervoltage when switching between S6 and S7 according to the circuit configuration of FIG. 7 can be eliminated. However, a problem may also occur in the conventional voltage generator shown in FIG.
It holds the output voltage Vo by the capacitor C1 during t _{H in} FIG. 9E, but during this time, the system of the system is open because S8 is off. Therefore, the output voltage V1 of the operational amplifier 2, which is the operational amplifier of the voltage hold circuit 10, is saturated. This saturation voltage is about ± 13 V when the drive voltage of the operational amplifier 2 is ± 15 V, for example. Then, the switching period t _H ends,
The output voltage Vo of the system at the moment when S8 is turned on is Vo = −R
A voltage of 5 · V1 / R4 is generated, which generates a spike-like noise P like P shown in FIG. 10E.

The magnitude of the spike noise P is determined by the resistance R
For example, if R4 is 1 kΩ, R5 is 100Ω, and V1 is 10 V, a spike-like noise of about 1 V is generated in Vo, which is related to 4 and R5 and the magnitude of the saturation voltage V1 of the operational amplifier 2. This value does not cause much problem when the output voltage Vo to be switched is 1 V or more. However, when the output voltage Vo is switched to 0.1 V as in the above-described example, the noise becomes 10 times the voltage of 1 V, and the device, etc. Breakage or various problems may occur. An object of the present invention is to reduce spike noise P at the time of this switching.

[0011]

In order to achieve the above object, the present invention provides a method for holding the output voltage of the operational amplifier of the voltage holding circuit while holding the output voltage of the system during t _H when S8 is turned off. The saturation of the voltage V1 is prevented and the output voltage V
A negative feedback circuit is provided between the input and output of the operational amplifier so that 1 becomes zero. To this end, a negative feedback circuit is connected via a switch S, and the switch S is turned on or off for t _H to form a negative feedback circuit, the output voltage V1 of the operational amplifier is held at zero, and the voltage hold is released. The generation of a later spike voltage is suppressed. Various circuit configurations have been devised in the configuration of this system.

This specification describes several circuit configurations,
For simplicity, all explanations will be made with an inverting amplifier system. However, a non-inverting amplifier system can be easily applied in the prior art, and the present invention extends not only to the embodiment but also to a voltage generator using the inverting amplifier system and the non-inverting amplifier system according to the prior art.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings. FIG. 1 is a block diagram of a basic embodiment of the present invention, FIG. 2 is a timing chart of the circuit of FIG. 1, and FIGS. 3, 4, 5 and 6 show other embodiments. 7 and 8 are denoted by the same reference numerals. First, the configuration diagram of FIG. 1 will be described with reference to the timing chart of FIG.

A negative feedback circuit 12 is connected between the input and output terminals of the operational amplifier 2 of the voltage hold circuit 10 of FIG. The negative feedback circuit 12 is configured by an inverting amplifier, and the amplification degree may be several times to about 100 times. For example,
If R6 is 1 kΩ and R7 is 50 kΩ, the amplification is 5
It becomes 0 times. The input of the negative feedback circuit 12 is connected to the output side of the operational amplifier 2 via S9. Either the former stage or the latter stage of R4 may be used. The output of the negative feedback circuit 12 is connected to the input side of the operational amplifier 2 via diodes D1 and D2. The diodes D1 and D2 are connected in parallel with their polarities reversed. Each reverse polarity is also called a forward direction and a reverse direction of the diode current.

In the normal state before switching (FIG. 2H), S8 is on (FIG. 2C), S9 is off (FIG. 2D), and the output voltage V2 of the amplifier 4 of the negative feedback circuit 12 is 0V (FIG. 2F). Has become. Therefore, the diodes D1 and D2 are off, and the output voltage Vo of the system when S6 is on.
Is Vo = −R3 · E / R1. In the example above,
Vo = 0.01V.

At the time of switching t _H (FIG. 2H), first, S8 is turned off (FIG. 2C), and the output voltage Vo of the system is held by the capacitor C1 to continuously output the voltage of Vo (FIG. 2G). Since the system is open, the output voltage V1 of the operational amplifier 2 is about to be saturated (FIG. 2E). Subsequently, when S9 is turned on (FIG. 2D), the negative feedback circuit 12 starts to operate, the output voltage V2 of the amplifier 4 moves, and the diode D1 or D2
Turn on. As a result, negative feedback is applied to the operational amplifier 2, and V1 returns to 0V again. After that, S6 is turned off (Fig. 2
A), by turning on S7 (FIG. 2B),
Switch the input resistance and change the output range.

Thereafter, when S8 is turned on (FIG. 2C) and S9 is turned off (FIG. 2D), the output voltage V1 of the operational amplifier 2 is 0 V, and the voltage at the moment when S8 is turned on becomes almost zero.
10E, the generation of spike noise P as shown in FIG. 10E is prevented, and the output voltage of the system of the system is V
A voltage given by o = -R3.E / R2 is output (FIG. 2G). In the above example, Vo = 0.1V
Is switched to.

FIG. 3 shows the maximum output voltage of the system system having this voltage hold circuit 10 and the negative feedback circuit 12.
This is a circuit configuration suitable for a voltage generator of 0 V or more. Since the output voltage V3 of the voltage hold circuit 10 may be about 10 V, the withstand voltage of the voltage hold capacitor C1 is expressed by the following equation.
It may be 0V. Then, the output voltage V3 of the voltage hold circuit 10 is input to the high-voltage operational amplifier 15. Since the driving power supply of the high-voltage operational amplifier 15 is several hundred volts or more, an IC (integrated circuit) cannot be used. The output voltage Vo is fed back to the first-stage operational amplifier 2 via a feedback resistor R3.

The configuration of FIG. 4 does not switch the output voltage generation range of the system between the input resistors R1 and R2, but only the input resistor R1 and switches the feedback resistors R31 and R32. The output voltage Vo is Vo = −R31 · E
/ R1 and Vo = −R32 · E / R1. In the claims of this specification, R31 and R32 and a plurality of R3i are collectively referred to as R3. Further, the switch S9 for turning on / off the negative feedback circuit 12 can be operated by being connected in parallel to the feedback resistor R7 of the operational amplifier 4. When S9 is turned on, it becomes a voltage follower, and the diodes D1 and D2 are off. When S9 is turned off, the negative feedback circuit 12 amplifies the input voltage by several tens and
1 or D2 is turned on to configure the negative feedback circuit 12.

FIG. 5 is a configuration diagram of an example in which the operational stages are composed of three operational amplifiers 2, 5, and 3, respectively. In this case, the operational amplifier 2, the operational amplifier 5, and the operational amplifier 3 may be configured as inverting amplifiers.
The two operational amplifiers 4 have a non-inverting amplifier configuration. The operational amplifier of the voltage hold circuit 10 is five. Further, a switch S9 for turning on / off the negative feedback circuit 12 may be connected to the ground side of the input terminal of the operational amplifier 4 to be operated. When S9 is turned off, it becomes a voltage follower, and the diodes D1 and D2 are off. When S9 is turned on, the negative feedback circuit 12 amplifies the input voltage and turns on D1 or D2 to form the negative feedback circuit 12.

FIG. 6 shows the operational amplifier 5 and the resistor R4 of FIG.
FIG. 3 is a configuration diagram of an example in which is replaced with an inverting voltage-current converter composed of transistors T1 and T2 and a plurality of resistors. Since the output is a current, there is no resistor R4. Generally, the design of an amplifier is based on an operational amplifier IC called an operational amplifier.
Although it is easy to implement the configuration and the performance is good, there is a case where the configuration of the system cannot be satisfied only by the IC Op amplifier. In this case, the configuration is often made using individual transistor circuits. The present invention is effective even in such a case.

Up to now, a plurality of switches (S6, S7) for switching the output voltage (Vo) and resistors (R1, R2, R
Although 3i) has been described with two types, the present invention is not limited to this, and a wide range may be switched with three or more types of switches and resistors.

[0023]

As described above in detail, the present invention provides a method for switching the range of generation of the output voltage Vo by using a switch.
Voltage holding circuit 10 using operational amplifier 3, voltage holding capacitor C1, and phase compensation resistor R5 in the system
As a result, the spike-like noise P generated in the voltage generator for preventing the output voltage Vo from being excessively large or too small can be reduced.

As a means for switching the voltage generation range, t
_The negative feedback circuit 12 that drives only _H is connected to the voltage hold circuit 10
Between the input and output terminals of the operational amplifier. In addition, the voltage hold circuit 10 was driven at a voltage that is easy to use, and a high-voltage operational amplifier 15 of several hundred volts or more was provided at the subsequent stage to switch the high-voltage generation range.

That is, a single voltage generator can switch the voltage range from several mV to 1000 V without generating excessive voltage, undervoltage or spike noise P. Therefore, the effect of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a basic embodiment of the present invention.

FIG. 2 is a timing chart of the circuit of FIG. 1;

FIG. 3 is a configuration diagram of another embodiment of the present invention.

FIG. 4 is a configuration diagram of another embodiment of the present invention.

FIG. 5 is a configuration diagram of another embodiment of the present invention.

FIG. 6 is a configuration diagram of another embodiment of the present invention.

FIG. 7 is a basic configuration diagram of a conventional example.

FIG. 8 is a configuration diagram obtained by improving the configuration of FIG. 7 of the conventional example.

FIG. 9 is an ideal timing chart of the circuit of FIG. 8;

FIG. 10 is an actual waveform diagram of the circuit of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reference voltage generator 2, 3, 4, 5 Operational amplifier 6, 7, 8, 9 Switch 10 Voltage hold circuit 11 Output terminal 12 Negative feedback circuit 15 High voltage operational amplifier S Switch R Resistance R1, R2, R4, R6, R9 Input resistor R3, R31, R32, R7, R10 Feedback resistor R5 Phase compensation resistor C1 Voltage holding capacitor D1, D2 Diode

Claims (3)

[Claims] 1. A system for feeding back an output voltage (Vo) to an input terminal of an operational amplifier (2) in a first stage via a feedback resistor (R3), wherein a generation range of an output voltage (Vo) is controlled by a plurality of switches. (3) An operational amplifier (3) which switches off a system-related switch (S8) and maintains an output voltage (Vo) when a voltage generation range is switched (t _H ) in the voltage generator switchable in (S6, S7). A voltage holding circuit (10) composed of a voltage holding capacitor (C1) and a phase compensation resistor (R5); and a voltage generation range between the input / output terminals of the operational amplifier of the voltage holding circuit (10). A negative feedback circuit (12) for setting the output voltage (V1) of the operational amplifier of the voltage hold circuit (10) to zero only at (t _H ). 2. The negative feedback circuit (12) includes a switch (S
9), an input resistor (R6), a feedback resistor (R7), an operational amplifier (4), connected between the output terminal of the operational amplifier (4) and the input terminal of the operational amplifier of the voltage hold circuit (10). A negative feedback circuit comprising a pair of diodes (D1, D2) connected in opposite polarities and having an amplification degree by turning on the S9 only at the time of switching (t _H ) in which the voltage generation range is switched by a plurality of switches. A negative feedback circuit (12) which is configured to turn off S9 during normal times other than switching (t _H ) to form a voltage follower circuit and to turn off both the diode (D1) and the diode (D2). The voltage generator according to claim 1, wherein: 3. The voltage generator according to claim 1, further comprising a high-voltage operational amplifier (15) of several hundred volts or more provided at a stage subsequent to the voltage hold circuit (10), and an output of the high-voltage operational amplifier (15). A voltage generator for feeding back a voltage (Vo) to an input terminal of an operational amplifier (2) via a feedback resistor (R3).