JPH06209219A - Amplifier - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an amplifier compatible with the frequency of the entire band without amplifying the DC offset voltage superimposed on the minute input signal and without damaging the waveform of the minute input signal. [Structure] A non-inverting amplifier is composed of the operational amplifier 1, the resistor 6 and the resistor 7, the capacitor 10 is connected between the reference potential point 5 and the non-inverting input terminal 12 of the operational amplifier 9, and the signal output terminal 3 and the operation are connected. The switch 11 was connected between the non-inverting input terminal 12 of the amplifier 9. Further, the output terminal 14 of the operational amplifier 9 and the inverting input terminal 13 are connected to form a buffer circuit, and the output terminal 14 of the operational amplifier 9 is connected to the resistor 7 to form a feedback loop.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention has a function of amplifying only a minute input signal component without amplifying a DC offset voltage superimposed on a minute input signal in the amplification of minute signals such as various sensor signals. It relates to an amplifier.

[0002]

2. Description of the Related Art Conventionally, a non-inverting amplifier or an inverting amplifier has been used for amplifying a minute signal.

A conventional amplifier will be described below with reference to the drawings. FIG. 3 is a circuit diagram showing a conventional amplifier. In FIG. 3, 1 is an operational amplifier, 2 is a signal input terminal, 3 is a signal output terminal, 4 is an inverting input terminal of the operational amplifier 1, 5 is a reference potential point (ground point), 6 and 7 are resistors, and 8 is a capacitor. Is. The resistor 6 is connected between the output terminal 3 and the inverting input terminal 4 of the operational amplifier 1, the resistor 7 and the capacitor 8 are connected in series between the operational amplifier 1 and the reference potential point 5, and the signal input terminal 2 is connected as a signal. A non-inverting amplifier that receives an input and outputs a signal from the signal output terminal 3 is configured.

Regarding the amplifier configured as described above,
The operation will be described below. When the gain of the amplifier shown in FIG. 3 is G, the gain G is given by the equation 1.

[0005]

[Equation 1]

[0006] However, V _IN: Input signal voltage of the signal input terminal 2 V _OUT: signal output terminal 3 of the output signal voltage R _6: the resistance value R ₇ of resistor 6: resistance C ₈ of the resistor 7: capacity of the capacitor 8 S: Variable (S = jω) When a minute input signal is input to the signal input terminal 2, from the equation 1, the DC component of the input signal is S = 0, the gain G is G = 1, and the amplifier of FIG. Operates as a buffer circuit. At this time, the capacitor 8 is charged with the DC component of the input signal and the potential difference between the reference potential point 5 as a DC offset voltage. Also, regarding the AC component of the input signal, FIG.
1 operates as an amplifier having a gain G shown in the equation (1).

Therefore, the amplifier of FIG. 3 has a high bandpass characteristic, and has a function of amplifying only a minute input signal without amplifying the DC offset voltage superimposed on the minute input signal at the frequency of the passband. Operates as an amplifier.

[0008]

However, in the above-mentioned conventional amplifier, since the amplifier has a high bandpass characteristic, it is used in the case of handling a voltage change signal which is not a positive / negative target such as a differential change type sensor signal, or in a single shot. When handling a triangular wave signal or the like, at a frequency lower than the cutoff frequency, the signal waveform of the output signal becomes completely different from that of the input signal, or the waveform responsiveness of the output signal deteriorates. Also,
In order to improve the waveform responsiveness, it is necessary to set a large time constant, and in the case of an integrated circuit, there is a problem that the capacitance of the capacitor becomes large and it is difficult to incorporate it in a chip.

The present invention solves the above-mentioned conventional problems, and an object thereof is to provide an amplifier capable of removing a DC offset voltage without damaging an input signal waveform even in a low band.

[0010]

In order to achieve the above object, the amplifier of the present invention has the following configuration.
That is, a first amplifier having a non-inverting input terminal, an inverting input terminal and an output terminal, a second amplifier having a non-inverting input terminal, an inverting input terminal and an output terminal, a non-inverting input terminal of the first amplifier and A signal input terminal and a signal output terminal respectively connected to the inverting input terminal, a first resistor connected between the signal output terminal and the inverting output terminal of the first amplifier, and an inverting input terminal of the first amplifier And a second resistor connected between the second amplifier and the output terminal of the second amplifier, a switch connected between the signal output terminal and the second amplifier, and a non-inverting input terminal of the second amplifier and the reference. A capacitor connected between the point and a point, and the output terminal of the second amplifier is connected to the inverting input terminal of the second amplifier.

[0011]

With the above-described structure, when the switch is in the on state, the direct current component in the no-signal state is extracted and the capacitor is charged, and when the switch is in the off state, impedance conversion is performed by the second operational amplifier forming the buffer circuit. The DC offset voltage stored in the capacitor serves as the reference potential of the non-inverting amplifier composed of the first and second resistors and the first operational amplifier, and only the AC component of the minute input signal can be amplified.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an amplifier according to an embodiment of the present invention. In FIG. 1, 9 is an operational amplifier, 1
0 is a capacitor, 11 is a switch, 12 and 13 are the non-inverting input terminal and inverting input terminal of the operational amplifier 9, respectively.
Reference numeral 14 is an output terminal of the operational amplifier 9. In addition, 1 is an operational amplifier, 2 is a signal input terminal, 3 is a signal output terminal, 4 is an inverting input terminal of the operational amplifier 1, 5 is a reference potential point (ground point), and 6 and 7 are resistors. Is the same as. The operational amplifier 1, the resistor 6 and the resistor 7 constitute a non-inverting amplifier, and the reference potential point 5 and the non-inverting input terminal 1 of the operational amplifier 9
The capacitor 10 is connected between the signal output terminal 3 and
The switch 11 is connected between the non-inverting input terminal 12 of the operational amplifier 9 and the operational amplifier 9. Further, the output terminal 14 of the operational amplifier 9 and the inverting input terminal 13 are connected to form a buffer circuit, and the output terminal 14 of the operational amplifier 9 and the resistor 7 are connected to form a feedback loop. .

The operation of the amplifier of the present embodiment constructed as above will be described. First, a signalless potential (DC offset voltage of a circuit or the like when connected in the previous stage) is input to the signal input terminal 2. At this time, when the switch 11 is turned on, the potential of the signal output terminal is negatively fed back to the operational amplifier 1 via the switch 11 and the operational amplifier 9 forming the buffer circuit. Then, the potential of the signal output terminal, the output terminal 14 of the operational amplifier 9 and the inverting input terminal of the operational amplifier 1 become the same potential, and the potential difference between the reference potential point 5 and the signal output terminal 3 is applied to the capacitor 10 by the DC offset. It is charged as a voltage. Next, the switch 11 is turned off and a minute input signal is input to the signal input terminal 2. Since the DC offset voltage in the non-signal state is stored in the capacitor 10 by turning off the switch 11, the DC offset voltage in the non-signal state is output to the output terminal 14 of the operational amplifier 9 forming the buffer circuit. Is output. Therefore, the minute input signal is amplified with reference to the potential of the DC offset voltage in the signalless state whose impedance is converted by the output terminal of the operational amplifier 9. When the gain of the amplifier shown in FIG. 1 is G'for a minute input signal, the gain G'is given by Equation 2.

[0015]

[Equation 2]

However, V _IN ': input signal voltage of the signal input terminal 1 V _OUT ': signal output voltage of the signal output terminal 3 R ₆ : resistance value of the resistor 6 R ₇ : resistance value of the resistor 7 According to this embodiment, the capacitor 10 is charged with the DC offset voltage in the switch-on state,
The DC offset voltage stored in the switch-off state is impedance-converted by the operational amplifier 9 that constitutes a buffer circuit and acts as a reference potential of the non-inverting amplifier composed of the resistors 6 and 7 and the operational amplifier 1 to obtain the entire band. In, the non-inverting amplifier can be realized, and it is possible to amplify the DC offset voltage superimposed on the minute input signal without amplifying it and without damaging the waveform of the minute input signal. Moreover, the response of the output signal is improved by having the all-band filter characteristic. Further, as shown by the gain G ′ of the equation 2, since the low band frequency can be amplified regardless of the capacity of the capacitor 10, the capacity of the capacitor 10 can be reduced, and the area to be tightened by the capacitor 10 in the integrated circuit can be reduced.

FIG. 2 shows another embodiment of the present invention. In FIG. 2, a resistor 15 is connected between the signal output terminal 3 and the switch 11 so as to have a filter characteristic, so that when the capacitor 10 is charged with the potential in the no signal state, noise is removed and an error in the offset voltage is reduced. It has been given as follows.
It is obvious that the effect of the present invention can be obtained also in the circuit shown in FIG.

[0018]

According to the amplifier of the present invention, the DC offset voltage in the signalless state is charged in the capacitor in the switch-on state, and the DC offset voltage stored in the capacitor in the switch-off state constitutes the buffer circuit. Since it is configured to act as a reference potential of the non-inverting amplifier composed of the first and second resistors and the first amplifier via the second amplifier, a non-inverting amplifier having an all-band filter characteristic can be realized. The DC offset voltage superimposed on the minute input signal is not amplified, and can be amplified without impairing the signal waveform of the minute input signal.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an amplifier according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of an amplifier according to another embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional amplifier.

[Description of symbols] 1 operational amplifier 2 signal input terminal 3 signal output terminal 5 reference potential point (ground point) 6, 7 resistance 9 operational amplifier 10 capacitor 11 switch

Claims (1)

[Claims] 1. A first amplifier having a non-inverting input terminal, an inverting input terminal and an output terminal, a second amplifier having a non-inverting input terminal, an inverting input terminal and an output terminal, and a non-inverting element of the first amplifier. An inverting input terminal and a signal input terminal and a signal output terminal respectively connected to the inverting input terminal; a first resistor connected between the signal output terminal and the inverting output terminal of the first amplifier; A second resistor connected between the inverting input terminal of the first amplifier and the output terminal of the second amplifier; a switch connected between the signal output terminal and the second amplifier; An amplifier comprising a capacitor connected between a non-inverting input terminal of the second amplifier and a reference point, the output terminal of the second amplifier being connected to the inverting input terminal of the second amplifier.