JPS6116604A - Amplifying circuit - Google Patents

Abstract

PURPOSE:To improve the rising operation of the amplifying circuit by charging the feedback capacitor of a feedback circuit speedily through a diode when a power source part turns on. CONSTITUTION:A voltage V0 from a terminal 101 is applied from a terminal 121 to the feedback circuit 51 through the load resistance 11 of an operational amplifier 1 and a terminal 107. Consequently, it is applied to the feedback capacitor 63 through charging impedance 71, i.e. a diode 67 and a current limiting resistance 69 and then the feedback resistance 61 of feedback impedance 65, so that a charging current flows to the feedback capacitor 63. Then when the feedback 63 is charged until its terminal voltage, i.e. voltage at a terminal 125 rises up to about 1/2V0, the voltage at a terminal 105 of the operational amplifier 1 connected to the terminal 125, i.e. base voltage of a transistor (TR)9 also rises up to about 1/2V0 and then the TR9 turns on, so that the operating current of the TR9 flows from the terminal 101 to the load resistance 11 and an emitter resistance 7. Then, the collector voltage of the TR9 drops to about 1/2 V0 and this circuit amplifies a specific AC signal.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to an amplifier circuit that improves startup operation when the power supply section is turned on in a circuit using an operational amplifier driven by a power supply section with a single output polarity. It is.

BACKGROUND ART Conventionally, in a circuit that uses an operational amplifier driven by a power source with a single output polarity and amplifies the AC component without amplifying the DC component, the output of the operational amplifier is The DC component of the output signal is negatively fed back from the terminal to the inverting input terminal, and the AC component of the output signal is divided into a predetermined value and fed back negatively. In other words, this negative feedback is caused by a feedback capacitor connected between the inverting input terminal of the operational amplifier and ground,
This is performed by a feedback circuit configured with a predetermined feedback impedance connected between the inverting input terminal and the output terminal. Therefore, the power supply section turns on and the power supply voltage vo
When is applied to the operational amplifier, the non-inverting input terminal becomes a DC voltage of about 172 Vo through the bias resistor. and,
The output terminal becomes a DC voltage of approximately vo, and this DC voltage passes through a feedback circuit and charges a feedback capacitor connected between the inverting input terminal and the ground via a feedback resistor.

As this feedback capacitor is charged, the DC voltage at the inverting input terminal changes from 0 to 1/2 VO. Then, the output terminal is reduced to a DC voltage of about 1/2Vo and becomes in a steady state, and this amplifier circuit enters a state in which it performs a predetermined amplification operation. That is, there is a drawback that the input signal applied to the non-inverting input terminal is not amplified normally until the feedback capacitor described above is completely charged.

DISCLOSURE OF THE INVENTION The present invention provides a feedback impedance connected between an output terminal and an inverting input terminal of an operational amplifier driven by the output voltage of a power supply section with a single output polarity, and a feedback resistor between the inverting input terminal and ground. In an amplifier circuit having a feedback circuit consisting of a feedback capacitor connected to It is something to do.

Since the present invention is configured as described above, when the power supply section is turned on, the feedback capacitor of the feedback circuit is charged through the diode more rapidly than in the past, so that the amplifier circuit according to the present invention The operation is better than before.

Best mode for carrying out the invention Embodiments of the present invention will be described below with reference to the drawings.

Referring to the circuit diagram of the amplifier circuit according to the present invention in FIG.
1 is an operational amplifier having a power supply voltage application terminal 101, a non-inverting input terminal 103, an inverting input terminal 105, and an output terminal 107. The operational amplifier 1 has a first transistor 3, a first load resistor 5 is connected between its collector and a terminal 101, its base is connected to a terminal 103, and its emitter is connected via an emitter resistor 7. and connected to ground.

Further, the operational amplifier 1 has a second transistor 9, a second load resistor 11 is connected between its collector and a terminal 101, its collector is connected to a terminal 107, and its base is connected to a terminal 105, Its emitter is connected to ground via an emitter resistor 7. And terminal 1
07 is the signal output terminal 1 via the coupling capacitor 41
It is connected to 23.

21 is a power supply section, one output terminal 111 is grounded, and the other output terminal 113 is connected to the terminal 101 of the operational amplifier 1;
It is connected to one terminal of the first bias resistor 31. The other terminal of the resistor 31 is the terminal 1 of the coupling converter 1.
03 is connected to the other terminal of a second bias resistor 35, one terminal of which is connected to ground. 51 is a feedback circuit and its input terminal.

121 is connected to the output terminal 125 via a first feedback impedance 57 composed of a feedback resistor 53, and is composed of a feedback resistor 61 and a feedback capacitor 63 connected in series between the terminal 125 and the ground. A second feedback impedance 65 is connected. And terminal 12
A charging impedance 71 is connected between 1 and 125, in which a diode 67 and a current limiting resistor 69 are connected in series in the direction in which the charging current of the capacitor 63 flows.

Next, the operation will be explained. When a power switch (not shown) is turned on from the off state, a positive polarity voltage (2) with a single output polarity is output from the terminal 113 of the power supply unit 21.

is output with reference to the ground voltage of the terminal 111, and is applied to the terminal 101 of the operational amplifier l and one terminal of the bias resistor 31. Then, the voltage ■
The voltage o is divided into approximately 1/2 and applied to the base of the transistor 3 via the terminal 103 of the operational amplifier 1, and the transistor 3 changes from off to on. The operating current of transistor 3 flows through. On the other hand, the voltage vo is applied from the terminal 101 to the operational amplifier 1.
via load resistance 11 and terminal 107, terminal 121
is applied to the feedback circuit 51. As a result, the charging current is applied to the feedback capacitor 63 via the charging impedance 71, that is, the diode 67, the current limiting resistor 69, and the feedback resistor 61 of the feedback impedance 65, and a charging current flows to the feedback capacitor 63. Then, when the feedback capacitor 63 is charged and its terminal voltage, that is, the voltage at the terminal 125 rises to about 1/2 Vo, the terminal 105 of the operational amplifier 1 connected to the terminal 125, that is, the base voltage of the transistor 9, also rises to about 172 Vo. As a result, the transistor 9 changes from off to on, and the operating current of the transistor 9 flows from the terminal 101 to the load resistor 11 and the emitter resistor 7. In doing so, the collector of transistor 9 has a voltage v
o to approximately 1/2 Vo, and the amplifier circuit according to the present invention is in a state where it can perform a predetermined AC signal amplification operation. That is, the AC component input signal Δ applied to the terminal m is applied to the base of the transistor 3 via the coupling capacitor 33, is amplified, and appears at both ends of the emitter resistor 7. This signal is then applied to the base of transistor 9 and amplified, and the phase is inverted and the load resistor 110
Appears at both ends, that is, between terminal 107 and ground. On the other hand, this signal is applied to the terminal 121 of the feedback circuit 51, given a feedback rate determined by the feedback impedances 57 and 65, and becomes a predetermined feedback signal. Transistor 90 from 105
A negative feedback signal is applied to the pace. therefore,
The signal at the load resistor 11, that is, at the terminal 107 becomes a signal having a predetermined voltage and frequency characteristic, and is outputted to the terminal 123 via the coupling capacitor 41. Here, in the feedback circuit 51, the magnitude of the signal applied to the diode 67, that is, the output signal of the terminal 123, is adjusted so that the magnitude of the signal applied to the diode 67 is about 0.6 V or less, which is the forward voltage drop of the diode 67, or less. The size needs to be set. In addition, in the feedback circuit 51, the feedback impedance 6
Since the direct current component of the signal at the terminal 121 is insulated from the ground by the feedback capacitor 63 of No. 5, it is output from the terminal 125 without attenuation. therefore,
In the transistor 9 of the operational amplifier 1, the DC component is subjected to negative feedback with a value close to 100%, so no DC component appears at the terminals 107 and 123. In addition to 71, another third transistor 81 is used, a base resistor 83 is connected between its base and the input terminal 121 of the feedback circuit 51, and a current limiting resistor 85 is connected between its collector and the power supply voltage application terminal 131. and its emitter and output terminal 1
25, a first feedback impedance 57 may be connected between the input terminal 121 and the output terminal 125, and a second feedback impedance 65 may be connected between the output terminal 125 and the ground. Regarding the operation, as in the previous embodiment, when the power switch is turned on from off, the base voltage of transistor 81 is about vO and the emitter voltage is about □V. It is carried out via the Collector Emituta Road. Then, when the terminal voltage of the feedback capacitor 63 approaches about 1/2 Vo, the transistor 9 changes from off to on, and the voltage at terminals 107 and 121 changes from o to about 1/2 Vo.
/2Vo, the emitter and base voltages of the transistor 81 become approximately 1/2Vo, and the transistor 81 changes from on to off operation. Since the charging current of the far-field capacitor is not passed through a feedback impedance but through a charging impedance formed by a series connection of a diode, transistor, etc. and a current-limiting resistor, the start-up operation can be made better than in the past.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an amplifier circuit according to the present invention. 1... Operational amplifier, 103... Non-inverting input terminal, 1
05... Inverting input terminal, 107... Output terminal, 51
...Feedback circuit, 57...Feedback impedance, 63
...Feedback capacitor, 67.81, 83.85...
・Charging impedance 0

Claims (1)

[Claims] An input signal is applied to a non-inverting input terminal of an operational amplifier driven by a power supply section with a single output polarity, and the output terminal of the operational amplifier is connected to the inverting input terminal by a feedback capacitor of a feedback circuit. In a circuit in which a DC component of an output signal and an AC component divided into a predetermined value of the output signal by a feedback impedance are negatively fed back, the feedback capacitor is connected between the output terminal and the feedback capacitor. An amplifier circuit comprising a charging impedance connected in a direction in which a charging current flows.