JPH0787316B2 - Charging circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias circuit for a differential amplifier, and more particularly, to a charging circuit which rises to a constant potential in a short time after power is turned on.

2. Description of the Related Art A typical conventional charging circuit will be described with reference to FIG.

The charging circuit shown in FIG. 2 has a reference voltage circuit formed by resistors R24 and R25 connected in series between the power supply terminal 1 and the ground terminal 2, and a capacitor C21 connected between the intermediate connection point B and the ground terminal 2. The output voltage is set by the resistance ratio of the resistors R24 and R25, and the DC voltage with the ripple component removed is output. The resistors R21 and R22 connected in series between the power supply terminal and the ground terminal 2 divide the power supply voltage. In the differential pair transistors TR1 and TR2 whose emitters are commonly connected, the base of one transistor TR1 is connected to the intermediate connection point B between the resistors R24 and R25, and the base of the other transistor TR2 is connected to the resistors R21 and R22.
Is connected to the intermediate connection point A, and the potential difference between the intermediate connection points A and B is monitored.

The capacitor C21 is for removing the ripple component of the power supply voltage and obtaining a stable DC output voltage. However, when the power supply voltage is turned on, the DC output voltage rises gently with the time constant determined by the resistors R24 and R25 and the capacitance C21.
Therefore, the delay of rising of the DC output voltage is detected by the differential pair transistors TR1 and TR2, the transistor TR2 is made conductive, and the charging current is given to the capacitor C21 via the current mirror circuit composed of the transistors TR3 and TR4. . Then, when the power is turned on, the terminals of the capacitor C21 are rapidly charged to shorten the time for the output voltage to stabilize.

Problems to be Solved by the Invention In such a conventional circuit, the potentials of the intermediate connection points A and B must be set to a state in which they are almost balanced in the steady state. TR1 and TR2 will be conducted even in the steady state other than the transition period of power-on. Then, the operating current becomes a loss current, which is not preferable.

The present invention has been made in view of the above problems, and a charging circuit that applies a charging current to a capacitor only when power is turned on and suppresses unnecessary current consumption while stabilizing a bias to a differential amplifier circuit in a short time. The purpose is to provide.

Means for Solving the Problems In order to achieve the above object, the charging circuit of the present invention includes a first intermediate connection point in which first and second resistors are connected in series between a power supply terminal and a ground terminal, A first capacitor connected between the first intermediate connection point and the ground terminal and a non-inverting input terminal are biased to a potential of the first intermediate connection point via a third resistor and output. In a circuit for biasing an amplifier comprising a differential amplifier circuit in which a fourth resistor is connected between an end and an inverting input terminal, and a second capacitor connected between the inverting input terminal and the ground terminal. , Two diode means for conducting in the forward direction following a potential change at a second intermediate connection point in which fifth and sixth resistances are connected in series between the power supply terminal and the ground terminal, the first intermediate The potential at the connection point and the potential at the inverting input terminal are individually raised in parallel. It is a configuration.

Operation With the above configuration, when the power is turned on, the first capacitor and the second capacitor are rapidly charged so that they have the same potential. Therefore, the potential at the inverting input terminal and the potential at the non-inverting input terminal of the differential amplifier circuit are The time until the balance is reached is shortened, and the operation of the differential amplifier circuit can be stabilized quickly.

Embodiment An embodiment of the charging circuit of the present invention will be described below with reference to the circuit diagram shown in FIG.

In FIG. 1, R11 to R17 are resistors, TR11 is an emitter follower transistor, C1 and C2 are capacitors, D1 and D2 are diodes,
1 is a power supply terminal, 2 is a ground terminal, 3 is an operational amplifier type differential amplifier circuit, 4 is a non-inverting input terminal of the differential amplifier circuit 3, 5 is an inverting input terminal of the differential amplifier circuit 3, and 6 is a differential amplifier. Output terminals of the circuit 3, TR12 and TR13 are PNP transistors at the input stage of the differential amplifier circuit, and TR14 and TR15 are output transistors of the differential amplifier circuit.

The differential amplifier circuit 3 uses the base of the PNP transistor TR12 as the non-inverting input terminal 4 and the base of the PNP transistor TR13 as the inverting input terminal 5 to amplify the signal input from the non-inverting input terminal 4 and The amplified output voltage is output from the output terminal 6 connected to the emitter outputs of TR14 and TR15.

The bias of the non-inverting input terminal 4 of the differential amplifier circuit 3 is the first resistor R1 connected in series between the power supply terminal 1 and the ground terminal 2.
3. A DC voltage determined by the resistance ratio of the second resistor R14 is DC biased from the intermediate connection point B through the third resistor R15. The first capacitor C1 connected between the intermediate connection point B and the ground terminal 2 removes the ripple component of the supply voltage supplied from the power supply terminal 1 to provide a stable DC bias to the non-inverting input terminal 4. give. In addition, the AC input signal is also applied to the non-inverting input terminal 4
Input from.

On the other hand, as for the bias of the inverting input terminal 5, the third resistor R16 is connected between the output terminal 6 and the inverting input terminal 5, and the second capacitor C2 is connected between the inverting input terminal 5 and the ground terminal 2. And output terminal 6
Applies negative feedback to the inverting input terminal 5 like a direct current. For example,
If the potential of the inverting input terminal 5 is low, the output terminal 6 of the differential amplifier circuit 3 rises, and the non-inverting input terminal 4 is fed back by the feedback of the output voltage.
The DC bias of the inverting input terminal 5 is determined such that the potential of the input terminal 5 and the potential of the inverting input terminal 5 are balanced. The resistor R17
Differential amplification circuit 3 by the amount of AC negative feedback by the resistance ratio of R16 and R16.
The AC gain of is set, but when stabilizing the DC bias with the maximum gain, the resistor R17 may be short-circuited.

Next, the fifth resistor R11 and the sixth resistor R12 connected in series between the power supply terminal 1 and the ground terminal 2 always divide the power supply voltage, and the potential at the intermediate connection point A between them is the power supply. It stands up at the same time as the input.

If the potential of the first intermediate connection point B or the inverting input terminal 5 rises slowly when the power supply voltage is turned on, the transistor 11 for the emitter follower becomes conductive and the first transistor via the diode D1
The capacitor C1 is rapidly charged, and the capacitor C2 is rapidly charged through the diode D2. Furthermore, the first intermediate connection point B and the inverting input terminal 5 are raised at the same potential, so that the differential amplifier circuit 3 quickly becomes a stable operation state.

If there is no circuit (TR11, D1, D2) for rapid charging, the time constant for raising the potential of the first intermediate connection point B is the combined resistance of the resistors R13, R14 and the first capacitance C1. Determined by product. The potential of the inverting input terminal 5 is charged into the capacitor C2 through the resistor 16 from the output terminal 6 only after the voltage is output to the output terminal 6 of the differential amplifier circuit 3.
The time constant for raising the potential of is the resistance R16 and the second
Is approximately equal to the product of the capacitance C2 and the time constant. Therefore, it takes time to shift to a stable steady operation without the potential of the inverting input terminal 5 rising easily. First
In this embodiment, the transistor TR11 for emitter follower rapidly charges the emitter output of low impedance so that the capacitors C1 and C2 have the same potential when the power is turned on. Second without depending
Since the capacitance of the differential amplifier circuit is charged, the time until the potential of the inverting input terminal 5 of the differential amplifier circuit and the potential of the non-inverting input terminal 4 are balanced is shortened, and the transition to the bias state in which the differential input can be amplified is swift. As soon as the power is turned on, the differential amplifier circuit is ready for amplification.

EFFECTS OF THE INVENTION As described in detail above, the charging circuit of the present invention rapidly charges the first capacitor and the second capacitor so that they have the same potential when the power is turned on. The time at which the potentials at the ends are balanced can be shortened and the differential inputs can be amplified immediately after power is turned on.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a charging circuit of the present invention, and FIG. 2 is a circuit diagram of a conventional charging circuit. 1 ... power supply terminal, 2 ... ground terminal, 3 ... differential amplifier circuit, 4 ... non-inverting input terminal, 5 ... inverting input terminal, 6 ... output terminal, R11-R17 ... resistance, C1, C2 ... Capacity, TR11 to TR15
...... Transistors, D1, D2 …… Diodes.

Claims (1)

[Claims] 1. A first intermediate connection point for connecting first and second resistors in series between a power supply terminal and a ground terminal, and a first intermediate connection point connected between the first intermediate connection point and the ground terminal. A differential circuit in which a capacitance and a non-inverting input terminal are biased to the potential of the first intermediate connection point via a third resistance, and a fourth resistance is connected between the output terminal and the inverting input terminal. In a circuit for biasing an amplifier including an amplifier circuit and a second capacitor connected between the inverting input terminal and the ground terminal, a fifth and a sixth resistor are connected in series between the power supply terminal and the ground terminal. The potential of the first intermediate connection point and the potential of the inverting input terminal are individually raised in parallel by two diode means which follow the potential change of the second intermediate connection point to be connected and which conducts in the forward direction. Charging circuit characterized by.