JPS58215105A - Amplifying circuit - Google Patents

Abstract

PURPOSE:To decrease a time remarkably from the application of power supply to the normal operating state, so-called leading time, by applying a bias voltage a half the power supply voltage to bases of both transistors (TR) constituting a differential amplifier via a resistor respectively, for forming a capacitor constituting a feedback circuit so as to be charged quickly via a resistor at the application of power supply. CONSTITUTION:A voltage a half a power supply voltage Vcc obtained from a voltage source is impressed to a capacitor C4 immediately via a resistor R6. Thus, a base unit of the other TRQ5 constituting a differential amplifier is brought into a half the power supply voltage Vcc quickly and the entire amplifying circuit is brought into the normal operating state very quickly in comparison with the case without the resistor R6. For example, in using several kilohms of the resistor R6, the time becoming the normal operating state is about several hundreds msec, allowing to reduce the time to about 1/10 in comparison with the case without the resistor R6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low frequency amplification circuit used in various types of audio equipment such as tape recorders, and an object of the present invention is to provide an excellent amplification circuit that has a simple configuration and quickly rises to a normal operating state. This is the purpose.

Generally, an amplifier circuit used in a tape recorder is required to be in a normal operating state as soon as the record button or play button is pressed and the power is turned on. 1 more than before
This type of amplifier circuit currently in use had the problem that it did not always go up quickly when the power was turned on, and the first portions of both recording and playback would be interrupted.

The present invention eliminates the above-mentioned conventional drawbacks and provides an excellent amplifier circuit that can significantly shorten the so-called rise time from power-on to normal operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The amplifier circuit of the present invention will be described below with reference to drawings of an embodiment. In the figure, D1 to D4. R1R2, Ql
, Q2 are diodes, resistors, and transistors that constitute a power source for obtaining the negative voltage of the power supply voltage vcc, respectively, and the diodes D1 . Resistor R1゜Diode D2. D
3. The resistor R2 and the diode D4 are connected in series with each other, and the transistor Q1. Connected to the base of Q2. Q4. Q6 are transistors whose emitters are connected to each other and constitute a differential amplifier, and the base of one transistor Q4 is connected via a resistor R3 to the transistors Q1 . connected to the emitter of Q2, and at the same time via the coupling capacitor C1 to the signal input terminal a.
It is connected to the. C3 and <- are transistors forming a current mirror circuit, respectively.

transistors Q4 . Connected to the collector of Q5. The base of C7 constitutes the above differential amplifier.

This is an output transistor connected to the collector of one transistor Q4, and its output terminal, that is, the collector, is connected to the output terminal S via a coupling capacitor C3. C6 and C8 are constant current source transistors whose bases are connected to the connection point of the resistor R2 and the diode D4, which constitute a voltage source, and the collector of one of the transistors Q6 is connected to the transistor Q which constitutes a differential amplifier.
4. The other transistor Q is connected to the common emitter of Q6.
The collectors of the transistors 8 and 8 are respectively connected to the collectors of the output transistors Q7. Note that C2 is a phase compensation capacitor connected between the collector of the output transistor Q7 and the collector of one transistor Q4 forming the differential amplifier, R4 and R6C4 are resistors forming the AC and DC feedback circuits, The capacitor R6 is a transistor Q1. which constitutes a voltage source. A resistor is connected between the emitter of Q2 and the base of the other transistor Q5 constituting the differential amplifier, C5 is a capacitor connected between the power supply terminal cc and ground, and SW is a power switch.

In the above implementation row, it is assumed that there is no resistor R6.

If the power switch Sw is turned on in this state, the entire amplifier circuit enters a normal operating state through the following process. That is, when you turn on the power switch SW, first,
Diodes D1 to D4, resistors R1, R2, transistor Q1. A predetermined current flows through the voltage source made up of Q2. Therefore, the transistors forming the voltage source, JQ4. At the connection point of C2, the power supply voltage V is applied at the same time as the power switch SW is turned on.
A Mug from cc appears. The voltage t appearing here is applied via the resistor R3 to the base of one transistor Q4 constituting the differential amplifier. The base of the other transistor Q6 constituting the differential amplifier is grounded via a resistor R5 and a capacitor C4 constituting a feedback circuit, and in this state is almost at ground potential unless the capacitor C4 is charged yet. Therefore, one transistor Q4 constituting the differential amplifier is almost completely turned on, and the output transistor Q7 is also almost completely turned on. Therefore, in this state, even if a signal is applied from the input terminal a, there is almost no amplification effect, and the circuit does not function as an amplifier circuit.

It is in a bad condition. Therefore, capacitor C4 is resistor R4,
Charging will be started by this voltage via R5. The power supply voltage V increases as the charging of capacitor C4 progresses. When C becomes 2, the differential amplifier enters a normal operating state, and the output transistor Q7 similarly enters a normal operating state. In other words, if there is no resistor R6, at least the resistors R4 and R6 are removed before the base potential of the other transistor Q5 constituting the differential amplifier reaches 100% of the power supply voltage vco.
A certain period of time determined by the capacitor C4 is required, which delays the amplifier circuit from reaching its normal operating state.

Specifically, considering the gain of the entire amplifier circuit, the resistor R4 is several tens of kilohms, and the resistor R5 is several tens to several thousand ohms of capacitor C.
4 is often selected to be several 1007 zF, so it takes several seconds for the amplifier circuit to become in a normal operating state.

However, according to the above embodiment, since the resistor R6 is inserted, the power supply voltage vcc obtained from the voltage source.

1 voltage is immediately applied to the capacitor C4 via the resistor R6, and the base unit of the other transistor Q6 constituting the differential amplifier can be quickly set to i of the power supply voltage vcc. The entire amplifier circuit can be put into a normal operating state much faster than when R6 is not provided. For example, if a dKΩ resistor is used as the resistor R6, the time required to reach the normal operating state can be reduced to approximately a100 msec, which is approximately one tenth of the time required without the resistor R6.

In addition, in the embodiment, the smaller the values of the resistors R1, R2, R6, and R5 and the values of the capacitors C4 and C5 are, the shorter the time until the normal operating state is achieved. It is desirable that the values of the resistors R4, R6, and R6 have the following relationship.

R5<R6<R4 As is clear from the examples above, according to the amplifier circuit of the present invention, the time required to reach a steady operating state can be significantly shortened with a simple configuration, which is extremely advantageous in practical use. It is something.

[Brief explanation of the drawing]

The figure is an electrical wiring diagram of one embodiment of the amplifier circuit of the present invention. Gourd pda~~ 0. Diode, Q1-Q8...Transistor, R1-R6--Resistor, C1-C6...Capacitor, SW...Power switch, a - Input terminal,
b...Output terminal.

Claims (1)

[Claims] An input signal is applied to the base of one transistor constituting a differential amplifier, and a part of the output of an output transistor connected to the rear stage of the differential amplifier is connected to the base of the other transistor through a resistor 7. It is configured to feed back via a feedback circuit consisting of a capacitor, and an Iasmi pressure of i of the power supply voltage is supplied to the bases of both transistors constituting the differential amplifier through resistors, respectively, and the feedback circuit An amplifier circuit configured to quickly charge the capacitor constituting the circuit through the resistor when power is turned on.