JPS58219806A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To shorten rise time up to steady operation status by inserting a transistor (TR) to charge a capacitor for a feedback circuit quickly between the base of a TR constituting the feedback circuit of a differential amplifier and a power supply. CONSTITUTION:An input is applied to the base of a TR Q1 constituting the differential amplifier and a part of an output of an output TR Q4 connected to the post-stage is fed back to the base of the other TR Q2 through resistors R4, R5 and a capacitor C4. A TR Q7 to be controlled by the output of the TR Q4 is conneced between the base of the TR Q2 and Vcc. At the moment when the TR Q4 is turned on after turning a power supply SW on, the TR Q7 is turned on and Vcc is applied to the capacitor C4 immediately through the TR Q7 and R5. Consequently, the base potential of the TR Q5 constituting the differential amplifier can be quickly turned to a half of the Vcc and the whole amplifier circuit can be turned to normal operation status immediately.

Description

[Detailed Description of the Invention] The present invention relates to a low frequency amplification circuit used in various 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 can quickly be brought into a normal operating state. It is something to do.

2. Generally speaking, amplifier circuits used in take recorders are required to be in a normal operating state as soon as the record button or playback button is pressed and the power is turned on. This type of amplifier circuit does not always start up quickly when the power is turned on, and the problem is that the first portions of recording and playback are 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, Dl, D2. R1.R2 are a diode and a resistor, respectively, which constitute a voltage source for obtaining a voltage of % of the power supply voltage Vcc. Resistors R1, R2 and diode D2 are each connected in series. Ql and Q2 are transistors constituting a differential amplifier whose emitters are connected to each other, and the base of one transistor Q1 is connected to the above voltage via a resistor R3. , and at the same time, it is connected to the signal input terminal a via the coupling capacitor C1. Q3. D3 are a transistor and a diode, respectively, which constitute a current mirror circuit, and transistors Q1, . Connected to the collector of Q2.

Q4 is an output transistor whose base is connected to the collector of one of the transistors Q1 constituting the differential amplifier, and whose output end, that is, the collector, is connected to the output terminal S via a coupling capacitor C3. Q6
．． Q6 is a constant current source transistor whose base is connected to the connection point of the resistor R2 and the diode D2, which constitute a voltage source, and the collector of one of the transistors Q6 is connected to the transistor Q1.Q6 which constitutes a differential amplifier. The collector of the other transistor Q6 is connected to the common emitter of the transistor Q2, and the collector of the output transistor Q4 is connected to the common emitter of the transistor Q2. In addition, C2 is an output transistor Q4
A phase compensation capacitor is connected between the collector of the transistor Q1 and the collector of one transistor Q1 forming the differential amplifier. R4, R5, and C4 are resistors and capacitors forming an AC and DC feedback circuit.

Q7 is controlled by the output of an output transistor Q4 connected between the power supply line and the base of the other transistor Q2 constituting the differential amplifier. A transistor C6 is a capacitor connected between the power supply terminal Vcc and ground. , SW is a power switch.

In the above embodiment, it is assumed that transistor Q7 does not exist. 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 the power switch SW is turned on, the diode D1. A predetermined current flows through a voltage source made up of D2 resistors R1 and R2. Therefore, a voltage of % of the power supply voltage Vcc appears at the connection point between the resistor R1 and the resistor R2 constituting the voltage source at the same time as the power switch SW is turned on. The voltage that appears here is applied to one transistor Q that constitutes a differential amplifier via a resistor R3.

Applied to the base of page 6. The base of the other transistor Q2 constituting the differential amplifier is connected to the resistor R6 constituting the feedback circuit.
, and is grounded via capacitor C4, and in this state, since capacitor C4 is not yet charged, it is almost at ground potential. Therefore, one transistor Q1 constituting the differential amplifier is almost completely turned on, and the output transistor Q4 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. When the output transistor Q4 is almost completely turned on, the collector potential of the output transistor Q4 is almost close to the power supply voltage Vcc. Therefore, capacitor C4 starts charging with this voltage via resistors R4 and R6. As charging of the capacitor C4 progresses and the base potential of the other transistor Q2 constituting the differential amplifier reaches % of the power supply voltage Vcc, the same as the base potential of the one transistor Q1, the differential amplifier enters a normal operating state. , output transistor Q4 is also normal 6
The vane is in working condition. In other words, if there is no transistor Q7, at least a certain period of time determined by resistors R4, R, and capacitor C4 is required for the base potential of the other transistor Q2 constituting the differential amplifier to reach % of the power supply voltage Vcc. This will cause a delay in the amplifier circuit returning to its normal operating state.Specifically, considering the gain of the entire amplifier circuit, the resistor R4 should be several tens of kilohms, and the resistor R6 should be a capacitor C of several tens to hundreds of ohms.
4 is often selected to be several hundred μF, so it takes several seconds for the amplifier circuit to become in a normal operating state.

However, according to the above embodiment, since the transistor Q7 is inserted, the transistor Q7 is turned on at the moment the output transistor Q4 is turned on, and the transistor Q7. The power supply voltage Vcc is immediately applied via the resistor R6.
is applied to the capacitor C4, the base potential of the other transistor Q5 constituting the differential amplifier can be quickly brought to % of the power supply voltage Vcc. That is,
In this case, on page 7, when transistor Q7 is in an operating state where sufficient charging current can flow, the constant (time constant determined by resistor R6 and capacitor C4) and the base-emitter voltage of transistor Q7 are 0.7V. becomes below, transistor Q7
Since the time constant for capacitor C4 to charge up to the potential of power supply voltage VccO% is determined by the difference between the time constant (time constant determined by resistor R4 and R6 capacitor 18) when transistor Q7 becomes inactive, The entire amplifier circuit can be put into a normal operating state much faster than in the case where there is no amplifier. For example, the values of resistors R4 and R6 are several tens of kilohms, several tens to hundreds of ohms) capacitor C4
If the value of is selected to be several 1001 tF, the time required to reach the normal operating state can be reduced to approximately several 100 milliseconds, which is approximately one-tenth of the time required without transistor Q7.

As is clear from the above embodiments, the amplifier circuit of the present invention can significantly shorten the time required to reach a steady operating state with a simple configuration, and is extremely advantageous in practice.

1 network I] U38-219806 count)

[Brief explanation of drawings]

The figure is an electrical wiring diagram of one embodiment of the amplifier circuit of the present invention. D~D...Diode, QlS-o7o...
3 Transistor, R++R...Resistance, C1 to C6...
5 Condenser (II-1SW... Power switch f,
1 me...Input terminal, b...Output terminal. Name of agent Patent attorney Satoshi Nakao (Male) and one other person Written amendment 1 Description of the case 1982 Patent Application No. 10185J3 2 Name of the invention Amplifier circuit 3 Person making the amendment Relationship with the case Patent applicant 2 Address: 1006 Kadoma, Kadoma City, Osaka Prefecture
Name (582) Matsushita Electric Industrial Co., Ltd. Representative Toshihiko Yamashita 4 Agent 571 Address 6, Matsushita Electric Industrial Co., Ltd., 1006 Oaza Kadoma, Kadoma City, Osaka Contents of the amendment (1) Specification page 7 Correct "time, constant" in the second line to "time constant". (2) On page 7, line 7, "by the difference between" is corrected to "by both."

Claims (1)

[Claims] An input signal is applied to the base of one of the transistors constituting the differential amplifier, and a feedback circuit consisting of a resistor and a capacitor is connected to the base of the other transistor, and a portion of the output of the output transistor connected to the latter stage of the differential amplifier is connected to the base of the other transistor. and another transistor controlled by the output of the output transistor is connected between the base of the other transistor constituting the differential amplifier and the power supply, and the above-mentioned An amplifier circuit configured to quickly charge a capacitor via the above-mentioned another transistor when power is turned on.