JPS60143007A - Low frequency amplifier - Google Patents

Abstract

PURPOSE:To prevent generation of transient noise at mode switching by providing a circuit holding an output DC voltage of a low frequency amplifier circuit to a value close to a reference voltage at the mode change of a tape recorder and eliminating/reducing the transient noise. CONSTITUTION:A voltage VM of a mode switching control signal inputted to a terminal 6b of a mode switching circuit 6 is higher than a control reference voltage VCR at the operating state of normal bias, transistors (TR) Q29, Q30 are operated, a current flows to a low frequency amplifier circuit 4 and a TRQ13 is operated. Thus, a bias current flows to the 1st stage of the circuit 4 from a reference voltage circuit 3 and an output DC voltage VD at a terminal 4e is set with a reference voltage of 1/2 power supply voltage VCC generated by the circuit 3. When the voltage VM at a terminal 6b is lower than the voltage VCR, the TRs Q29, Q30 are interrupted and TRs Q26, Q27 are conductive. Thus,TRs Q33-Q36 of transient noise elimination/reduction circuit 7 are conducted, a TRQ17 of the circuit 4 is cut off, the voltage VD is set to 1/2 VCC by the reference voltage and a DC voltage setting resistor R4, and since the fluctuation of the output DC voltage is less and no transient noise is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a low frequency amplifier capable of removing and reducing transient sounds generated when switching between recording and playback modes of a tape recorder.

(Prior Art) Fig. 1 is a circuit diagram showing a low frequency amplifier of a conventional tape recorder.In the figure, 1 is a power supply terminal to which power supply voltage Vcc is applied, 2 is a ground terminal, and 3 is a transistor Q+.
-Qs, a resistor R, and a resistor R7, from the output terminal 3a to the power supply voltage VI! A low impedance reference voltage circuit outputting a reference voltage of about H, 4, transistors Q, ~Q, 7. A low frequency amplifier circuit consisting of resistor R3 + DC voltage setting resistors R4 and R1, and equipped with internal input terminal 4m, external input terminal 4b + poor feedback terminal 4c, internal input terminal 4d, and external output terminal 4c, 5 is transistor Q
18~Q24. A constant current source circuit consisting of a resistor 6 and a resistor 1, 6 is a transistor Q□ to Q37. It is composed of a resistor 8 and a resistor 9, and has an internal output terminal 611. This is a mode switching circuit equipped with a mode switching control terminal 6b into which a mode switching control signal is input.

Next, the operation state and stop state due to mode switching will be explained in 9% of the operation of the circuit having the above configuration. First, the control reference voltage V at the node N of the mode switching' control terminal 6
at can be represented by the following formula (1).

VCn = Vee* (1) r@+r・ Note that r and r are resistance R8 and resistance R, respectively.
, Therefore, in the normal bias operating state, the control voltage VM of the mode switching control signal input to the mode switching control terminal 6b is higher than the control reference voltage Ver ((
VM:> V(!R). therefore.

Transistor Qyo and transistor Qso operate, and current flows. The current with is the internal output terminal 6m.

Flow through the low frequency amplifier circuit 40 input terminal 4d.

Transistors Q and s of the low frequency amplifier circuit 4 operate.

Due to the operation of this transistor Q1g), a bias current flows through the first stage of the low frequency amplifier circuit 4, and the output DC voltage Vn outputted from the output terminal 4e is set to approximately % of the power supply voltage Vcc. Next, when the mode switching button is set to a stopped state, the control voltage VM of the mode switching control signal input to the mode switching control terminal 6b is lower than the control reference voltage Vex ((vi
t (Ver). Therefore, transistor Q2° and transistor Q3° are cut off. For this reason,
Until now, transistor Qs.

The biased low frequency amplifier circuit 4 is stopped by the current mirror circuit of the transistor QCs. At this time, the output terminal 4e of this low frequency amplifier circuit 4
The output DC voltage VD output from the resistor R6 is expressed by the following equation (2) using the resistor R6, the resistor R6, and the transistor QI7.

Vo = VCC - Vaat Q17 (2) In this way, when the operation is stopped due to the mode switching operation, the output DC voltage VD output from the output terminal 4e of the low frequency amplifier circuit 4 varies from %Vec to approximately Vec. Since the change is large, a pre-transient occurs. Similarly, a pre-transient period also occurs when the mode switching operation is reversed.

However, in the conventional low frequency amplifier, the output DC voltage VD output from the low frequency amplifier circuit is approximately %Vcc in the normal bias operation state.

When the mode is switched, #1 becomes the power supply voltage Wee in the stopped state. For this reason, the output DC voltage fluctuates greatly, and a pre-transient period occurs. Further, when the device changes from a stopped state to an operating state, the output DC voltage similarly fluctuates greatly, and there is a drawback that a pre-transient occurs.

[Summary of the invention]

Therefore, an object of the present invention is to provide a low frequency amplifier that can eliminate and reduce the pre-transient when switching from an operating state to a stopped state or from a stopped state to an operating state due to mode/C switching. To achieve this purpose, Jin's invention always maintains the output DC voltage of the low frequency amplifier circuit at an output DC voltage close to the reference voltage when switching a desired mode, thereby eliminating and reducing the pre-transient voltage. It is equipped with a pre-transient removal/mitigation circuit, and will be explained below using an example.

[Embodiments of the invention]

FIG. 2 is a circuit diagram showing an embodiment of the low frequency amplifier according to the present invention. In the same figure, T is the transistor Qss
This is a pre-transient removal/mitigation circuit consisting of Q16.

Next, the operation of the circuit with the above configuration, particularly the operating state and stop state due to mode switching, will be explained. first,
In the normal bias operation state, the control voltage VM of the mode switching control signal input to the mode switching control terminal 6b is higher than the control reference voltage vcR (vm>vex). Therefore, transistor Q0 and transistor Q3° operate, and current flows. This current is applied to the internal output terminal 6a,
The signal flows through the input terminal 4d of the low frequency amplifier circuit 40, and the transistor QI3 of the low frequency amplifier circuit 4 operates. Due to the operation of the transistor Qll, a bias current flows through the first stage of the low frequency amplifier circuit 4, and the output DC voltage VD outputted from the output terminal 4e is set to about % of the power supply voltage Vec.

Next, due to mode switching, when the control voltage vM of the mode switching control signal input to the mode switching control terminal 6b is lower than the control reference voltage Ver (VM (Vex)), the transistors Q and Q3 are cut off. However, the transistor Qtn and the transistor Q2 become conductive.Therefore, the transistors Qss to Qsa of the pre-transient removal/mitigation circuit T become conductive.Therefore, the current mirror of the transistor Q+y of the low frequency amplifier circuit 4 becomes conductive. Transistors Qxs * QI * and Qs
The bias current of o is then cut off. For this reason, the transistor Ql? Is the transistor Ql of the low frequency amplifier circuit 4 not in the cut-off state? DC voltage setting resistors R4 and R6
Since the current flowing through the DC voltage setting resistors R3 and R4 is cut off, the voltage drop due to the DC voltage setting resistors R3 and R4 is eliminated. For this reason.

The output DC chamber EEvD of the output terminal 4e is approximately the power supply voltage Vc.
It is set to the reference voltage which is a of e. in this way.

Fluctuations in the output DC voltage are small and are virtually eliminated before the transient. Furthermore, when changing the mode from a stopped state to an operating state, there is similarly little variation in the output DC voltage, and transient noise can be substantially eliminated.

(Effects of the Invention) As described above in detail, the low frequency amplifier according to the present invention has the advantage of being able to eliminate and reduce transients during mode switching with a simple circuit configuration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional low frequency amplifier for a tape recorder, and FIG. 2 is a circuit diagram showing an embodiment of the low frequency amplifier according to the invention of Hitoshi Sha. 1...Power terminal, 2...Earth terminal. 3...Reference voltage circuit, 4...Low frequency amplifier circuit,
5...constant current source circuit, 6...mode switching circuit,
T: Pre-transient removal/mitigation circuit. QI-Qse...Transistor, R3~R,...
·resistance. In addition, in FIG. 1, the same reference numerals indicate the same or corresponding parts. Agent Masuo Oiwa Procedural Amendment (Voluntary) 1. Indication of the case: Japanese Patent Application No. 58-250244 2, Title of the invention: Low frequency amplifier 3, Person making the amendment 5, Subject of amendment (1) "Low frequency amplifier circuit" in the first line of page 4 of the specification is replaced with "Low frequency amplifier circuit"
"Low frequency amplification circuit". (2) In the 9th line of the same page, ``Because it changes,'' is corrected to ``Change.'' (3) Doodle “Before transition ~ occurs” in lines 9 to 11 on the same page.
Delete. (4) In line 12 of the same page of the same book, "however" is amended to "in this way." (Correct "QIIO" on page 6, line M20 of the 51st write down to rQmJ. (6) Add "due to the effect of the reference voltage and R4" after "rVp is" on page 7, line 6 of the same book. (7 ) Amend Figure 1 in the attached sheet.

Claims (1)

[Claims] A low-impedance reference voltage circuit that outputs a reference voltage of about H of the power supply voltage, a low-frequency amplifier circuit biased by this reference voltage circuit, and a low-frequency amplifier circuit that constantly maintains the output DC voltage of the low-frequency amplifier circuit when switching a desired mode. A low frequency amplifier characterized in that it is equipped with a transient sound removal/reduction circuit that maintains an output DC voltage close to the reference voltage and removes/reduces transient noise.