JPS6393248A - Receiving amplifier - Google Patents

Abstract

PURPOSE:To improve the speaking quality such as distinction by providing a preceding-stage amplifier having a variable frequency characteristic in the preceding stage of an output circuit. CONSTITUTION:A preceding-stage amplifier 7 consists of a bias circuit 4, an operational amplifier 6, resistances R1, R2, and R3, capacitors C1, C2, and C3, and a switch SW. The sound signal supplied to a reception input terminal IN is amplified by the preceding-stage amplifier 7 and is furthermore amplified by an output circuit 1 and is supplied to a receiver 3. In this case, a proper capacitor C is selected by the switch SW to obtain a desired reception tone quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a receiving amplifier suitable for use in a telephone set.

[Prior Art] The frequency characteristics of a receiving system consisting of a receiving amplifier and a handset of a conventional telephone set are set to be almost flat in a certain same wave number band, and the characteristics are fixed.

[Problems to be solved] With such telephones, if the communication system between the caller and the called party suffers from deterioration of frequency characteristics or noise, it is difficult to make a call while the quality of the received call remains degraded. I have no choice but to. Furthermore, since there are individual differences in human hearing, clarity may decrease if the frequency characteristics cannot be changed.

[Means for Solving Problems] The present invention has been made in view of the above circumstances, and amplifies the audio signal input to the receiver input terminal.

A receiver amplifier having an output circuit that outputs an output is characterized in that a pre-stage amplifier is provided in a pre-stage of the output circuit, and the pre-stage amplifier has variable frequency characteristics.

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

:tSi diagram is a block diagram showing a receiving amplifier according to an embodiment of the present invention. In this figure, line terminal Ll
, L2, an output circuit 1 and a power supply 2 are inserted in series, and the output circuit 1 amplifies the signal supplied to its input terminal 1a, outputs it from the output terminal 1b, and supplies it to the receiver 3. do.

Further, a bias circuit 4 and a constant current source 5 are inserted in series between the line terminals Ll and L2 in parallel with the output circuit 1 and the power supply 2, and the output terminal of the bias circuit 4 is connected to a calculation terminal. It is connected to the non-inverting input terminal of amplifier 6. The bias circuit 4 then supplies a constant bias voltage to the non-inverting input terminal of the operational amplifier 6. On the other hand, the inverting input terminal of the operational amplifier 6 is connected to the receiving input terminal IN via a resistor R1. Further, resistors R2 and R3 are inserted in series between the inverting input terminal and the output terminal of the operational amplifier 6, and capacitors C+ and C2 are connected to the connection point between these resistors R2 and R3.
, C:l (C3<CI<C2) are commonly connected. In this case, these capacitors C1, C2,
The other end of C3 is open and selectively connected to the inverting input end of operational amplifier 6 by switch SW.

Further, the output terminal of the operational amplifier 6 is connected to the input terminal 1a of the output circuit I, and the operational amplifier 6 is connected to the receiving input terminal I.
The audio signal supplied to N is amplified and supplied to output circuit 1. In this case, the gain A of the operational amplifier 6 is, for example, R when the capacitor CI is selected as shown in the figure.

It is expressed as follows. As you can see, the gain of the operational amplifier 6 is inversely proportional to the frequency, so if you connect capacitor C2 with a larger capacitance than capacitor C1, the high frequency level of the received signal will decrease. When the capacitor is connected or not connected, the level of the high frequency is higher than the height of the capacitor CI.

In addition, the bias circuit 4, the operational amplifier 6, the resistor R+,
A pre-stage amplifier 7 is constituted by R2, R3, capacitors CI, C2, C3, and switch SW.

In the above configuration, the audio signal supplied to the receiver input terminal IN is amplified by the preamplifier 7, and further output circuit l.
The signal is amplified by and supplied to the receiver 3. in this case,
By selecting an appropriate capacitor C using the switch SW, a desired reception sound quality can be obtained as shown in FIG.

In addition, I adjusted the sound quality by using a capacitor in the return section. In this case, it is also possible to use an inductance instead of the resistor R1 to make the feedback resistor a pure resistor.

[Effects of the Invention] As explained above, according to the present invention, in a receiver amplifier having an output circuit that amplifies and outputs an audio signal input to a receiver input terminal, a preamplifier is provided at a stage before the output circuit. Since the frequency a characteristic of the preamplifier is made variable, it is possible to suppress or correct low noise and deterioration of frequency characteristics in the communication system between one caller, and also to compensate for individual differences in human hearing. Since it becomes possible to support communication, it is possible to improve call quality such as clarity.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a receiving amplifier according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing changes in frequency characteristics. 1: Output circuit la: Input end 1b: Output end 2: Power supply

Claims (1)

[Claims] In a receiving amplifier having an output circuit for amplifying and outputting an audio signal input to a receiving input terminal, a pre-stage amplifier is provided at a stage preceding the output circuit, and the pre-stage amplifier has variable frequency characteristics. Characteristic receiver amplifier.