JPH04200138A - Transmission reception control circuit for cordless telephone set - Google Patents

Abstract

PURPOSE:To realize a natural talking state by selecting a compander circuit so that the compander circuit is used when the S/N is small and the compander circuit is not in use when the S/N is large. CONSTITUTION:A detection circuit 17 detects the S/N and selects a changeover device 19 to be thrown to the position of a terminal (b) only when it is detected that the S/N of both slave set and master set is a prescribed value or below thereby preventing a transmission reception signal from being inputted to a compander circuit 13. Thus, when the S/N is small, the compander circuit 13 compresses or expands the transmission reception signal to make talking while the S/N is improved and when the S/N is high, the transmission reception signal is processed without using the compander circuit 13, then natural talking state is ensured while eliminating a specific beat noise sound.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is an improvement of a transmitting/receiving circuit of a cordless telephone, particularly a transmitting/receiving control circuit that passes transmitted and received signals through a compander circuit as a noise reduction circuit in communication between a base unit and a slave unit. Regarding.

[Prior Art] In general, a cordless telephone uses a compander circuit for the purpose of reducing noise when transmitting and receiving audio signals between a pace set as a base unit and a handset as a slave unit.

FIG. 4 shows the internal circuits of a handset and a base unit in a cordless telephone, and in the handset shown in FIG. And the transmitting circuit 12 is connected to the compander circuit 13.

A speaker 15 is connected to the compander circuit 13 via a speaker amplifier 14a, and the speaker 15 outputs the audio received by the slave device.

A microphone 16 is connected to the compander circuit 13 via a microphone amplifier 14b, and the audio input from the microphone 16 is compressed by the compander circuit 13 and then output to the transmitting circuit 12. The audio signal is modulated by an FM (frequency modulation) method or the like and output from the antenna 10.

On the other hand, also in the base device shown in FIG.
1 and the transmitting circuit 22 via the compander circuit 23.
A line-to-four line conversion circuit 24 is connected. This 2 lines-4
The line conversion circuit 24 is connected to the telephone line, and performs conversion processing of the transmitted and received signals between the telephone line and the cordless telephone, as well as adjusting the level of the voice signal.The voice signal transmitted from the telephone line is converted to a compander. After being compressed by the circuit 23, it is supplied to the transmitting circuit 22, and this transmitting circuit 22
Similarly, an audio signal modulated by the FM method or the like is output from the antenna 20.

In addition, the receiving circuit 11.21 of the handset and base unit demodulates the signal received by the antenna 10.20 and outputs it to the compander circuit 13.23.
At 3.23, the signal is expanded and returned to the original signal.

FIG. 5 shows the internal configuration of the compander circuit 13.23, and the compander circuit 13.23 is a compressor (
The transmitter is composed of a compressor A and an expander B, with the compressor A compressing the transmitted signal and the expander B expanding the received signal. That is, the compressor A consists of a variable gain amplifier circuit a, a rectifier circuit and a smoothing capacitor C, and compresses the audio range by amplifying a weak audio signal. Further, the expander B is composed of a variable gain amplifier circuit d, a rectifier circuit e, and a smoothing circuit f, and performs an expansion operation opposite to that of the compressor, and operates so that the loss increases as the audio level decreases. Therefore, the sixth
As shown in the figure, the audio signal to be transmitted is modulated in a compressed state, transmitted as a radio frequency (RF) band signal, and upon reception, it is demodulated and then expanded to its original level. This makes it possible to reduce noise generated in audio signals during transmission, etc., while expanding the dynamic range.

[Problem to be solved by the invention, M] However, in the transmission/reception control circuit of a conventional cordless telephone, the compander circuit 13.23 is configured to control the gain after rectifying and smoothing the signal. Phenomena occur such as a delay in the rise of control in response to an input signal that changes rapidly, and a noise level changing depending on the level of the input signal. As a result, although the signal-to-noise ratio (SN ratio) is improved, there is a problem in that a subtle and unique sound is generated during a call, creating an unnatural feeling.

In particular, in wireless calls between the slave unit and the base unit, even if there is no need to reduce noise under conditions where the S/N ratio is good,
Since the compander circuits 13 and 23 are always operating, an unnatural feeling always remains during a call.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a transmission/reception control circuit for a cordless telephone that can selectively use a compander circuit for noise reduction and reduce unnaturalness as much as possible. It's about doing.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a base unit connected to a telephone line and a slave unit that communicates wirelessly with the base unit, In the transmitting/receiving control circuit of a cordless telephone with a built-in compander circuit in the handset, there is a detection circuit that detects the signal-to-noise ratio of the signal obtained by the receiving circuit, and the output of this detection circuit is transmitted between the base unit and the handset. In addition to controlling transmission and reception between the The present invention is characterized by being provided with a switch for switching to.

[Operation] According to the above configuration, the signal-to-noise ratio (SN ratio) is detected by the detection circuit, for example, by detecting a noise component outside the audible band or by estimating it from the electric field strength. When the SN ratio is smaller than a predetermined value, the signal is compressed and expanded by the Hunpanda circuit.

On the other hand, when the SN ratio is large, the compander circuit is not used by the switch, and the audio signal is transmitted and received in a normal state, resulting in high-fidelity audio.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of a handset and a base unit of a cordless telephone according to an embodiment, and the same members as in the conventional configuration are given the same numbers and their explanations will be omitted.

The slave device in FIG. 1A includes a detection circuit 17 connected to the reception circuit 11 that detects a signal-to-noise ratio (SN ratio), a control section 18 that inputs the output of the detection circuit 17, and a control section 18 that inputs the output of the detection circuit 17. Switches 19a and 19b are provided which are switched and controlled by the section 18, and the switch 19a switches whether or not the output from the receiving circuit 1 is expanded by the compander circuit 13, while the switch 19b switches whether or not to compress the output of the microphone amplifier 14b by the compander circuit 13.

The base unit in FIG. 2B includes an SN ratio detection circuit 27 connected to the reception circuit 21, a control section 28 that inputs the output of this detection circuit 27, and a switching device controlled by the control section 28. 29a and 29b are provided, and the switching device 2
9a switches whether or not to expand the output of the receiving circuit 21 with the compander circuit 23, and one switch 29b switches whether or not to compress the output of the 2-wire to 4-wire conversion circuit 24 with the compander circuit 23. I do.

FIG. 2 shows two configurations of the detection circuit 17 (27), and FIG. 2A shows a circuit that detects the SN ratio using noise components outside the audible band. For example, a band pass filter (BPF) 31 that passes a signal of 10 kllz, a rectifier circuit 32, and a comparator 33 that determines whether the noise level is greater than a predetermined value.
It consists of Therefore, this detection circuit 17 (27)
According to
The signal of z is extracted, and the SN ratio can be determined based on this noise component. , for example, outputs a signal at the old GH level.

On the other hand, the circuit in figure (b) has an SN of
The comparator 34 compares the electric field strength value output from the receiving circuit with a predetermined value, and when the value is larger than the predetermined value, for example, when the distance is close, the comparator 34 detects the Output a signal.

The embodiment has the above configuration, and its operation will be explained below based on FIG. 3.

First, in step 100 of FIG. 3, the detection circuit 17 (27
), the SN ratio is detected, and the process moves to the next step 101.

In step 101, it is determined whether the detected value of the SN ratio has become below a predetermined value. If "NO" (when the SN ratio is small), the process returns to step 100; if "YES", that is, the SN ratio When a signal of the old gh level indicating that From (22), a switching control signal is transmitted to the other party.

In the next step 103, it is determined whether or not a switching control has been received from the other party. If "No", the process returns to step 100; if "YES", step 104 is performed.
The controller 18 (28) switches the switch 19a,
19b (29a, 29b) to the terminal side. That is, in the embodiment, the switch 19 (29) is switched to the terminal side and the transmitted/received signal is sent to the compander circuit 13 only when it is determined that the SN ratio of both the slave unit and the base unit is below a predetermined value. Avoid entering it.

Therefore, when the SN ratio is small, the compander circuit 1B (2
In B), the transmitted and received signals are compressed or expanded, and a call is made with an improved S/N ratio. However, when the S/N ratio is large, the transmitted and received signals are processed without using the compander circuit 13 (23), so this is a unique feature. It is possible to maintain a natural conversation state without the buzzing sound.

Although the operation shown in FIG. 3 is performed at predetermined time intervals in the embodiment, it can also be performed under predetermined conditions such as when the handset starts to be used or when it is moved.

In the above embodiment, the compander circuits 13 and 23 are switched when both the slave unit and the base unit detect that the S/N ratio is large, but the compander circuits 13 and 23 are switched only when one side detects it. Alternatively, a detection circuit may be provided only on one side to perform switching control.

[Effect of the invention] As explained above, the detection circuit for detecting the SN ratio, the SN
When the ratio is small, a compander circuit is used, and when the SN ratio is large, the compander circuit is not used.
Since the compander circuit was made to operate selectively,
When the SN ratio is small, noise is effectively reduced, and when the SN ratio is large, it is possible to prevent deterioration in sound quality caused by the compander circuit and realize a natural conversation state.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a transmission/reception control circuit of a cordless telephone according to an embodiment of the present invention.
a) is a diagram showing the slave device, (b) is a diagram showing the master device, FIG. 2 is a program diagram showing the configuration of the detection circuit of the embodiment, FIG. 3 is a flowchart showing the operation of the embodiment, and FIG. 4 is a diagram showing the operation of the embodiment. 5 is a block diagram showing the configuration of a transmission/reception control circuit of a conventional cordless telephone, in which FIG. 5A shows a handset, FIG. FIG. 6 is an explanatory diagram showing the operation of the compander circuit. 11.21 ... Receiving circuit 12.22 ... Transmitting circuit 13.23 ... Compander circuit 17.27
...Detection circuits 18, 28...Control units 19a, 19b, 29a, 29b -Switcher A...
・Compressor B...Expander

Claims (1)

[Claims] Transmission/reception of a cordless telephone comprising a base unit connected to a telephone line and a slave unit that communicates wirelessly with the base unit, the base unit and the slave unit having a built-in compander circuit. The circuit includes a detection circuit that detects the signal-to-noise ratio of the signal obtained by the receiving circuit, and a detection circuit that controls transmission and reception of the output of this detection circuit between the base unit and the slave unit. A cordless telephone characterized in that it is provided with a switch that passes the transmitted and received signals through the compander circuit when the detected signal-to-noise ratio is small, and switches the transmitted and received signals not to pass through the compander circuit when the detected signal-to-noise ratio is large. Transmission/reception control circuit.