JP2001230647A - Expander circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an expander circuit for reducing a noise at no input time of audio or the like. SOLUTION: In the expander circuit for expanding the level of an output signal corresponding to the level of an input signal, this circuit is provided with a level detector 2 for detecting the level of the input signal, a first multiplication circuit 3 for multiplying the output of the level detector 2 to the input signal as a multiplying signal, an expander output control circuit 4 for outputting an expander output control signal for attenuating the output signal, when the level of the multiplying signal from the level detector 2 is compared with a prescribed comparative value and is equal to or lower than the comparison value, and a second multiplier 8 for multiplying the output of the first multiplication circuit 3 and the expander output control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an expander circuit of a compander used for a radio telephone device such as a portable telephone.

[0002]

2. Description of the Related Art In a wireless telephone device such as a cellular phone, when an audio signal is FM-modulated and transmitted to a wireless line, in order to prevent signal-to-noise (S / N ratio) deterioration in the wireless line, You are using a compander. The compander is a general term for two circuits, an expander circuit and a compressor circuit. The expander circuit is a circuit that adjusts the signal level of audio or the like to extend the output signal level with respect to the input level, and the compressor circuit is the circuit that adjusts the signal level of audio or the like to compress the output signal level with respect to the input level. .

The compressor circuit sets a signal level, for example, -20 dBv, as a reference level for a signal such as voice, amplifies a signal lower than the reference level so as to approach the reference level, and amplifies a signal higher than the reference level to a reference level. Attenuate to approach. A signal modulated by FM modulation or the like using the signal processed by the compressor circuit is output to a wireless line. By performing this processing, it is possible to prevent signal-to-noise degradation of a low-level signal in a wireless channel.

A demodulator uses an expander circuit to restore a demodulated signal to an original signal. Predetermined signal level,
For example, a reference level of -20 dBv is set, and a signal smaller than the reference level is attenuated so as to be a signal before the compressor circuit input, and a signal larger than the reference level is amplified so as to approach the signal level before the compressor circuit input.
An expander input signal having the same level as the reference level is output from the expander circuit at the same signal level.

[0005] An expander circuit is used to return the signal compressed by the compressor circuit to a signal level before passing through the compressor circuit again. The compression / expansion ratio of the input signal to the output signal with respect to the reference level of the compressor circuit and the expander circuit is 2: 1 for compression and 1: 2 for expansion, and the signal of a signal such as audio is passed through the compressor circuit and the expander circuit. The signal ratio after passing the previous signal is 1: 1.

FIG. 5 is a diagram showing a circuit configuration for explaining a conventional expander circuit.

In the expander circuit shown in FIG. 5, 2 is a level detector, 3 is a multiplier, 21 is a rectifier (A
BS), 22 is a low-pass filter (LPF), and 23 is an amplifier (AMP). The amplifier 3 may be constituted by a variable amplifier or the like. Here, a configuration suitable for digital signal processing is shown as an example.

[0008] The expander input signal Ye (n) is
, Multiplies the output Xe (n) from the level detector 2 to output an expander output signal Ze (n). Level detector 2
The rectifier 21 performs full-wave rectification on the expander input signal Ye (n) and outputs the signal to the low-pass filter 22. The low-pass filter 22 removes a high-frequency component of the rectified signal voltage of the rectifier 21 and outputs a DC component (LPF-OUT) to the amplifier 23. The amplifier 23 amplifies the DC component from the low-pass filter 22 and outputs a multiplication signal Xe (n) for multiplication by the multiplier 3.
The multiplier 3 converts the expander input signal Ye (n) into a multiplied signal X
Output Ze (n) as a result of multiplication by e (n) (Ze (n) = Ye (n)
* Xe (n)).

Here, a level where Ze (n) = Ye (n) is set as an expander reference level. Here, the expander reference level is -20 dBv. Here, if the input level range of the expander circuit is based on the US mobile phone standard,
The reference level is +10.6 dB to −21.02 dB. The expander circuit expands and outputs the signal level according to the level of the expander input signal, so that the noise sent from the transmitter is faithfully expanded and heard as background noise when no voice is input. There is a disadvantage that it deteriorates.

Also, the demodulation noise generated in the demodulator itself and the noise added in the radio line are expanded by the expander circuit to reduce the noise component, but since the expander expansion ratio is 1: 2, it is expanded. It was difficult to reduce the level below the ratio.

The conventional expander circuit expands the noise added to the radio signal input to the demodulator and the noise generated by the demodulator at a ratio of 1: 2 based on the expander reference level. There is a problem that unnecessary noises other than the signal transmitted from the device are also restored.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a conventional expander circuit in which the expansion ratio at a low level is changed to increase the level signal expansion ratio, and when the signal is restored by the expander circuit of the demodulator. It is an object of the present invention to further reduce the low-level noise component and reduce the noise component demodulated when there is no voice signal or the like, thereby improving the communication quality of a wireless telephone device such as a mobile phone.

In order to achieve such an object, a first expander circuit of the present invention multiplies an output of the level detector by detecting a level of an input signal input to the expander circuit. A first multiplying circuit that multiplies the input signal as a signal; and a level of the multiplied signal of the level detector that is compared with a predetermined comparison value to attenuate an output signal of the expander circuit when the level is equal to or less than the comparison value. Output adjustment circuit that outputs an expander output adjustment signal for the second multiplication circuit, and a second multiplier that multiplies the output of the first multiplication circuit by the expander output adjustment signal. The output from the vessel is output as an output signal.

According to a second aspect of the present invention, there is provided the expander circuit according to the first aspect of the present invention, further comprising the expander output adjustment signal provided between the expander output adjustment circuit and the second multiplier. A squaring circuit for squaring and outputting is provided.

Further, as an analog circuit therefor, in an expander circuit for extending the level of the output signal with respect to the level of the input signal, a level detector for detecting the level of the input signal and an output level from the level detector are provided. A first voltage-controlled amplifier for amplifying an input signal; and a limiter for receiving an output from the level detector and limiting the output level to be equal to or less than a predetermined value. An expander output adjustment circuit that outputs an expander output adjustment signal of a level limited by the following, and a second voltage control amplifier that amplifies the output of the first voltage control amplifier in accordance with the expander output adjustment signal. The output from the second voltage controlled amplifier is output as an output signal.

[0016]

Therefore, by using the expander circuit of the present invention and inputting the signal obtained by demodulating the modulated signal from the transmitter by the demodulator to the expander circuit of the present invention, the background noise on the transmission side when no sound is input is obtained. Can be lower than the noise level at the transmitter input.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the expander circuit of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram for explaining a first embodiment of the expander circuit. In the circuit shown in the figure, the same circuit components as those of the conventional example are denoted by the same reference numerals.

As shown in FIG. 1, 2 is a level detector, 3 is a first multiplier, 4 is an expander output adjustment circuit, and 8 is a second multiplier. The level detector 2 includes a rectifier 21, a low-pass filter 22, and an amplifier 23. The expander output adjustment circuit 4 includes a multiplier 41 and a level comparison circuit 42. Here, the multipliers 3 and 8 may be constituted by variable amplifiers or the like. Here, a configuration suitable for digital signal processing is shown.

Next, the operation of the present invention will be described. The expander input signal Ye (n) is connected to the multiplier 3 and the level detector 2. In the level detector 2, the expander input signal Ye (n) is full-wave rectified by the rectifier 21 and output to the low-pass filter 22. The low-pass filter 22 removes the high-frequency component of the rectified signal voltage of the rectifier 21 and removes the DC component (L
PF_OUT) to the amplifier 23. The amplifier 23 amplifies the DC component from the low-pass filter 22 and outputs a multiplication signal Xe (n) for multiplication by the multiplier 3. The multiplier 3 outputs Ze (n) as a result of multiplying the expander input signal Ye (n) by the multiplication signal Xe (n) (Ze (n) = Ye (n) * Xe (n)).

Here, the level where Ze (n) = Ye (n) is set as the expander reference level. Therefore, the reference level of the expander circuit can be changed by changing the amplification factor of the amplifier 23 of the level detector 2. The output Ze (n) of the multiplier 3 is input to a multiplier 8 for changing the expansion ratio of the expander circuit. The expander output adjusting circuit 4 has a multiplied signal Xe (n) output from the level detector 2.
Is input to the multiplier 41 as an input signal. Multiplier 41
Then, a level comparison coefficient Ke (n) is obtained by multiplying by a coefficient paraC for setting a change point for changing the operation of the expander expansion ratio 1: 2 at a low level (Ke (n) = Xe (n) * paraC). .

The level comparison coefficient Ke (n) is calculated by the level comparator 42
And is compared with a predetermined level comparison value ref. When the level comparison coefficient Ke (n) is greater than or equal to the level comparison value ref, the level comparator 42 outputs the level comparison coefficient Ke (n).
Is set to 1.0 and input to the multiplier 8. Level comparison coefficient
If Ke (n) is smaller than the level comparison value ref, the level comparison coefficient Ke (n) is directly input to the multiplier 8 (Ke (n) ≧ 1.
0 then Ke (n) = 1.0).

In the multiplier 8, the output Ze (n) from the multiplier 3 is output.
Is multiplied by a level comparison coefficient Ke (n) output from the level comparator 42 of the expander output adjustment circuit 4 to obtain an expander output signal Zeo (n) (Zeo (n) = Ze (n) * Ke ( n)).

In order to numerically indicate the operation result for the expander input signal Ye (n), the expander reference level is set to -2.
0 dBv. Also, if the input level range of the expander circuit is set to the US mobile phone standard as an example, the reference level
+10.6 dB to −21.02 dB.

Reference input of expander input signal Ye (n)
Assuming that 20 dBv is 1.0 and the expansion ratio at a level of about 20 dB or less from the reference level is changed, paraC is 10.0.
The operation can be changed by setting to.

If the expander input level Ye (n) is lower than the reference level by −20 dB, Ye (n) = 10 ^(−20/20) =
0.1, multiplied signal: Xe (n) = 0.1,
Multiplier 3 output: Ze (n) = Ye (n) * Xe (n) = 0.0
1. Level comparison coefficient: Ke (n) = Xe (n) * paraC = 0.
1 * 10.0 = 1.0, expander output: Zeo (n)
= Ze (n) * Ke (n) = 0.01 * 1.0 = 0.01.

Therefore, Zco (n) = 20 log10 (0.0
1) =-40.0 dB Up to this level, the expansion ratio of the expander circuit is 1: 2. Below this level, the expansion ratio increases.

On the other hand, for example, when the expander input level Ye (n) is lower than the reference level by −22 dB, Ye (n) = 1
0 ^(-22/20) = 0.08, division signal: Xe (n) = 0.
08, multiplier 3 output: Ze (n) = 0.0064, level comparison coefficient: Ke (n) = Xe (n) * paraC = 0.08 * 1
0.0 = 0.8, expander output: Zeo (n) = Ze (n)
* Ke (n) = 0.0064 * 0.8 = 0.0051
It becomes 2.

Therefore, Zeo (n) = 20 log10 (0.00
512) = − 45.81 dB, which is −1.94 dB smaller than that of a normal expander circuit.

FIG. 2 is a block diagram showing an expander circuit for explaining a second embodiment of the present invention. In the circuit in the figure, the same circuit parts as in the first embodiment are given the same numbers.

The expander circuit of the second embodiment is similar to the expander circuit of the first embodiment.
Squarer circuit 6 after the expander output adjustment circuit 4
Is added. Since the description of the operation is the same as that of the first embodiment up to the expander output adjustment circuit 4, reference is made to the first embodiment. Here, the operation after the expander output adjustment circuit 4 will be described. The level comparison coefficient Ke (n) from the expander output adjustment circuit 4 is Ke (n) ≧ 1.0 then Ke (n)
= 1.0, and this level comparison coefficient Ke (n) is input to the squaring circuit 6. The squared level comparison coefficient Ke (n) is Ke
When (n) <1.0, the coefficient is further reduced because it is squared, and the expansion ratio at a lower level than in the first embodiment is further increased. When this is compared with the first embodiment at a level where the expander input signal Ye (n) is −22 dB lower than the reference level, the result is as follows.

When the expander input signal Ye (n) is -22 dB lower than the reference level, the operation is as follows: Ye (n) = 10
^(-22/20) = 0.08, division signal: Xe (n) = 0.
8, divider output: Ze (n) = 0.0064, level comparison coefficient: Ke (n) = Xe (n) * paraC = 0.08 * 1
0.0 = 0.8, expander output: Zeo (n) = Ze (n)
* Ke (n) ² = 0.0064 * 0.64 = 0.004
096.

Therefore, Zeo (n) = 20 log10 (0.00
4096) =-47.75 dB, and an attenuation value of -3.88 dB than that of a normal expander circuit and twice as large as that of the first embodiment can be obtained.

FIG. 3 is a diagram in which the first embodiment of the expander circuit is constituted by an analog circuit. The circuit shown in FIG.
Circuit portions that are the same as those in the first embodiment are given the same numbers.

As shown in FIG. 3, 2 is a level detector, 10 and 11 are voltage control amplifiers, 4 is an expander output adjustment circuit, and the level detector 2 is a rectifier 21;
A low-pass filter 22 and an amplifier 23 are included. The expander output adjustment circuit 4 may include an amplifier 411 and a limiter 412, and the amplifier 411 may include a variable amplifier or the like.

FIG. 4A shows the operation of the voltage controlled amplifiers 10 and 11 with respect to the control voltage. Since the operation of the level detector 2 is the same as that of the first embodiment, the description of the operation is omitted here, but FIG. 4B shows the input / output characteristics of the level detector, and FIG. 2 shows the overall characteristics of the control amplifier 11.
This characteristic is the same as that of the conventional compander.

Next, the operation of the expander output adjusting circuit 4 will be described. As shown in FIG. 3, in the expander output adjustment circuit 4, the output Xe (n) of the level detector 2 is input to the amplifier 411 as an input signal to change the operation of the expander expansion ratio at a low level. The signal is amplified to obtain an output for setting a point, and output to the limiter 412. The limiter 412 outputs the output Ke (n) to the voltage control amplifier 11 as a result of limiting the output of the amplifier 411 to a level at which the amplification degree of the voltage control amplifier 11 becomes 1 or more.
In the voltage controlled amplifier 11, the output Ze of the voltage controlled amplifier 10
(n) is controlled by the limiter output Ke (n) to control the amplification degree, thereby obtaining the expander output Zeo (n).

FIGS. 4D to 4F show this operation, and FIG. 4D shows the input / output characteristics of the amplifier 411. In FIG. 4D, the level detector output Xe (n) is multiplied by 10 and output to the limiter 412. FIG. 4E shows the limiter 41.
FIG. 6 is a diagram showing the operation of No. 2 in which the input voltage is limited and output. Here, it is set so that a voltage of 1 V or more is not output. FIG. 4F shows the overall operation characteristics of the expander output adjustment circuit 4 and the voltage control amplifier 11,
The output Ze (n) is input to the voltage controlled amplifier 11 whose amplification is controlled by the limiter output Ke (n), and the expander output signal Zeo
(n).

In this figure, the voltage is controlled so that the voltage of Ze (n) of 0.01 V or less is attenuated.

As described above, according to the present invention, the expansion ratio of the low-level expander input signal can be made larger than that in the first embodiment. Ambient noise and the like can be made even lower than the expander circuit of the first embodiment of the present invention, so that the communication quality is improved.

FIG. 6 is a diagram for explaining the input / output characteristics of the expander circuit of the present invention. The horizontal axis is the expander input signal level, and the vertical axis is the expander output signal level, both 20log10 (Ye (n)) and 20log10 (Ze
o (n)).

As shown in FIG. 6, since the expansion ratio of the low-level expander input signal can be increased,
The low-level ambient noise when no sound is input by the compressor circuit on the transmitting side can be reduced to a level lower than the level when the conventional expander is output, reducing noise during no sound and improving call quality. improves.

That is, the expander circuit of the present invention operates at a stretch ratio of 1: 2 at a level required for communication, and can increase the expand ratio of the expander circuit at a low-level signal such as unvoiced sound. Since the signal can be output from the expander circuit at a level smaller than the signal level input on the transmitter side, background noise when no sound is input on the transmission side can be reduced.

[0043]

As described above in detail, according to the expander circuit of the present invention, the expansion ratio at the low level is made larger than the expansion ratio at the high level. When restored, the low-level noise component is further reduced, and the noise component demodulated when there is no audio signal or the like is reduced, so that the communication quality of a wireless telephone device such as a mobile phone can be improved.

According to the second expander circuit of the present invention, the first expander circuit of the present invention further includes the expander output adjustment signal between the expander output adjustment circuit and the second multiplier. Since the squaring circuit for squaring and outputting is provided, the expansion ratio at a lower level can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an expander circuit according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an expander circuit according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of an expander circuit according to a third embodiment in which the expander circuit according to the first embodiment is configured by an analog circuit.

FIG. 4 is a diagram for explaining operation characteristics of each functional block of the expander circuit according to the third embodiment.

FIG. 5 is a configuration diagram for explaining a conventional expander circuit.

FIG. 6 is a diagram illustrating input / output characteristics of an expander circuit.

[Explanation of symbols]

2 ... Level detector, 3 ... Multiplier, 4 ... Expander output adjustment circuit, 6 ... Squaring circuit, 8 ... Multiplier, 10, 11 ... Voltage control amplifier, 21 ... Rectifier, 22 ... Low pass filter, 23,411 ... Amplifier, 412 ... limiter

Claims (3)

[Claims] 1. An expander circuit for extending a level of an output signal with respect to a level of an input signal, a level detector for detecting a level of the input signal, and multiplying the input signal by using an output of the level detector as a multiplication signal. A first multiplying circuit that outputs an expander output adjustment signal for comparing the level of the multiplied signal of the level detector with a predetermined comparison value and attenuating the output signal when the level is equal to or less than the comparison value. An expander output adjustment circuit; and a second multiplier for multiplying the output of the first multiplication circuit by the expander output adjustment signal, wherein an output from the second multiplier is used as the output signal. An expander circuit characterized by outputting. 2. The expander circuit according to claim 1, further comprising: said expander output adjusting circuit and said second expander circuit.
A squaring circuit for squaring and outputting the expander output adjustment signal between the multiplier and the multiplier. 3. An expander circuit for extending a level of an output signal with respect to a level of an input signal, comprising: a level detector for detecting a level of the input signal; A first voltage control amplifier for amplification; and a limiter for receiving an output from the level detector and limiting the output level to be equal to or less than a predetermined value, wherein the limiter is used to attenuate the output signal. An expander output adjustment circuit that outputs an expanded output adjustment signal of a given level, and a second voltage control amplifier that amplifies the output of the first voltage control amplifier in accordance with the expander output adjustment signal. And an output from the second voltage controlled amplifier as the output signal.