Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
1998-11-23
2001-05-22
Vo, Nguyen T. (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S303000, C455S306000
Reexamination Certificate
active
06236846
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a wireless receiver and, more particularly, relates to a wireless receiver for improving intelligibility of reception signals and a reception method therefor.
A tone quality switching function of a speaker in a wireless receiver, for example, is one of conventional means for improving intelligibility of reception signals in the wireless receiver.
FIG. 1
of the accompanying drawings is a block diagram showing a structural example of a wireless receiver according to the prior art. This drawing shows in detail the construction of a speech power amplification circuit equipped with a speaker tone quality switching function.
As shown in
FIG. 1
, the wireless receiver includes a reception unit having an antenna
50
, a front end portion
51
, a first intermediate frequency portion
52
, a second intermediate frequency portion
53
, a detection circuit
54
and a speech signal processing circuit
55
, a speech power amplification circuit
20
coupled to the reception unit and a speaker
2
for reproducing the speech signal form the speech power amplification circuit
20
.
The radio wave transmitted from the not-shown partner side wireless transmitter is received by the front end portion
51
through the antenna
50
as the wireless frequency signal (high-frequency signal). The wireless frequency signal received by the front end portion
51
is down-converted to the first intermediate frequency signal by the first intermediate frequency portion
52
, and then further down-converted to the second intermediate frequency signal by the second intermediate frequency portion
53
.
The output signal from the second intermediate frequency portion
53
is demodulated by the detection circuit
54
and supplied to the speech signal processing circuit
55
.
The speech signal processing circuit
55
limits the frequency band of the demodulated signal from the detection circuit
54
to the speech band and amplifies with a predetermined gain thereby to output as a base band signal (speech band signal) to the speech power amplification circuit
20
. The speech power amplification circuit
20
includes a tone quality control unit
22
for controlling tone quality of a base band signal from the speech signal processing circuit
55
and a speech power amplifier
14
for amplifying the speech signal controlled by the tone quality control unit
22
. The tone quality control unit
22
includes a switch
13
, a central processing unit (CPU)
7
such as a microcomputer, a resistor
9
, capacitors
10
and
11
and an analog switch
12
.
The speech band signal outputted from the speech signal processing circuit
55
is amplified by the speech power amplifier
14
and is outputted as a reception speech from the speaker
2
. The analog switch
12
is controlled to an ON state when the control input from the central processing unit
7
is at an “H” (high level) and to an OFF state when the control input is at an “L” (low level), for example.
The circuit including this speech power amplifier
14
forms a high-pass filter (HPF). Because the analog switch
12
is an ON state at the normal time, the cut-off frequency of the HPF is determined by the following equation (1):
fc
=½{2
&pgr;R
(
C
1
+C
2
)} (1)
Here, R is a resistance value of the resistor
9
and C
1
and C
2
are the capacitance values of the capacitors
10
and
11
, respectively.
When the switch
13
is turned ON, the tone quality switching function is made ON (effective) and the central processing unit
7
outputs a control signal of the “L”. Therefore, the analog switch
12
is turned OFF and the cut-off frequency of the HPF is determined by the following equation (2):
fc
=½
&pgr;RC
(2)
Therefore, the cut-off frequency becomes high when the tone quality switching function is turned ON or made effective.
FIG. 2
shows a gain-v-frequency characteristic curve at this time.
FIG. 3
shows an NQ (Noise Quieting) curve of the wireless receiver by using a saturation value of an S (Signal) curve (at the time of reception of a 1 kHz standard modulated wave) as a reference level. The frequency characteristics at the time of tone quality switching function ON will be compared with the frequency characteristics at the normal time (tone quality switching function OFF) with reference to the characteristic example shown in FIG.
3
. It can be appreciated that the noise output level decreases at a reception input field intensity of about −130 dBm or below at the time of tone quality switching function ON in comparison with the normal time.
In the practical operation of the wireless receiver, however, weak field signals below about −130 dBm are those which are hardly intelligible, and no practical improvement can be attained in intelligibility even when the noise output level is reduced to some extents by turning ON the conventional tone quality switching function.
On the other hand, the reception input field intensity, at which the noise output level increases and intelligibility starts deteriorating drastically is around about −120 dBm on the NQ curve shown in
FIG. 3
(at the normal time). Referring to
FIG. 3
, a remarkable decrease of the noise output level cannot be observed in this area near about −120 dBm even when the tone quality switching function is turned ON. Therefore, even when a user of the conventional wireless receiver recognizes deterioration of intelligibility and turns ON the tone quality switching function during the practical operation, a substantial improvement in intelligibility cannot be acquired easily, and the tone quality switching function often remains at the level of the taste of listening of the user of the wireless set.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a wireless receiver which eliminates the problems of the conventional technologies described above and improves intelligibility of reception signals, and a reception method therefor.
It is another object of the present invention to provide a wireless receiver which automatically decreases a noise output level in such a manner as to correspond to a reception field intensity when it receives a weak field signal that generates noise quieting corresponding to the reception field intensity near −120 dBm (near a 12 dB SINAD sensitivity point), and reliably improves intelligibility, and a reception method therefor.
According to one aspect of the present invention for accomplishing these objects, there is provided a wireless receiver including a reception unit for receiving a wireless frequency signal and obtaining a speech band signal; a detection unit connected to the reception unit, for detecting a reception field intensity of the wireless frequency signal on the basis of the speech band signal; and a tone quality control unit for changing the frequency characteristics of the speech band signal from the reception unit in accordance with a detection value of the reception field intensity by the detection unit and outputting a speech band signal having the changed frequency characteristics.
According to one embodiment of the present invention, the tone quality control unit described above includes a first route for passing the speech band signal from the reception unit through a filter, a second route for passing the speech band signal from the reception unit and a selection control unit for selecting the speech band signal outputted from one of the first and second routes in accordance with the detection value of the reception field intensity by the detection unit and outputting the signal so selected from the tone quality control unit.
According to another embodiment of the present invention, the second route of the selection control unit described above passes the speech band signal through means (for example, an attenuator) for changing the signal level of the speech band signal.
According to another embodiment of the present invention, the tone quality control unit described above inclu
Miyakawa Akihisa
Uchimura Kouichi
Yahagi Kazuhiko
Antonelli Terry Stout & Kraus LLP
Appiah Charles N.
Hitachi Denshi Kabushiki Kaisha
Vo Nguyen T.
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