Reception circuit

Details Reception circuit Reception circuit

1998-12-14

2002-02-26

Pham, Chi (Department: 2631)

Pulse or digital communications

Receivers

Interference or noise reduction

Reexamination Certificate

active

06351504

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reception circuit, and particularly to a reception circuit for use with a code-division-multiple-access (hereinafter referred to as a CDMA) system portable telephone and in which a high-frequency amplifying unit and an intermediate-frequency amplifying unit amplify a variable gain of a reception signal such that a reception signal level satisfies a predetermined standard.
2. Description of the Prior Art
Recently, as portable telephones are rapidly widespread, the number of communication channels is becoming short. Therefore, it is considered that a frequency modulation (FM)-system portable telephone is moved to a CDMA-system portable telephone in which many channel numbers can be maintained. In the U.S.A, as the FM-system (AMPS system in U.S.A) portable telephone is moved to the CDMA-system portable telephone, a CDMA/AMPS dual mode-system portable telephone in which the AMPS system portable telephone and the CDMA-system portable telephone coexist within the same signal bands is proposed and about to be put in practical use.
In this case, the FM-system portable telephone has not only a narrow range in which power of a transmission signal can be controlled upon signal transmission, but unsatisfactory accuracy of transmission frequencies. In the CDMA-system portable telephone, when a reception signal level exceeds a constant level due to the influence of a large disturbance signal, there occurs a call drop (call drop). Therefore, in the CDMA/AMPS dual mode system portable telephone, it is necessary to protect the CDMA system from being largely affected by mutual modulation disturbance of the AMPS system. Accordingly, in the U.S.A, the IS-95 is specified as a performance standard for mutual modulation disturbance in the CDMA system. According to the IS-95, there are standardized disturbance signal levels in which the reception signal level is −101 dBm, −90 dBm and −79 dBm.
The portable telephone of the known CDMA/AMPS dual mode system adopts a means (hereinafter referred to as a first means) using an automatic gain amplifier in a high-frequency state of a reception circuit to adjust the automatic gain amplifier in response to a reception signal level and a means (hereinafter referred to as second means) using a low-noise high-frequency amplifier in the high-frequency stage of the reception circuit and a reception signal bypass circuit for selectively bypassing the low-noise high-frequency amplifier to place the reception signal bypass circuit in a connected state or in a non-connected state in response to the reception signal level.
FIG. 4
is a block diagram showing an example of a known CDMA/AMPS dual mode system portable telephone, and mainly shows a reception circuit unit in which the aforementioned first means is adopted in the high-frequency stage of the reception circuit.
As shown in
FIG. 4
, the CDMA/AMPS dual mode system portable telephone comprises: a reception circuit unit composed of an attenuator
31
, an automatic gain high-frequency amplifier
32
, a bandpass filter
33
, a frequency converter
34
, a CDMA filter
35
, an AMPS filter
36
, a change-over switch
37
, an intermediate-frequency amplifier
38
, a QPSK demodulator
39
and a control voltage generating unit
40
; a transmission circuit unit composed of a transmission signal forming circuit
41
; and a transmission and reception common circuit unit composed of a duplexer
42
, a transmission and reception unit
43
, a local oscillator
44
and a control unit
45
.
Then, in the reception circuit unit, the attenuator
31
has an input terminal connected to an output terminal of the duplexer
34
and an output terminal connected to an input terminal of the automatic gain high-frequency amplifier
32
. The automatic gain high-frequency amplifier
32
has an output terminal connected to an input terminal of the bandspass filter
33
. The bandpass filter
33
has an output terminal connected to a first input terminal connected to the frequency converter
34
. The frequency converter
34
has a second input terminal connected to an output terminal of the local oscillator
43
and an output terminal connected to respective input terminals of the CDMA filter
35
and the AMPS filter
36
. The change-over switch
37
has two fixed contacts connected to respective output terminals of the CDMA filter
35
and the AMPS filter
36
and has a movable contact connected to an input terminal of the intermediate-frequency amplifier
38
. The intermediate-frequency amplifier
38
has an output terminal connected to an input terminal of the QPSK demodulator
39
, and the QPSK demodulator
39
has an output terminal connected to the control unit
45
. The control voltage generating unit
40
has an input terminal connected to the control unit
45
and an output terminal connected to a control terminal of the automatic gain high-frequency amplifier
32
. In the transmission circuit unit, the transmission signal forming circuit
41
has an input terminal connected to the control unit
45
, an output terminal connected to the input terminal of the duplexer
42
and a second input terminal connected to the local oscillator
44
. Further, in the transmission and reception common circuit, the duplexer
42
has an input and output terminal connected to the transmission and reception antenna
43
.
Also,
FIG. 5
is a block diagram showing an example of a known CDMA/AMPS dual mode system portable telephone, and mainly shows the reception circuit unit in which the aforementioned second means is used in the high-frequency stage of the reception circuit.
Having compared the CDMA/AMPS dual mode system portable telephone (hereinafter referred to a second example) according to this example shown in
FIG. 5
with the CDMA/AMPS dual mode system portable telephone (hereinafter referred to as a first example) of the preceding example shown in
FIG. 4
, it is to be noted that the first example differs from the second example only in that, while the first example includes the attenuator
31
and the automatic gain high-frequency amplifier
32
in the reception circuit unit, the second example includes a low-noise high-frequency amplifier
46
and a reception signal bypass circuit
47
selectively connected to the low-noise high-frequency amplifier
46
in parallel, and the first example and the second example are not different from each other in arrangement. Therefore, the circuit arrangement of the second example need not be described more.
Next,
FIG. 6
is a characteristic graph showing a C/N (carrier-to-noise ratio) relative to reception signal levels in the first example and the second example of the known CDMA/AMPS dual mode system portable telephone.
FIG. 7
is a characteristic graph showing a disturbance signal level relative to reception signal levels in the first example and the second example of the known CDMA/AMPS dual mode system portable telephone.
In
FIG. 6
, a vertical axis represents a C/N expressed by dB, and a horizontal axis represents a reception signal level expressed by dBm. In
FIG. 7
, a vertical axis represents a disturbance signal level expressed by dBm, and a horizontal axis represents a reception signal level expressed by dBm.
A characteristic curve L
1
in
FIGS. 6 and 7
represents a characteristic of the first example, and a characteristic curve L
2
represents a characteristic of the second example, a straight line LT in
FIG. 6
represents a target line in the C/N, and a straight line LS in
FIG. 7
represents a reference line in the IS-95.
An outline of an operation of the first example of the known CDMA/AMPS dual mode system portable telephone is as follows.
A transmission signal formed by the control unit
44
is supplied through the transmission signal forming circuit
41
of the transmission circuit unit to the duplexer
42
and supplied from the duplexer
42
to the transmission and reception antenna
43
, and is transmitted from the transmission and reception antenna
43
. Also, a reception signal r

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