Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1997-10-24
2001-05-08
Patel, Ajit (Department: 2662)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S419000, C370S465000, C375S254000, C375S346000, C333S012000, C455S234100, C455S283000
Reexamination Certificate
active
06229797
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a code division multiple access (CDMA) mobile phone in a digital communications system and, more particularly, to a circuit for eliminating external interference signals in such a mobile phone.
2. Description of the Related Art
Generally, a digital communications system may be designed to employ CDMA and an advanced mobile phone service (AMPS) which employs frequency modulation. The CDMA cellular system is usually used in dual mode to allow reception of an analog signal. Namely, the system may be used not only in CDMA mode but also in AMPS mode. However, in this case, when communicating in digital signals, there often occurs analog interfering signals which cut a call signal or cause an error in the received digital signals. This error is called intermodulation distortion (IMD), which affects a CDMA mobile phone near an AMPS radio station. A strong external interference signal overloads the low noise amplifier of the CDMA phone so that the IMD component strongly interferes with the CDMA frequency band, causing it to be off-line. An exemplary description of the influence of such interference signals will now be provided.
The received interference signals pass through the low noise amplifier of a conventional CDMA phone to produce second and third order harmonics Eo, which may be expressed by Eq. (1) as:
Eo=k
1
Ei+k
2
Ei
2
+k
3
Ei
3
(1)
If there are generated dual tones with the same amplitude and different frequencies, the dual tones are expressed by Eq. (2) as:
Ei=A
(
cos &ohgr;
1
t+cos &ohgr;
2
t
) (2)
such that Eo may be further expressed by Eq. (3) as:
E
o
=
k
1
A
(
cos
ω
1
t
+
cos
ω
2
t
)
+
k
2
A
2
(
cos
ω
1
t
+
cos
ω
2
t
)
2
+
k
3
A
3
(
cos
ω
1
t
+
cos
ω
2
t
)
3
=
k
2
A
2
+
k
2
A
2
(
ω
1
-
ω
2
)
t
+
(
k
1
A
+
9
k
3
A
3
/
4
)
cos
ω
1
t
+
(
k
1
A
+
9
k
3
A
3
/
4
)
cos
ω
2
t
+
3
k
3
A
3
/
4
cos
(
2
ω
1
-
ω
2
)
t
+
3
k
3
A
3
/
4
cos
(
2
ω
2
-
ω
1
)
t
+
k
2
A
2
cos
(
ω
1
+
ω
2
)
t
+
k
2
A
2
/
2
cos
2
ω
1
t
+
k
2
A
2
/
2
cos
2
ω
2
t
+
3
k
3
A
3
/
4
cos
(
2
ω
1
+
ω
2
)
t
+
3
k
3
A
3
/
4
cos
(
2
ω
2
+
ω
1
)
t
+
k
3
A
3
/
4
cos
3
ω
1
t
+
k
3
A
3
/
4
cos
3
ω
2
t
(
3
)
As expressed by Eq. (3), two signals with different frequencies F
1
and F
2
are amplified to generate non-linear components in the form of the products obtained by multiplying the mixed forms of the second and third orders. The second order mixing is 2F
1
, 2F
2
, F
1
+F
2
and F
1
−F
2
. Such signals of the mixed component occur outside the narrow band of most systems and, therefore, are negligible. The third order mixing is 2F
1
+F
2
, 2F
1
−F
2
, 2F
2
−F
1
and 2F
2
+F
1
whose signals cause IMD to occur in the pass band of most systems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a circuit for eliminating or at least substantially eliminating external interference signals generated from AMPS stations in a CDMA mobile phone in order to prevent or at least substantially prevent communication errors such as cutting of a call within the area affected by the AMPS station.
In one aspect of the invention, a circuit for at least substantially eliminating at least one external interference signal from a radio communications signal received by a code division multiple access (CDMA) mobile phone including a receiving terminal and a low noise amplifier comprises: a plurality of damping devices operatively coupled between the receiving terminal and the low noise amplifier; a plurality of switches respectively operatively coupled between the plurality of damping devices and the receiving terminal; an interference detector operatively coupled to the receiving terminal for detecting the at least one external interference signal from the received radio communications signal; and a switch driver operatively coupled between the plurality of switches and the interference detector, the switch driver generating a switching signal in response to the interference detector to select at least one of the switches in accordance with the at least one detected interference signal in order to vary a gain associated with the received communications signal in accordance with at least one of the damping devices.
In another aspect of the invention, a circuit for at least substantially eliminating at least one external interference signal from a radio communications signal received by a code division multiple access (CDMA) mobile phone including a receiving terminal and a low noise amplifier comprises: an interference detector operatively coupled to the receiving terminal for detecting the at least one external interference signal from the received radio communications signal; a control voltage generator operatively coupled to the interference detector, the control voltage generator generating a control voltage signal in response to the interference detector; a damping device operatively coupled between the receiving terminal and the low noise amplifier and operatively coupled to the control voltage generator, the damping device including a pair of capacitive elements inductively coupled to one another and operatively coupled between the receiving terminal and the low noise amplifier, the pair of capacitors damping the at least one external interference signal in response to the control voltage signal of the control voltage generator.
In yet another aspect of the inventions a circuit for at least substantially eliminating at least one external interference signal from a radio communications signal received by a code division multiple access (CDMA) mobile phone including a receiving terminal comprises: an interference detector operatively coupled to the receiving terminal for detecting the at least one external interference signal from the received radio communications signal; and a low noise amplifier circuit operatively coupled to the receiving terminal. The low noise amplifier circuit, itself, including: an amplifier having an input terminal and an output terminal; a plurality of switches operatively coupled between the output terminal and the input terminal of the amplifier; and a plurality of feedback resistors respectively operatively coupled between the plurality of switches and the input of the amplifier. The circuit for at least substantially eliminating at least one external interference signal further comprises a switch driver operatively coupled between the interference detector and the plurality of switches of the low noise amplifier circuit, the switch driver generating a switching signal in response to the external interference signal detected by the interference detector and the switching signal selecting at least one of the plurality of switches and thus at least a respective one of the plurality of feedback resistors such that the amplifier of the low noise amplifier circuit amplifies the received radio communications signal with low noise.
In still a further aspect of the invention, a circuit for at least substantially eliminating at least one external interference signal from a radio communications signal received by a code division multiple access (CDMA) mobile phone including a receiving terminal comprises: an
Dilworth & Barrese LLP
Patel Ajit
Pezzlo John
Samsung Electronics Co., Inc.
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