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Mobile Phone Patent Abstract
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.
Mobile Phone Patent Claims
What is claimed is:
1. 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, the circuit
comprising:
a plurality of damping devices electrically connected in parallel
between the receiving terminal and the low noise amplifier wherein
each damping device has a fixed gain;
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.
2. The circuit of claim 1, wherein a gain damping rate associated
with the circuit increases in steps.
3. 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, the circuit
comprising:
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 linear response to the interference detector; and
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 capacitors
inductively coupled to one another and operatively coupled between
the receiving terminal and the low noise amplifier, the pair of
capacitors damping in a linear relationship the at least one external
interference signal in response to the control voltage signal of
the control voltage generator.
4. The circuit of claim 1, wherein the damping device further includes
a pair of pin diodes respectively operatively coupled between the
pair of capacitors and ground, whereby resistance values respectively
associated with the pair of pin diodes decreases in response to
an increase in voltage associated with the control voltage signal
such that increased current flows through the respective pairs of
capacitors and diodes.
5. The circuit of claim 4, wherein a pair of resistors are respectively
operatively coupled between the control voltage generator and a
junction point between each capacitor and diode pair.
6. The circuit of claim 4, wherein a gain damping rate associated
with the damping device substantially continuously varies in response
to a variation in the control voltage of the control voltage signal.
7. A circuit for at least substantially eliminating at least one
external inference signal from a radio communications signal received
by a code division multiple access (CDMA) mobile phone including
a receiving terminal, the circuit comprising:
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 low noise amplifier circuit operatively coupled to the receiving
terminal, the low noise amplifier circuit including:
an amplifier having an input terminal and an output terminal;
a plurality of switches each operatively coupled between the output
terminal of the amplifier and a corresponding one of a plurality
of feedback resistors respectively operatively coupled between the
plurality of switches and the input of the amplifier, each of said
plurality of switches and said corresponding one of a plurality
of feedback resistors being electrically connected in parallel between
said input and said output terminals of said amplifier; and
a switch driver operatively coupled between the interference detector
and the plurality of switches, 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
on 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.
8. The circuit of claim 7, wherein the amplifier is an operational
amplifier.
9. The circuit of claim 7, wherein the amplifier is a transistor
having a collector terminal for the output terminal and a base terminal
for the input terminal.
10. The circuit of claim 7, wherein a gain damping rate associated
with the circuit increases in steps.
11. 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, the circuit comprising:
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 for generating a control voltage signal in linear response
to the at least one external interference signal detected by the
interference detector; and
a low noise amplifier circuit operatively coupled to the control
voltage generator and the receiving terminal, the low noise amplifier
circuit including:
an amplifier having an input terminal and an output terminal; and
at least one resistor operatively coupled to the output terminal
of the amplifier and to the control voltage generator;
such that a gain associated with the amplifier varies in a linear
relationship in accordance with a control voltage associated with
the control voltage signal applied to the at least one resistor.
12. The circuit of claim 11, wherein the amplifier is an operational
amplifier.
13. The circuit of claim 11, wherein the amplifier is a transistor
having a collector terminal for the output terminal and a base terminal
for the input terminal.
14. The circuit of claim 11, wherein a gain damping rate associated
with the circuit substantially continuously varies in response to
a variation in the control voltage of the control voltage signal.
Mobile Phone Patent Description
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:
If there are generated dual tones with the same amplitude and different
frequencies, the dual tones are expressed by Eq. (2) as:
such that Eo may be further expressed by Eq. (3) as: ##EQU1##
As expressed by Eq. (3), two signals with different frequencies
F1 and F2 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 2F1, 2F2,
F1+F2 and F1-F2. Such signals of the mixed component occur outside
the narrow band of most systems and, therefore, are negligible.
The third order mixing is 2F1+F2, 2F1-F2, 2F2-F1 and 2F2+F1 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 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 for generating
a control voltage signal in response to the at least one external
interference signal detected by the interference detector; and a
low noise amplifier circuit operatively coupled to the control voltage
generator and the receiving terminal, the low noise amplifier circuit,
itself, including an amplifier having an input terminal and an output
terminal; and at least one resistor operatively coupled to the output
terminal of the amplifier and to the control voltage generator;
such that a gain associated with the amplifier varies in accordance
with a control voltage associated with the control voltage signal
applied to the at least one resistor.
These and other objects, features and advantages of the present
invention will become apparent from the following detailed description
of illustrative embodiments thereof, which is to be read in connection
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph illustrating IMD signals versus frequencies;
FIG. 2 is a graph illustrating gain characteristics of the first
and third orders of an external interference signal;
FIG. 3 is a schematic/block diagram of a portion of a CDMA phone
circuit for eliminating external interference signals according
to a first embodiment of the present invention;
FIG. 4 is a graph illustrating a gain damping rate of a damping
circuit versus a control voltage according to the first embodiment
of the present invention;
FIG. 5 is a schematic/block diagram of a portion of a CDMA phone
circuit for eliminating external interference signals according
to a second embodiment of the present invention;
FIG. 6 is a graph illustrating a gain damping rate of a damping
circuit versus a control voltage according to the second embodiment
of the present invention;
FIG. 7 is a schematic/block diagram of a portion of a CDMA phone
circuit for eliminating external interference signals according
to a third embodiment of the present invention;
FIG. 8 is a graph illustrating a gain damping rate of a damping
circuit versus a control voltage according to the third embodiment
of the present invention;
FIG. 9 is a schematic/block diagram of a portion of a CDMA phone
circuit for eliminating external interference signals according
to a fourth embodiment of the present invention; and
FIG. 10 is a graph illustrating a gain damping rate of a damping
circuit versus a control voltage according to the fourth embodiment
of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the attached drawings, same reference numerals are used to represent
parts serving same functions and detailed descriptions are omitted
concerning the parts not essential to describe the inventive concept,
for the sake of convenience.
Two factors are considered in detecting IMD signals in the present
invention. The first is a received signal strength indicator (RSSI)
and the second is a frame error rate (FER) according to the second
service option in the normal communications channel. The service
option is the standard for the loop-back service option of a terminal.
FER is represented by percentage %, calculated in "1-(properly
received frames/all received frames). The RSSI is used to consider
natural losses of the signal power during transmission from the
transmitter to the receiver. Such natural losses include, for example,
path loss, free space attenuation, absorption, fading free space
attenuation, atmospheric absorption, etc. Equations (4) through
(9) which follow, are expressions for the signal power transmitted
from the transmitter to the receiver, and provide the RSSI and FER
to eliminate the external interference signals from an AMPS station.
The power density of a receiving antenna may be expressed by Eq.
(4) as:
Pr=Pt/(4.pi. d.sup.2) (4)
wherein "Pt" represents the level of a signal generated
by the transmitter, and "d" represents the distance between
the transmitter and the receiver. The power PAr received by the
receiving antenna may be expressed by Eq. (5) as:
wherein Aea represents effective area and varies in proportion
to the antenna gain and .lambda./4.pi.. The antenna gain G may be
expressed by Eq. (6) as:
wherein .eta. represents efficiency. The power PAr received by
the receiving antenna may therefore be expressed by Eq. (7) as:
wherein Aea/G is c.sup.2 /4.pi. f.sup.2, the unit of "d"
is kilometers (km), and the unit of "f" is megahertz (MHz).
The gain of a signal transmitted from the transmitter to the receiver
may be expressed by Eq. (8) as:
Further, the free space loss may be expressed in decibels by Eq.
(9) as:
Referring to FIG. 1, it is shown that the third order IMD signals
for dual tone interference are placed in the pass band of the receiver.
The third order IMD can be measured by discovering the input third
order intercept point (IIP.sub.3) in the input terminal. This affects
the low noise amplifier. The IIP.sub.3 defines the gain characteristics
of the first and third order signals for the dual tone signal. Enhancing
the first order signal, the input level is increased owing to the
characteristics of the low noise amplifier, thus saturated.
Referring to FIG. 2, the IMD is increased by the order of 3 dB
for 1 dB increase of the first order signal. Namely, the slope is
1/3. Accordingly, the IMD is increased with the external interference
to break the originally intended signal to be received by a digital
cellular system. Hence, the signal input to the low noise amplifier
should be attenuated in order to reduce the external interference
signals.
As shown in FIG. 3, according to the invention, a CDMA phone includes
a gain variable damping circuit to control the voltage in multisteps.
The CDMA phone includes an antenna 11, a duplexer 18 operatively
coupled to the antenna 11, and a low noise amplifier 13 for amplifying
the received signal to a prescribed level with reducing noises.
The damping circuit includes a plurality of damping devices 121-12n
operatively coupled to the input of the low noise amplifier 13.
Further, the circuit includes a plurality of switches 211-21n respectively
operatively coupled between input terminals of the damping devices
121-12n and the duplexer 18. Still further, an interference detector
15, operatively coupled to the switches 211-21n and the duplexer,
is provided for detecting the external interference signals from
a radio communications signal received through the antenna 11. A
switch driver 14, operatively coupled to the switches 211-21n and
the interference detector 15, is provided for generating a switching
signal to select at least one of the switches 211-21n in accordance
with the detected interference signals.
The interference detector 15 evaluates the degree of interference
by detecting RSSI (Received Signal Strength Indicator); the rate
of average transmission energy per pseudo noise chip (Ec/lo) for
a pilot channel, a synchronous channel, a paging channel, a forward
directional channel and a power control channel; FER (Frame Error
Rate) by the second service option in the forward communication
channel; and so forth. The switches 211-21n are selectively turned
on to vary the gain before the low noise amplifier 13 according
to the measurement of the interference detector 15. The gain damping
rate increases in the form of steps with the control voltage as
shown in FIG. 4.
A second embodiment employs pin diodes as shown in FIG. 5, as compared
with the first embodiment of FIG. 3 which employs the plurality
of the damping devices 121-12n and switches 211-21n, to set the
gain. In this embodiment, the damping device 25 consists of an inductor
coil (preferably, .lambda./4) L connected between the duplexer 18
and the input of the low noise amplifier 13, pin diodes D1 and D2
respectively connected through capacitors C1 and C2, and resistors
R1 and R2 connecting the nodes of the capacitors and pin diodes
with a control voltage generator 23, which generates a control voltage
Vt applied to the nodes according to the interference measurement
of the interference detector 15 operatively coupled thereto. The
signal transferred from the duplexer 18 to the input of the low
noise amplifier 13 is damped by the capacitors C1 and C2, as shown
in FIG. 6. Namely, the capacitors C1 and C2 are grounded through
the pin diodes D1 and D2 in order to provide such damping. The diodes
D1 and D2 increase the current flow as the control voltage Vt increases,
thus reducing their resistances. The gain damping rate of the damping
device continuously increases with an increase of the control voltage,
as shown in FIG. 6.
A third embodiment of the present invention employs a transistor
for providing low noise amplification whereby a feedback resistance
of the transistor is switched in order to vary the gain associated
therewith, as shown in FIG. 7. Specifically, a low noise amplifier
52 consists of an amplifying transistor TR having a base terminal,
a collector terminal and an emitter terminal. The collector terminal
is operatively coupled to first terminals of a plurality of switches
311-31n. Second terminals of the switches 311-31n are respectively
operatively coupled to first terminals of a plurality of resistors
R3-Rn. Second terminals of resistors R3-Rn are operatively coupled
to the base terminal of transistor TR. The emitter terminal is grounded.
The switches 311-31n are selectively turned on, respectively, in
response to a switching signal generated by a switch driver 35,
operatively coupled thereto, according to the interference measurement
of the interference detector 15, operatively coupled to the duplexer
18, the switch driver 35 and the resistors R3-Rn, so that the feedback
resistance is varied to control the amplifying level, thus resulting
in the desired damping. The transistor TR may be an operational
amplifier. Nonetheless, with respect to the embodiment of FIG. 7,
the gain damping rate of the low noise amplifier increases with
the control voltage in the form of steps, as shown in FIG. 8.
A fourth embodiment of the CDMA phone also employs a transistor
TR in a low noise amplifier 50 in order to provide the low noise
amplification, as shown in FIG. 9. However, in this case, the gain
varies continuously with the control voltage, as compared to the
third embodiment as shown in FIG. 7, where the gain is set in the
form of steps as shown in FIG. 8. The control voltage Vt is supplied
from the control voltage generator 24, operatively coupled between
the interference detector 15 and the amplifier 50, through a load
resistor RA of the transistor TR, depending on the interference
measurement of the interference detector 15. Resistor RB provides
feedback between the collector and base terminals of transistor
TR. Again, the emitter terminal is grounded. The control voltage
Vt is controlled to adjust the gain since the gain of the transistor
TR may be reduced by lowering the source voltage, i.e., control
voltage Vt. The gain damping rate of the low noise amplifier 50
continuously increases with the control voltage, as shown in FIG.
10.
Thus, the inventive CDMA phone with a damping circuit as described
herein advantageously eliminates or at least substantially eliminates
the external interference signals generated from an AMPS station
such that only CDMA signals are processed by the CDMA phone. As
a result, communications errors, otherwise caused by the interference,
are prevented or at least substantially prevented even in the area
of the AMPS station.
Although illustrative embodiments of the present invention have
been described herein with reference to the accompanying drawings,
it is to be understood that the invention is not limited to those
precise embodiments, and that various other changes and modifications
may be affected therein by one skilled in the art without departing
from the scope or spirit of the invention.
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