Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
2000-12-28
2004-04-13
Tran, CongVan (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S232100, C455S251100, C455S127200, C330S127000, C330S296000, C330S278000, C330S285000
Reexamination Certificate
active
06721549
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Low-Noise Amplifier for a Mobile Communication Terminal” filed in the Korean Industrial Property Office on Dec. 29, 1999 and assigned Ser. No. 99-65239, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a mobile communication terminal, and in particular, to a low-noise amplifier for amplifying a received signal in a mobile communication terminal.
2. Description of the Related Art
FIG. 1
is a block diagram illustrating a receiver for a conventional mobile communication terminal.
Referring to
FIG. 1
, upon receipt of a radio signal, an RSSI (Received Signal Strength Indicator) detector
310
detects field strength of the received signal and provides information on the detected field strength to an automatic gain control (AGC) amplifier controller
320
. The AGC amplifier controller
320
compares the detected field strength information provided from the RSSI detector
310
with a predetermined field strength value. If the detected field strength is lower than or equal to the predetermined field strength, the AGC amplifier controller
320
provides a power-up command to an AGC amplifier
360
and a low-noise amplifier (LNA) controller
330
in order to increase a power level of the received signal.
The low-noise amplifier controller
330
then provides a first bias circuit
150
with a preset voltage in order to enable a low-noise amplifier
100
. The first bias circuit
150
generates a bias voltage according to the preset voltage provided from the low-noise amplifier controller
330
and provides the generated bias voltage to a base of a bipolar junction transistor (BJT)
140
. Then, the BJT
140
is turned ON in response to the bias voltage and a current flowing through the BJT
140
is amplified and matched through an input matching circuit
120
and an output matching circuit
130
. The output of the output matching circuit
130
is provided to a down-converter
340
. The down-converter
340
mixes a local oscillation frequency provided from a local oscillator
350
with the received signal amplified by the low-noise amplifier
100
. AGC amplifier
360
amplifies the signal output from the down-converter
340
to a predetermined level and outputs the amplified signal in an intermediate frequency (IF).
As shown in
FIG. 1
, the receiver with the Si BJT has increased current consumption due to the turn-on voltage. In particular, when the Si BJT is used for the low-noise amplifier, the noise factor characteristic is degraded. Further, a gain of the Si BJT is significantly variable depending on the current and the Si BJT consumes a comparatively large current to maintain its linearity, as compared with an GaAs MESFET (Metal Semiconductor Field-Effect Transistor). Particularly, in a mobile communication system using a high frequency (e.g., at around 2 GHz) such as PCS (Personal Communication System) or IMT-2000 system, the receiver generally uses a 2-stage low-noise amplifier. When using a plurality of low-noise amplifiers, the receiver has greatly increased current consumption due to an increase in number of Si BJTs used.
FIG. 2
is a detailed circuit diagram illustrating a modified low-noise amplifier for the receiver in the conventional mobile communication terminal.
Referring to
FIG. 2
, a received signal is applied to the input matching circuit
120
and the signal matched by the input matching circuit
120
is applied to a gate of a MESFET
230
, the gate being connected to a self-bias resistor
200
. A source bias resistor
220
is set to a specific resistance to maintain linearity. A capacitor
260
connected to the source of the MESFET
230
and a capacitor
240
connected to the drain of the MESFET
230
are used as a bypass capacitor. A drain of the MESFET
230
is connected to the power supply voltage Vdd through an inductor
250
. A signal at the drain of the MESFET
230
is matched by the output matching circuit
130
. However, the receiver with the MESFET, generally, must provide a negative voltage to the gate of the MESFET as a bias voltage, and a separate negative voltage generator is therefore needed to provide the negative voltage. Therefore, as shown in
FIG. 2
, a positive voltage being provided to the source through the source bias resistor
220
on a self-bias basis is used as a gate bias voltage. However, when the gate voltage is controlled by using the source bias resistor
220
, there is a limitation in controlling the current because the source bias resistor
220
has a fixed resistance.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a low-noise amplifier with minimized current consumption.
It is another object of the present invention to provide a low-noise amplifier which can maintain linearity with the least current consumption.
To achieve the above and other objects, there is provided a low-noise amplifier for a mobile communication terminal. In the low-noise amplifier, a low-noise amplifier controller receives a signal-to-noise ratio (SNR) of a received signal, and outputs a control signal of a preset voltage when the SNR is lower than a predetermined SNR. A bias circuit increases a bias current according to the control signal output from the low-noise amplifier controller. A low-noise amplifier amplifies the received signal to a preset level according to the bias current provided from the bias circuit.
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patent: 5517684 (1996-05-01), Fujita et al.
patent: 5889821 (1999-03-01), Arnstein et al.
patent: 6208203 (2001-03-01), Jung et al.
patent: 6240126 (2001-05-01), Ohashi et al.
patent: 6311048 (2001-10-01), Loke
patent: 6356745 (2002-03-01), Lee et al.
patent: 6498926 (2002-12-01), Ciccarelli et al.
patent: 6556559 (2003-04-01), Mitsume et al.
Cho Seung-Ki
Lee Jae-Min
Lee Woo-Yong
Park Se-Young
Dilworth & Barrese LLP
Tran CongVan
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