Low-noise amplifier

Details Low-noise amplifier Low-noise amplifier

1999-06-10

2001-03-27

Mottola, Steven J. (Department: 2817)

Amplifiers

Combined with automatic amplifier disabling switch means

C330S12400D

Reexamination Certificate

active

06208203

ABSTRACT:

Hereby incorporated by reference are Korean priority applications 1998-21613, 1998-27169 and 1999-8688.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an amplifier circuit, and more particularly, to a low-noise amplifier circuit typically used for a wireless communications equipment.
2. Description of the Related Art
In a radio frequency (RF) signal receiving apparatus such as a cellular phone and a base station of a wireless communication system, a received signal has very weak intensity and includes considerable noise mixed therein. Accordingly, such a signal receiving apparatus requires a circuit for amplifying the received signal while reducing a noise figure of the signal. A low-noise amplifier, which is typically installed in an input stage of the signal receiving apparatus, amplifies the input RF signal so that an amplified signal has a required gain and noise figure.
As illustrated in
FIG. 1
, a conventional low-noise amplifier
10
includes an amplifying circuit
14
performing an amplification of the RF signal and impedance matching circuits
12
and
16
for matching impedances between the amplifying circuit
14
and external circuits. The input and output impedance matching circuits
12
and
16
are designed based on scattering parameters (S-parameters) so that reflection coefficients are minimized at input and output stages of the amplifier. Meanwhile, since the low-noise amplifier determines the overall noise characteristics of the signal receiving apparatus, the amplifier is usually designed in a balanced type rather than a single-ended type so as to have a minimum noise figure.
As shown in
FIG. 2
, a balanced type low-noise amplifier includes at least one amplifying stage, a power supply for providing DC power to the amplifying stage, hybrid couplers for splitting or combining signals at input and output stages, delay compensating circuits for compensating phase difference between the signal paths existing between the hybrid couplers, a noise removing circuit for reducing noise, and a comparator for comparing a signal or a supply voltage with a reference. In particular, the power supply can be implemented in various manners to procure an optimum amplification.
If any one of the internal circuits of the amplifying circuit happens to be damaged or the supply voltage is lost, the amplifying circuit cannot operate properly. In such a case, the signal receiving apparatus or the overall communication system happens to be faced with a significant signal loss. Meanwhile, when the low-noise amplifier cannot operate normally, the comparator in the amplifying circuit may detect the abnormality to notify a user via a light emitting diode so that the user replaces or troubleshoots the amplifying circuit. However, in a critical situation, the system may be inoperable at all until the user or a maintenance personnel replaces or troubleshoots the amplifying circuit.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a low-noise amplifier which is equipped with at least one redundancy circuit which is connected in parallel to an amplifying circuit, so that the low-noise amplifier operates without a significant signal loss even when an abnormality takes place in the amplifying circuit and the amplifying circuit is not replaced or troubleshooted yet.
In order to achieve the above object, a low-noise amplifier according to the present invention includes a redundancy circuit effectively operable instead of an amplifying circuit when the amplifying circuit is in an abnormal condition, and at least one switch for activating the redundancy circuit when the amplifying circuit is abnormal. In a preferred embodiment, the redundancy circuit includes a transmission line for bypassing an input RF signal when the amplifying circuit is in an abnormal condition. In an alternative, the redundancy circuit includes a redundant amplifying circuit, so that the redundant amplifying circuit amplifies the input RF signal in place of the amplifying circuit.
According to the present invention, the low-noise amplifier is operable without a significant signal loss when the main amplifying circuit has an abnormality and cannot operate effectively. Thus, it is possible to prevent the communication system employing the circuit from being inoperable even when any one of the internal circuits of the amplifying circuit happens to be damaged or the supply voltage is lost. Accordingly, the reliabilities of the low-noise amplifier and the communication system are enhanced.


REFERENCES:
patent: 4298844 (1981-11-01), Shimp
patent: 4780685 (1988-10-01), Ferguson
patent: 5418490 (1995-05-01), Kaegebein
patent: 5659267 (1997-08-01), Buer et al.
patent: 5909643 (1999-06-01), Aihara
patent: 5973557 (1999-10-01), Miyaji et al.
patent: WO 91/19349 (1991-12-01), None

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