Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
1998-07-29
2001-05-29
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S285000
Reexamination Certificate
active
06239659
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a gain-controlled RF signal amplifier circuit according the the preamble of claim
1
particularly useful for high frequencies up to the range of microwave frequencies.
BACKGROUND OF THE INVENTION
Conventional gain-controlled amplifiers of the above mentioned general type have at least one of the following drawbacks, i.e.
they require high supply power and are thus not suitable for battery powered units;
they are not suitable for high operating frequencies;
the signal handling capability in particular in respect to linearity is degraded if the gain is reduced; and/or such amplifiers
exhibit poor noise figures.
The objects of the invention are to eliminate such problems and to provide a gain-controlled RF signal amplifier suitable for high operating frequencies in the GHz range with good operating linearity, in particular if the gain is reduced, having low noise figure and low power consumption.
These objects are solved according to the invention by a gain-controlled RF signal amplifier provided with an adaptively controlled feedback network according to the characterizing part of claim
1
.
Advantageous amendments, improvements and/or embodiments of the subject matter of claim
1
are defined by dependent claims, are described in the following part of this specification and/or are within the scope of the skill of the average expert after having educated himself/herself by reading the present disclosure of the invention.
Variable gain RF amplifiers with more or less linear gain control are known in the art, e.g. in a certain configuration using a dual-gate FET wherein the second gate is used for gain control.
EP-A2-0 601 888 discloses a gain-controlled RF amplifier using a PIN-diode in a series feedback circuit. A similar structure for a gain-controlled RF amplifier using a PIN-diode as a load altering resistance is the subject matter of U.S. Pat. No. 4,275,362. U.S. Pat. No. 4,057,765 describes a variable gain RF input amplifier in which the first 10 dB of a signal attenuation are effected by an AGC voltage applied to the amplification transistor followed by a supplementary attenuation by an increasing reverse bias applied to a PIN-diode in the signal input path to the amplification transistor. The PIN-diode in this circuit is only used as a direct regulation means for higher attenuation values.
Other examples of gain-controlled RF signal amplifiers, more remote from the invention, are the subject matters of U.S. Pat. No. 4,147,991 and U.S. Pat. No. 4,019,160.
SUMMARY OF THE INVENTION
With the invention, the following problems are eliminated: Due to the adaptively controlled feedback network, preferably used in connection with a bipolar transistor or a FET in common emitter or source reference potential connection, respectively, the transistor and the controlling network can be operated at low voltage and current levels, e.g. 3 V and 2 mA. Even for operating frequencies of 1 GHz and above a gain control range of more than 20 dB can be obtained. Due to the novel feedback structure, the linearity is enhanced especially for low gain values. The controlled feedback does not degrade the noise figure. If used in an AGC loop, for example in the entrance part of a digital audio broadcast (DAB) receiver, the circuit current is increased for high input levels. Therefore, the proposed circuit is particularly suitable for battery powered receiver input stages with gain control.
Since the amplifying transistor is preferably operated in grounded emitter configuration (grounded source configuration for a FET), the highest maximum gain with low noise figure is achievable.
Different from gain control circuits described in the above prior art documents, according to the invention a DC-coupled parallel feedback circuit is used. This allows for high-frequency operation and improves the linearity for reduced gain settings. For reduced gain, the current through the amplifier transistor is increased. This further increases the input signal handling capability and the linearity of the amplifier.
An advantageous and satisfyingly tested embodiment of a gain-controlled RF signal amplifier circuit with features according to the invention is subsequently described with reference to the accompanying drawings. However, this description of the embodiment is not to be understood as limitation to the inventive concept, the scope of which is defined as the subject matter of claim
1
including equivalent circuit designs thereof and advantageous improvements thereof.
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patent: 3098199 (1963-07-01), Carney et al.
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patent: 3723894 (1973-03-01), Benenati
patent: 4114105 (1978-09-01), Duncan
patent: 4275361 (1981-06-01), Schurmann
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patent: 5546050 (1996-08-01), Florian et al.
patent: 5646573 (1997-07-01), Bayruns et al.
patent: 0 734 118 A1 (1996-09-01), None
Kobayashi, K.W. et al: “Monolithic GAAS HBT P-I-N Diode Variable Gain Amplifiers, Attenuators, and Switches” IEEE Transactions on Microwave Theory and Techniques, vol. 41, No. 12, Dec. 1, 1993, pp. 2295-2302, XP000426147.
Kobayashi, K. W. et al: “A Novel Monolithic HBT-P-I-N-HEMT Integrated Circuit with HBT Active Feedback and P-I-N Diode Variable Gain Control” IEEE Transactions on Microwave Theory and Techniques, vol. 43, No. 5, May 1, 1995, pp. 1004-1009, XP000502058.
G. W. Short, The D. C. Feedback Pair, Wireless World p. 637, Dec. 1961.
Chang Dexter T.
Choe Henry
Frommer William S.
Frommer Lawrence & Haug LLP.
Pascal Robert
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