Amplifiers – With semiconductor amplifying device – Including plural amplifier channels
Reexamination Certificate
2003-03-27
2004-11-09
Shingleton, Michael B. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including plural amplifier channels
C330S12400D, C330S296000, C330S285000
Reexamination Certificate
active
06816015
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an amplifier circuit useful, among other things, in wireless devices such as cellular telephones to amplify radio frequency signals.
BACKGROUND OF THE INVENTION
Amplifier circuits are used, among other things, to amplify a radio frequency (RF) signal within a wireless device such as a cellular telephone or personal data assistant. It is known in the art to construct such an amplifier circuit from a number of heterojunction bipolar transistors (HBTs) and also known that HBTs suffer from thermal runaway. See U.S. Pat. Nos. 5,629,648, 5,321,279 and 5,608,353 incorporated herein by this reference. In the '648 and '353 patents, the amplifier circuit includes a number of amplifiers each including an HBT with an emitter coupled to ground, a base, a collector, a base resistor, and a base capacitance in the form of a special segmented capacitor for each HBT to reduce the chances of thermal runaway.
Because the emitters of each HBT are coupled directly to ground, there is no emitter ballasting even though that technique is known to also reduce thermal runaways. See the '648 patent, col. 1, lines 43-50.
In the '279 patent, ballast impedances are added to the bases of an HBT but again, emitter ballasting is not provided for. Other relevant art includes U.S. Pat. No. 5,760,457 and the articles “The Use of Base Ballasting to Prevent the Collapse of Current Gain in ALGaAs/GaAs HBTs”, W. Lui, et al., IEEE Transactions on Electronic Devices, Vol. 43, No. 2, February 1996; “Handbook of III-IV HBTs”, W. Lui, John Wiley and Sons, 1998; and “Horowitz and Hill: The Art of Electronics”, Paul Horowitz, Winfield Hill, Cambridge University Press, NY, N.Y. 1980, also included herein by this reference.
Employing both base and emitter ballasting for the HBTs in accordance with the prior art typically requires a large area circuit resulting in high fabrication costs.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an amplifier with base ballasting and also, preferably, emitter ballasting to fully address thermal runaway.
It is a further object of this invention to provide such an amplifier at a lower cost.
It is a further object of this invention to provide such an amplifier which does not require a large circuit area.
This invention results from the realization that, by grouping HBTs, ballasting is better effected: each HBT has a base resistor selected to offset a portion of the voltage drop across the base and emitter of each transistor and each group of HBTs also has a base resistor selected to offset another portion of the voltage drop so that the base resistor of each HBT does not have to be large enough to provide all of the thermal protection and does not have to dissipate as much power resulting in a more compact layout.
This invention features an improved bipolar transistor power amplifier circuit comprising a bias input node, an RF input node, an RF output node, and a plurality of HBTs. Each HBT includes a base, an emitter, a collector, a base resistor connected to the base and selected to offset a portion of the voltage drop across the base and emitter of each transistor, an emitter resistor connected to the emitter, and a base capacitor having two electrodes one of which is coupled to the base.
The HBTs are grouped together in two or more group each group including a second base resistor selected to offset another portion of the voltage drop across said base and emitter of the transistors. The second base resistors coupled to the bias input node, the collectors of each HBT coupled to the RF output node, and the other electrode of each base capacitor coupled to the RF input node resulting in a power amplifier with HBT base resistors which do not have to provide all of the thermal protection and which do not have to dissipate as much power resulting in a more compact layout.
In one example, there are also two or more third base resistors each connected to a subset of the second base resistors and selected to offset another portion of the voltage drop across said base and emitter of the transistors. In the same example, there is also a resistance in series with a capacitance between the RF input node and the bases of each HBT.
The emitter resistors are optional. Thus, this invention also features an improved bipolar transistor power amplifier circuit comprising a bias input node, an RF input node, an RF output node, a plurality of HBTs each including a base, an emitter, a collector, a base resistor connected to the base and selected to offset a portion of the voltage drop across the base and emitter of each transistor, and a base capacitor having two electrodes one of which is coupled to the base. The HBTs are grouped together in two or more groups, each group including a second base resistor selected to offset another portion of the voltage drop across the base and emitter of the transistors, the second base resistors are coupled to the bias input node, the collectors of each HBT are coupled to the RF output node, and the other electrode of each base capacitor coupled to the RF input node.
The base capacitors are also optional as long as an RF feed network is included that provides high DC isolation between cells while enabling RF energy to be effectively transmitted. Thus, this invention also features an improved bipolar transistor power amplifier circuit comprising a bias input node, an RF input node, an RF output node, a plurality of HBTs each including a base, an emitter, a collector, and a base resistor connected to the base and selected to offset a portion of the voltage drop across the base and emitter of each transistor.
The HBTs grouped are together in two or more groups, each group including a second base resistor selected to offset another portion of the voltage drop across said base and emitter of the transistors. The second base resistors are coupled to the bias input node, and the collectors of each HBT coupled to the RF output node.
In the broadest sense, this invention features a plurality of transistors each comprising a base, an emitter, a collector, and a base resistor connected to the base and selected to offset a portion of the voltage drop across the base and emitter of each transistor. The transistors are grouped together in two or more group, each group including a second base resistor selected to offset another portion of the voltage drop across the base and emitter of the transistors.
This invention also features a method of ballasting the transistors of a power amplifier circuit, the method comprising providing base ballasting for each transistor and selecting a base resistor to offset a portion of the voltage drop across the base and emitter of each transistor, grouping the transistors into two or more groups, and providing additional base ballasting for each group and selecting a base resistor for each group to offset the remaining portion of the voltage drop across the base and emitter of the transistors.
In another example, the method of this invention features adding a base resistor to the base of each transistor and selected to offset a portion of the voltage drop across the base and emitter of each transistor, adding an emitter resistor to the emitter of each transistor, adding a base capacitor having two electrodes one of which is coupled to the base of each transistor, grouping the transistors together in two or more groups, adding a base resistor for each group selected to offset another portion of the voltage drop across the base and emitter of the transistors, connecting the base resistors to a bias input node, connecting the collectors of each transistor to an output node, and connecting the other electrode of each base capacitor to an input node.
REFERENCES:
patent: 3510735 (1970-05-01), Potter
patent: 3577092 (1971-05-01), Kubicz
patent: 3766449 (1973-10-01), Bruchez
patent: 3860460 (1975-01-01), Olson
patent: 3969752 (1976-07-01), Martin et al.
patent: 3977020 (1976-08-01), Enzlin et al.
patent: 3986058 (1976-10-01), Hongu et al.
patent: 3990092 (1976-
McMorrow Robert Jeffery
Zhang Shuyun
Analog Devices Inc.
Iandiorio & Teska
Shingleton Michael B.
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