Active operating point adjustment for power amplifiers

Details Active operating point adjustment for power amplifiers Active operating point adjustment for power amplifiers

2000-02-22

2001-07-03

Mottola, Steven J. (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including temperature compensation means

C330S296000, C330S307000

Reexamination Certificate

active

06255910

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an amplifier circuit containing at least one output stage transistor, a circuit for compensating for quiescent current drifts and optionally components for driving the output stage transistor(s).
Amplifier circuits for radiofrequency technology generally contain output stage transistors, such as e.g. GaAs-MESFETs. By way of example, the operating point of the output stage of a mobile telephone is adjusted to a region of the gain characteristic which lies in the lower third of the drain-source current I
DS
, typically at approximately I
DS
=0.1×I
DSS
(class AB operation).
Suitable amplifier circuits with high efficiency generally contain, on one chip, a plurality of MESFETs having a multiplicity of elongate doping regions. During fabrication, slight production-dictated fluctuations (e.g. due to varying doping concentration) may occur from chip to chip or from wafer to wafer, the fluctuations resulting in gain characteristics that are not exactly reproducible. Therefore, it is necessary to subsequently adjust the quiescent current for each individual chip. This is done by adjusting the so-called “pinch-off” voltage v
p
in a range of from e.g. −4 V to −2.5 V, with the result that I
DS
lies within a predetermined range of e.g. I
DS
=10% I
DSS
±10%. An additional difficulty resides in the fact that the limit value for the quiescent current must be adhered to in the entire temperature range of from −30° C. to 80° C., for example. Complicated optimization of the quiescent current by subsequent calibration of the finished circuit is therefore customary. However, corresponding calibration is cost-intensive and complicated.
Active operating point adjustment for power amplifiers is likewise disclosed in Published, British Patent Application GB 2 307 155 A, Published, European Patent Application 0 529 421 A, an article by M. T. Schmidl et al., titled “Low Overhead, Low Complexity Burst Synchronization for OFDM”, 1996 IEEE, Bd. 3, Pgs. 1301-1306, and an article by B. Stantchev et al., titled “Burst Synchronization for OFDM-Bade Cellular Systems With Separate Signaling Channel”, VTC '98. 48
th
IEEE, Pgs 758-762, vol. 2.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an active operating point adjustment for power amplifiers which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which does not have to be subsequently calibrated and has a quiescent current lying within the predetermined limits over a significantly extended temperature range.
With the foregoing and other objects in view there is provided, in accordance with the invention, an amplifier circuit, including a common chip area; at least one output stage transistor having electrodes and disposed on the common chip area; and a circuit for compensating for quiescent current drifts having at least one reference current field-effect transistor with a gate electrode, the gate electrode is disposed in a region of the electrodes of the output stage transistor and at a distance of less than 100 &mgr;m from a nearest one of the electrodes of the output stage transistor.
The reference current transistor according to the present invention is configured in such a way that it models as well as possible the external electrical and physical influences on the output stage transistors, which influences act on the quiescent current. The reference current transistor is preferably at the same electrical potential as the output stage transistor.
The amplifier circuit according to the invention preferably has a quiescent current that lies in a range of from 10 to 500 mA in the temperature range of from −30° C. to 80° C.
The gate electrode is preferably situated at a distance of less than 100 &mgr;m from the nearest electrode of an output stage transistor(s). The gate electrode is particularly preferably disposed at a distance of less than 50 &mgr;m.
A transistor that preferably corresponds to the greatest possible extent to the configuration of the output stage transistor is used as the reference current transistor. In particular both kinds of transistors are fabricated using GaAs-MESFET technology. It is particularly expedient, during the fabrication of the circuit, to concomitantly use a partial region of the doping regions of the output stage transistor for the reference current transistor. In other words, one or more doping regions which are provided for the output stage transistors is or are used for forming a reference current transistor.
The current of the reference current transistor is preferably used for regulating the input signal of the output stage transistor(s).
In a preferred embodiment, the circuit for compensating for quiescent current drifts is not disposed on the chip on which the output stage transistors are situated.
Preferably, the circuit for compensating for quiescent current drifts, with the assistance of a largely constant reference voltage and a resistor, forms a voltage that is proportional to the current of the reference current transistor(s). This voltage is then used for regulating the input signal of the output stage transistor(s).
For regulating the input signal of the output stage transistor(s), the circuit for compensating for quiescent current drifts preferably has at least one transistor. This transistor is particularly preferably a bipolar transistor, in particular a PNP transistor using bipolar technology.
Furthermore, the circuit for compensating for quiescent current drifts expediently has an additional circuit configuration, which compensates for temperature drifts of the compensation circuit which are additionally present.
The present invention further relates to the use of the amplifier circuit according to the invention as a power amplifier in mobile radio systems, such as mobile telephones for example.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an active operating point adjustment for power amplifiers, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.


REFERENCES:
patent: 5216383 (1993-06-01), Uittenbogaard et al.
patent: 5952886 (1999-09-01), Buer et al.
patent: 6046642 (2000-04-01), Brayton et al.
patent: 0 529 421 A2 (1993-03-01), None
patent: 0 529 421 B1 (1993-03-01), None
patent: 2 307 155 (1996-11-01), None
Non-Patent Document “Rahmen-/Takt-und Frequenzsynchronisation . . . ”, chapter 5, pp. 53-71, pertains to the frame-/cycle-and frequencesynchronization for a OFDM system.
Non-Patent Document “Low-Overhead, Low-Complexity [Burst] Synchronization for OFDM” ((Schmidl et al.), dated Jun. 23, 1996, XP 000625022, pp. 1301-1306.
Non-Patent Document “Burst Synchronization for OFDM-based cellular systems . . . ” (Stantchev et al.), dated 1998, XP-002089525 pp. 758-762.

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