Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
2000-06-14
2004-05-11
Trost, William (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S126000, C455S127500, C330S285000, C330S136000
Reexamination Certificate
active
06735424
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally concerns amplifier design and amplifier operation, particularly for wireless cellular radio communications applications where occasional jamming is prevalent.
The present invention particularly concerns the realization by both design and operation of a Low Noise Amplifiers (LNA) simultaneously improved in (i) dynamic range and (ii) overall power consumption, these seemingly contradictory requirements being satisfied by optimizing power consumption in the LNA in consideration of its instant operating environment.
The present invention further particularly concerns an ungrounded power detector that is both fast and sensitive to detect the output power of, for example, a LNA.
2. Description of the Prior Art
2.1 Low Noise Amplifiers, and Amplifier Operation in the Presence of Jamming
With the explosive growth of wireless communications, the airwaves are rapidly being filled with signals of varying strengths and frequencies. Immunity to jamming has subsequently become a significant concern to any communication system. This is especially true for a mobile communication system, such as a cellular phone, as it is difficult to predict the jamming environment the system will be exposed to. At the same time, the need for portability, and thus long battery life, requires the system to consume as little power as possible.
In a typical wireless system, filtering before the low-noise amplifier can reject most jammers. However, a high rejection ratio incurs high insertion loss—a direct contributor of receiver sensitivity degradation. In addition, many close-in jammers are impossible to block given the size and cost restrictions of a mobile system. A number of different jammers including frequency modulation radio, television, navigational beacons, and microwave ovens will typically be detected by an omni-directional 2.5 GHz antenna. The low-noise amplifier, therefore, must have a large dynamic range: namely, a low noise figure and low intermodulation distortion. See S. Chen, “
Linearity Requirements for Digital Wireless Communi
-
cation,”
IEEE GaAs IC Symp. Dig., Anaheim, Calif., pp. 29-32, October 1997.
To meet these demands, the LNAs often consume the most power in a receiver; tradeoffs are usually required to balance dynamic range versus power consumption.
2. Power Detector
Power detector circuits are many and various, and are not commonly identified as requiring improvement. The low noise amplifier circuit of the present invention will show, however, that it is useful (but not necessary) to detect instantaneous amplifier output power, or (equivalently) voltage (into load), with two orders of magnitude (i.e., ×100) greater sensitivity that existing Schottky diode power detectors. To this end the present invention will be found to encompass a power detection circuit that is particularly characterized in that the power is not detected relative to ground, ergo an un-grounded power detection circuit. When a signal in which power is detected need not be sunk to, nor referenced relative to, ground, then it becomes possible to detect variations in the signal with much greater sensitivity.
SUMMARY OF THE INVENTION
The present invention contemplates a Low Noise Amplifier (LNA) that circumvents the compromise between (i) dynamic range and (ii) power consumption by optimizing power consumption for the operating environment. The LNA of the present invention exhibits a high dynamic range when it is near or in compression, but low power consumption when it is in small-signal operation where a large dynamic range is not necessary.
Furthermore, the dynamic range of the amplifier is extended: jamming may be countenanced without such distortion as would otherwise occur.
The present invention further contemplates an un-grounded a.c. signal power detection circuit that is very sensitive and very fast. This un-grounded power detection circuit will prove useful, even if not absolutely essential, in an s-band low-noise amplifier that is, in accordance with the present invention, improved for both power consumption and dynamic range, especially as both are required in a mobile environment.
1. A Method of Operating an Amplifier
In one of its aspects the present invention is embodied in a method of operating an amplifier where the amplifier—or, more exactly, the transistor components of the amplifier—has an load line. The amplifier is operated so as to emulate the property of a class AB amplifier where increasing amplifier input current raises the d.c. bias of the amplifier and increases amplifier output current. The amplifier is so operated nonetheless that it will never enter into class AB operation and will always operate in class A.
The method of operating an amplifier always in class A nonetheless to producing more output current from more input current includes two steps: 1) The amplified output of the class A amplifier is monitored; and, in response to detecting an increase in the amplifier output, 2) the load line of the amplifier is dynamically biasing to a higher d.c. bias point, causing the amplifier to consume more power and to produce a still larger amplified output signal. This “boosting” of the amplifier output could obviously cause a run-away condition, but this “boosting” is realized, in accordance with the present invention, so as to always maintain the amplifier to operate in class A.
The purpose of so operating a class A amplifier is demonstrated when the amplifier is used, inter alia, as an initial low-noise radio signal amplifier in a wireless communication system. In this environment an increase in amplifier output signal is indicative of a presence of a strong jammer component in the amplifier input signal. Moving the load line of the amplifier will cause the amplifier to draw more current, beneficially decreasing a noise figure while increasing gain of the amplifier. The amplifier will ultimately be caused to reach a new steady state with higher power and improved linearity. This improved response comes, of course, at the cost of increased power consumption,
Conversely, if no increase in amplifier output signal is detected then this is indicative that no strong jammer component is present within the amplifier input signal. In such a case neither the d.c. bias, nor the load line, will be raised, and the amplifier will operate quiescently, conserving power.
2. An Amplifier of Improved Dynamic Range
In another of its aspects, the present invention can be considered to be embodied in an amplifier of improved dynamic range.
The amplifier includes at least one Field Effect Transistor (FET) receiving at its gate an input signal from an external source, and amplifying this input signal in accordance with its drain-source bias voltage V
DS
to produce at its drain an amplified output signal.
A power detector circuit monitors the amplified output signal to produce a detected-power voltage signal V
DD
.
A dynamic bias control circuit compares the detected-power signal V
DD
to the drain-source bias voltage V
DS
so as to vary a gate-to-source voltage bias V
GS
of the input signal, actively moving a load line of the FET so as to cause the FET to consume more power when the amplified output signal becomes large.
The amplified output signal typically so becomes large because of a presence of a strong jammer component of the input signal. In this eventuality moving the load line of the at least one FET will cause the FET to draw more current, beneficially decreasing noise figure while increasing gain. Ultimately the amplifier of which the at least one FET forms a part to reach a new steady state with higher power and improved linearity.
However, when no strong jammer component of the input signal is present, and when the amplified output signal is correspondingly not large, then the FET, and the amplifier of which it forms a part, will remain biased in an operational condition where power is conserved.
Accordingly, the self-adjusting bias of the at least one FET results in both (i) improved power consumption and
Larson Lawrence
Xiong Wei
Greer Burns & Crain Ltd.
Rampuria Sharad
The Regents of the University of California
Trost William
LandOfFree
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