Amplifiers – With semiconductor amplifying device – Including protection means
Reexamination Certificate
1999-05-10
2001-03-06
Shingleton, Michael B. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including protection means
C330S20700P, C327S051000, C327S081000, C257S382000
Reexamination Certificate
active
06198351
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to power sensing devices, and more particularly to a power sensor circuit comprising a field effect transistor sensor which is coupled to a power amplifier for sensing the output power of the amplifier.
BACKGROUND OF THE INVENTION
Current power sensing devices often take the form of a shunt diode, which is tapped off of an interstage matching network of a power amplifier. An example of a device of this type is provided in FIG.
1
. Such a diode rectifies a voltage wave, which is proportional to the output power of the total amplifier. This yields a DC voltage that is a non-linear function of the transmitted output power from the power amplifier. A relationship between the DC voltage output from the diode rectifier, and the output power of the power amplifier may be established using well-known methods. It is also known in the art that the detection of output power of a power amplifier may be accomplished by the use of a forward directional coupler, which is coupled to a diode detector at the output of the amplifier. The diode detector operates to detect and rectify a power wave proportional to the output power of the power amplifier. Such a device is illustrated in FIGS.
2
and
3
A-B. A number of problems, however, exist with each of the above devices.
First, the use of an internal diode detector requires that it be by-passed using a large value capacitor, as well as low pass filter, for holding the diode rectified voltage which is a function of the incident power onto the diode detector. Such a circuit requires a relatively large area semiconductor (for example, a large area of gallium arsenide) in order to properly implement such a circuit. Furthermore, the use of an output forward directional coupler to sample and rectify the output power of the power amplifier results in an additional expense associated with the circuit. Moreover, the use of an ouput forward directional coupler also requires a temperature compensated diode detector circuit, resulting in additional cost and complexity to the sensing circuit.
Accordingly, a device which replaces each of the above components and which utilizes a single semiconductor structure that is both small and compact is highly desirable.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power amplifier comprising a plurality of cascaded field effect transitors (FETs), a power sensing circuit for sensing the output power of the power amplifier comprising a FET device operative in a first linear mode and second saturated mode of operation, the FET having source, gate and drain electrodes; and a resistor connected between the source electrode and a reference potential for generating a voltage drop between the source and the reference potential such that when the FET operates in the saturation mode, the voltage drop is indicative of the output power of the power amplifier.
It is also an object of the present invention to provide a power sensing circuit for sensing the ouput power of a semiconductor device comprising a plurality of semiconductor FETs which are driven via an input signal from linear to power saturated conditions, wherein a plurality of drain finger electrodes, source finger electrodes, and gate finger electrodes define each of the semiconductor FETs and wherein the source finger electrodes are coupled to a reference potential, the power sensing circuit comprising a FET having a source, gate and drain electrode disposed on the semiconductor substrate wherein the source electrode corresponding to the sensing circuit FET is connected to the reference potential via a bond pad and a resistor, such that when the power amplifier enters a saturated condition, the power sensing circuit FET enters saturation and a voltage drop is generated across the resistor indicative of the level of saturation of the power sensing circuit FET and which corresponds to the output power of the amplifier.
It is a further object of the present invention to provide a method for providing a power sensing apparatus for a power amplifier comprising the steps of forming an active region at a surface of a semiconductor substrate forming a plurality of drain finger electrodes, source finger electrodes, and gate finger electrodes within the active region; forming a source bus for connecting each of the source finger electrodes and coupling the source fingers to a reference potential; and removing one of the FET source finger connections and inserting a resistor between the source finger electrode and the reference potential, wherein when the power amplifier enters compression mode the FET having the source finger coupled to the resistor operates to generate a voltage across the resistor representative of the output power of the amplifier.
REFERENCES:
patent: 5013935 (1991-05-01), Mahabadi
patent: 5426395 (1995-06-01), Cygan
Buchanan & Ingersoll PC
Plevy Arthur L.
Shingleton Michael B.
Tyco Electronics Logistics AG
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