Amplifiers – With semiconductor amplifying device – Including field effect transistor
Patent
1993-02-25
1994-12-13
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including field effect transistor
330285, 330297, H03F 316
Patent
active
053732502
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns transistor power amplifiers or SSPA (Solid-State Power Amplifiers) and in particular amplifiers using MESFET (MEtal-Semiconductor Field-Effect Transistor) power devices.
2. Description of the Prior Art
These amplifiers are used in space applications i.e. satellites for the final radio frequency amplification stages especially for microwave signals, for example the signals driving a travelling wave tube (TWT) designed to transmit a highpower communication signal. Such amplifiers are particularly advantageous in this field because of their high intrinsic reliability, their low mass, their compact dimensions and the ease with which they can be adapted to different applications. MESFET are virtually universally used to amplify signals at frequencies above 1.5 GHz.
The amplifiers operate in one of two modes, depending on how sensitive the signals to be amplified are to non-linearities of the amplifier which themselves generate distortion.
In the first or linear mode, which must be used to amplify signals which are particularly sensitive to such non-linearities such as multiple carrier signals, the operating point of the amplifier is adjusted so that the amplifier always operates below its rated power output so that there is a safety margin and very little distortion from the input to the output.
In the second mode, which can be used to amplify signals which are less sensitive to non-linearities such as QPSK (Quadrature Phase Shift Keying) signals on a single carrier, the safety margin referred to above is dispensed with which significantly increases the output power of the amplifier but however also increases distortion. This mode is sometimes called "saturation" mode.
In either case the operating temperature of the amplifier significantly effects its characteristics. This is particularly critical in space applications given the very wide range of temperature variation routinely encountered: the case of amplifiers on board satellites, for example, the temperature of the transistors typically varies between -10.degree. C. and +40.degree. C., with frequent and relatively sudden heating/cooling cycles.
An increase in temperature reduces drift mobility and the maximum drift speed of the electrons in the MESFET channel, so reducing the transconductance of the component and the maximum channel current. Thus as the temperature increases the gain and the output power of the amplifier are reduced. At low temperatures, on the other hand, the contrary effect on the gain and the output power leads to excessive power consumption by the amplifier.
Techniques for compensating these temperature effects have already been proposed.
To be more precise, in a first family of known techniques the gain of the amplifier is compensated globally by operating on a pre-amplifier stage on the input side of the power amplifier. The pre-amplifier stage includes a circuit whose gain varies as a function of temperature in the opposite direction to the variation in the gain of the other circuits of the amplifier so as to compensate the overall gain of the latter. The variable gain circuit may be a variable attenuator or a variable gain amplifier controlled by a component responsive to temperature or an automatic gain control circuit controlled by a circuit measuring the output power of the amplifier (by means of a coupler, for example) and adjusting the gain of the pre-amplifier stage to maintain a constant output level and therefore a constant overall gain of the amplifier system.
However it is implemented, this technique is effective in the field of linear operation but becomes ineffective at saturation because of the insufficient dependency of output power on input power: when the amplifier saturates, variation of the level at the output of the pre-amplifier stage varies the output power only slightly.
A method of this kind is thus unable to compensate correctly for the effect of temperature variations on an amplifier operating in saturation mode.
Another k
REFERENCES:
patent: 4438411 (1984-03-01), Rubin et al.
patent: 4849710 (1989-07-01), Vo
Temperature Compensation for Microwave GaAs FET Amplifiers, Lamberto Faffaelli and Rober Goldwasser, Microwave Journal, vol. 29, No. 5, May 1986, pp. 315-316, 318, 320, 321.
Review of Scientific Instruments, vol. 42, No. 5, Mai 1971, New York US pp. 714-715, M. K. Kopp, Wide Band Low Noise Voltage Sensitive Preamplifier with Temperature Compensation.
Battisti Alberto
Denti Ferruccio
Gatti Giuliano
Agence Spatiale Europeenne
Mullins James B.
LandOfFree
MESFET power amplifier and its power supply unit, in particular does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with MESFET power amplifier and its power supply unit, in particular , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and MESFET power amplifier and its power supply unit, in particular will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1195682