Telecommunications – Transmitter – Measuring – testing – or monitoring of transmitter
Reexamination Certificate
1998-09-14
2002-08-06
Trost, William (Department: 2683)
Telecommunications
Transmitter
Measuring, testing, or monitoring of transmitter
C455S126000, C455S522000, C455S117000, C455S127500, C455S234200, C330S129000, C330S285000
Reexamination Certificate
active
06430402
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to power amplifier control circuits. More specifically, the invention relates to saturation detection and control for power amplifiers.
BACKGROUND OF THE INVENTION
The use of power amplifiers in transmitting radio frequency (RF) signals has many applications, including, but not limited to radiotelephone communications systems. A typical radiotelephone communications system includes multiple fixed site transceivers. Each fixed site transceiver is an interface between the line telephone system and multiple portable, or mobile radiotelephone units located within a geographic area served by the fixed site transceiver. The fixed site transceiver and the radiotelephones communicate by sending radio frequency (RF) signals to each other.
Radiotelephones are generally of two different types. Some conventional radiotelephone systems employ analog units that are basically the equivalent of a walkie-talkie. Each analog unit communicates voice messages by broadcasting a radio frequency (RF) carrier signal which has been modulated in some fashion by an analog signal corresponding to the voice message. Other radiotelephone systems employ a digital unit. Digital units convert the speech into a digital representation and then broadcast a radio frequency (RF) carrier modulated with the digital representation of the speech.
Analog radiotelephone systems typically employ a limited RF spectrum for radiotelephone communications. According to one conventional communication method, the RF spectrum is divided into relatively narrow segments of frequency. Upon request, each radiotelephone is allotted one of these dedicated segments in which to broadcast and receive signals from the fixed site transceiver. This method of communication is known as Frequency Division Multiple Access (FDMA). Using this method the radiotelephone transmitter would turn on and remain on the fixed frequency for the duration of the call. If the turn on functions and turn off of the transmitter are limited to the beginning and end of the phone call, the turn on and turn off function's timing requirements are not very stringent.
There are several difficulties with the described FDMA system however. One of the difficulties is that, in portable units, keeping the transmitter powered during the course of a telephone call can consume a significant amount of energy. Since operation time is limited by the amount of energy contained within the portable unit, it is typically desirable to minimize power consumption and thereby increase the portable unit's operating time.
Another problem with the analog version of the FDMA system is that, because it is an analog system, it is prone to the usual problems inherent in analog systems such as spurious signals, interferences from other sources of RF energy, multipath reception, and fade outs. The same types of problems will occur with digital systems, but because they are digital, error correction coding and a variety of other digital and software techniques help compensate for these difficulties. Digital systems can help to more efficiency use precious bandwidth providing more users than analog systems for a given level of quality. Accordingly, alternate methods of communication have been developed such as Time Division Multiple Access (TDMA). This method operates by sharing a single frequency band among users by dividing the band into time slots and allotting a time slot to each radiotelephone unit. Each radiotelephone unit then broadcasts data during its allotted time slot and stops transmission until the next time allotted time slot occurs, and then the radiotelephone unit broadcasts again. This method has advantages which address many of these aforementioned analog FDMA problems.
First, because the radiotelephone is actually broadcasting only during it's own time slot, there is a reduction in the power consumed because there is no need to keep the RF power amplifier of the transmitter on continuously during the call. In fact if the RF power amplifier of the transmitter did remain on during the entire call it may result in interference with other units using successive time slots. The RF power amplifier in a mobile radiotelephone usually requires a relatively large amount of energy and is therefore a significant contributor to battery drain. Because in TDMA systems the power amplifier of the transmitter is actually turned off most of the time a significant saving in terms of energy consumption can be realized.
Second because continuous speech is being transmitted, and only time slots are available for broadcast, it is convenient to represent TDMA signals in digital format. The speech must be encoded into discrete portions to fit in time slots in such a way that continuous speech can be recreated at the receiving end. Because TDMA is digital, further techniques such as digital data compression and various digital coding techniques may be used to minimize transmission errors.
The use of TDMA, however, can bring a new set of constraints. One of these constraints involve the requirement of transmitter control for limiting transmissions to the allotted time slots only. This type of transmission, often called burst or pulse transmission mode, involves turning on the RF power amplifier just after the beginning of a time slot allotted to the radiotelephone unit, increasing the power to a predetermined level, transmitting the encoded signals during the time slot, decreasing the power, and finally shutting off the RF power amplifier near the end of the time slot. One of the problems inherent in such a mode of transmission is the possibility of spurious RF radiation that can be created if the RF power amplifier, or any solid state device, is turned on or shut off too quickly, or in a non linear fashion.
A second problem is the tendency for a pulsed radio to disturb neighboring frequency channels, a phenomenon often called AM splash. AM splash generally occurs when a power amplifier ramps up too fast causing energy to appear outside the allotted transmission bandwidth.
A third problem can occur when an RF power amplifier does not turn off prior to the end of the allotted time slot thereby disturbing the transmission on the succeeding time slot. All these problems are heightened by the fact that a pulsed transmission system turns on and off many times per second and so any interference generated tends to happen repeatedly and continuously during the time the interfering system is activated.
To combat these problems standards have been developed regarding burst mode radiotelephone transmission. On of the most popular standards is the Global System for Mobile Communications (GSM) format. The GSM format is the basis for the European Personal Communications Standard (PCS) and has also found wide acceptance in North America as the PCS-1900 standard. In order to insure that the aforementioned problems are minimized the GSM format includes a power versus time templates that specify power limits for broadcasting in a burst mode in such a way as to minimize unwanted interference. This template specifies the desired power output level ranges versus time for a TDMA time slot. The GSM power template dictates a maximum and minimum power level for each point on the curve. It is desirable to limit the power output to values inside the GSM power template, to control the desired level for transmission. It is also desirable to have a smooth turn on and turn off of the RF amplifier, to minimize the possibility of spurious RF generation. Many radiotelephone systems implement the GSM standard by controlling the RF power amplifier in such a manner that it remains within this template.
In an analog control system a comparator compares a desired level of a preset variable, called a setpoint or reference signal, with the value of the variable the control system is attempting to control. The comparator generates an error signal which represents the difference between the desired setpoint, and the actual value of the variable that the control system is attempting to con
Conexant Systems Inc.
Foley & Lardner
Perez-Gutierrez Rafael
Trost William
LandOfFree
Power amplifier saturation prevention method, apparatus, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power amplifier saturation prevention method, apparatus, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power amplifier saturation prevention method, apparatus, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2936203