Telecommunications – Transmitter – With feedback of modulated output signal
Reexamination Certificate
1998-06-30
2001-01-09
Eisenzopf, Reinhard J. (Department: 2745)
Telecommunications
Transmitter
With feedback of modulated output signal
C455S127500, C455S115200, C455S553100, C455S522000
Reexamination Certificate
active
06173163
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of radio communications, and more particularly to transmitter power controls and methods for radio communications.
BACKGROUND OF THE INVENTION
Radiotelephone transmitters generally include an automatic gain control loop to maintain a desired transmission power level out of the antenna. Without such a gain control loop, the transmission power might vary as a function of factors such as transmission frequency, battery voltage, and/or temperature.
In particular, a portion of the power generated by the transmitter power amplifier can be coupled through a capacitor to a rectifier where it is converted to a voltage. This voltage can then be digitized and compared to a calibrated digital code at the radiotelephone microprocessor. A control signal from the microprocessor is used to adjust a variable gain amplifier when the digitized voltage is not equal to the calibrated digital code to maintain the desired transmission power.
Because a portion of the power generated by the transmitter is coupled through the feedback loop, however, the efficiency of the transmitter is reduced. Because the power amplifier generates more power than is actually transmitted through the antenna, the battery life may be reduced. A lower coupling capacitance may thus provide lower coupling and higher efficiency. Proper operation of the feedback loop, however, may dictate a certain level of coupling and the resulting inefficiency.
Moreover, a radiotelephone transmitter may operate at one of a plurality of transmission power levels depending on a signal strength desired at the time. For example, radiotelephones according to the IS-136 standard (IS-136 dual-mode dual band radiotelephones) may transmit at one of eight different transmission power levels ranging from 28 dBm to −4 dBm. Choosing a capacitance value for the coupling capacitor, however, may be difficult over this range of transmission power levels. In particular, a lower value coupling capacitance provides lower coupling and thus higher efficiency, but the lower capacitance may couple insufficient power at the lower power levels to maintain operation of the feedback loop. Higher capacitor values may provide sufficient power coupling at lower power levels for operation of the feedback loop, but the reduced efficiency may significantly reduce the radiotelephone battery life.
U.S. Pat. No. 5,363,071 to Schwent et al. discusses a method for varying coupling of a radio frequency signal. This is accomplished by selecting between a first operating mode of the RF coupler having strong coupling, responsive to a first predetermined power level, such that the RF coupler produces a first coupled RF signal responsive to the RF signal and a second operating mode of the RF coupler having weak coupling, responsive to a second predetermined power level, such that the RF coupler produces a second coupled RF signal responsive to the RF signal. The strongly and weakly coupled RF signals, however, may still contribute to undesired transmission inefficiencies.
Furthermore, it may be difficult to provide a cost effective analog-to-digital converter having useful resolution over the range of power levels discussed above. For example, a 32 dB range of output powers may be difficult to measure using a conventional 8 bit analog-to-digital converter. In conventional arrangements, the highest code of the analog-to-digital converter is set at the maximum operating voltage of the converter, and the lowest code is set at ground. Accordingly, there is a voltage range near the supply voltage and ground where the digital code is variable or redundant. For example, if the supply voltage is 3.3V and there is a 300 mV range of uncertainty, the analog-to-digital converter may only be able to reliably convert from 0.3V to 3V providing a dynamic range of:
|x
|=20 log(0.3/3)=20 dB.
For the reasons discussed above, it may be difficult to provide useful feedback at lower power levels. Accordingly, radiotelephones may effectively provide open loop transmit operations at the lower power levels thereby reducing performance thereof. Furthermore, known feedback loops may result in undesired transmission inefficiencies.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved transmission systems and methods for radio communications devices.
It is another object of the present invention to provide transmission systems and methods having improved efficiency for radio communications devices.
It is still another object of the present invention to provide transmission systems and methods having improved power control feedback loop operation.
These and other objects are provided according to the present invention by coupling a portion of the transmitted power during spaced apart intervals of time and blocking coupling of the portion of the transmitted power between the spaced apart intervals of time. In other words, the transmission power is sampled so that a portion of the transmitted power is coupled into the feedback loop only during the sampling intervals. By not coupling transmission power into the feedback loop outside the sampling intervals, a greater portion of the transmitter power reaches the antenna thus improving the transmitter efficiency thereby increasing battery life.
According to an embodiment of the present invention, a radio communications device can include a transmitter, a switch, and a measuring circuit wherein the transmitter transmits radio communications at a transmitted power. The switch couples a portion of the transmitted power during spaced apart intervals of time and blocks coupling of the portion of the transmitted power between the spaced apart intervals of time. The measuring circuit measures the coupled portion of the transmitted power during the spaced apart intervals of time. Accordingly, a feedback circuit can maintain the transmitted power at a desired level responsive to the coupled portion of the transmitted power measured by the measuring circuit. By blocking coupling between the spaced apart intervals of time, the efficiency of the transmitter can be increased.
The transmitted power is preferably selected from one of a plurality of predetermined power levels. In addition, the measuring circuit can include first and second attenuating circuits, and a multiplexer. The first and second attenuating circuits provide respective first and second samples of the coupled portion of the transmitted power at respective first and second levels of attenuation. The multiplexer multiplexes the first sample of the coupled portion of the transmitted power for a first range of the predetermined power levels and the multiplexer multiplexes the second sample of the coupled portion of the transmitted power for a second range of the predetermined power levels. Accordingly, a single analog-to-digital converter can be used to measure the full range of power levels with improved dynamic range. In essence, the attenuating circuits scale the first and second ranges of power levels so that each of the first and second ranges of power levels can be measured using the full dynamic range of the single analog-to-digital converter.
The first and second attenuating circuits can include respective first and second voltage dividers. In particular, the first voltage divider can be coupled between the switch and a reference voltage, and the second voltage divider can be coupled between an output node of the first voltage divider and the reference voltage. Accordingly, the first voltage divider provides a first level of attenuation, and the second voltage divider provides a second level of attenuation greater than the first level of attenuation.
The spaced apart intervals of time preferably occur for a duration and at a rate so that transmission noise is reduced. Each of the spaced apart intervals of time is thus preferably less that 5 ms. Furthermore, the portion of the transmitted power is preferably coupled at a frequency in a range outside an audio range of th
Eisenzopf Reinhard J.
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Nguyen Duc
LandOfFree
Switched sampling systems and methods for monitoring radio... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switched sampling systems and methods for monitoring radio..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switched sampling systems and methods for monitoring radio... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2458189