Telecommunications – Transmitter – With feedback of modulated output signal
Reexamination Certificate
1998-08-31
2001-11-20
Hunter, Daniel (Department: 2684)
Telecommunications
Transmitter
With feedback of modulated output signal
C455S091000
Reexamination Certificate
active
06321072
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to function generators, and more particularly to a flexible transfer function generator.
2. Related Art
Power amplifiers are commonly used in a number of contemporary devices, including, for example, wireless communication devices such as handsets and basestations. In such devices, the power amplifier amplifies the modulated signal to a desired level such that the radiated power from the device's antenna is of sufficient strength to fall within the dynamic range of the intended receiver.
In many applications, closed loop systems are used to control radiated power to within a relatively narrow range. Closed loop systems typically accomplish this goal through the use of a feedback loop. Such feedback loops can include, for example, a power sensor at or near the antenna to detect the actual transmitted power level. The detected power level can be compared with a desired power level to determine a difference between actual and desired power levels. This difference, often represented as a voltage level, is integrated and fed back to the power amplifier to control the output of the power amplifier.
One drawback of contemporary closed-loop systems is that the power amplifier typically has a non-linear transfer function. As such, the response of the overall system, even with the feedback loop, is non-linear. This can result in less-than-desirable response characteristics of the feedback loop. For example, if the loop is operating in a region where there is too little gain, loop response may be slower than desired. If on the other hand, the loop is operating in a region where there is too much gain, the system may go into oscillation.
In some applications, the problem is more prevalent because the power amplifier tends to primarily operate in the non-linear region. For example, in devices such as wireless devices operating according to the GSM standard, the supply voltages tend to be very low and the output power is typically quite high. As such, in this type of application, the power amplifier often operates in the saturation region. As a result, the transfer function of the power amplifier exhibits the above-described non-linear characteristics.
SUMMARY OF THE INVENTION
The present invention provides a system and method for implementing a flexible transfer function generator for a variety of applications. According to one embodiment of the invention, the transfer function generator includes both linear and non-linear function generators to allow the transfer function generator to compensate for non-linearities elsewhere in the implemented system.
In one application, the transfer function generator is provided as a prescaler in a feedback control loop to compensate for non-linearities in the controlled system. The transfer function generator can include tuning components to allow the transfer function generator to be optimized for implementation in a variety of alternative applications, or with a variety of alternative components in a given application.
Specifically, in one embodiment, the transfer function generator includes a tuning device that controls the threshold level at which the non-linear function generator turns-on. In embodiments in which the transfer function generator is implemented to operate on current, the tuning device can be implemented as a resistance that shunts a portion of the input current to ground. In this embodiment, when the input current is greater than the amount shunted to ground, non-linear function generator turns on and provides an output which is a non-linear function of the input current.
Likewise, a tuning device can be implemented to adjust the output of the linear function generator. Similarly, in embodiments operating on current, the tuning device controls the amount of current shunted to ground, thereby controlling the output level of the linear function generator.
In embodiments using both linear and non-linear function generators, the respective outputs of the linear and non-linear function generators can be summed to provide a composite output that responds in such a manner as to provide the transfer function generator with both a linear and a non-linear region. The tuning devices can be used to adjust the characteristics of the response curve of the transfer function generator, including the point at which the response becomes non-linear.
According to one aspect of the invention, the transfer function generator can be implemented in a wireless communication device, such as, for example a device configured to operate according to the GSM standard or other communication protocol or standard. The communication device can include, for example, a power amplifier configured to amplify a signal for transmission by an antenna over a communications channel; a power level sensor configured to sense the power level radiated from the antenna; a comparator configured to compare a difference between the power level sensed by the power level sensor and the desired output power level and to provide a voltage level output indicating the difference; and an integrator configured to integrate the voltage level output from the comparator to provide a voltage level indicating an error level. The transfer function generator can include a non-linear function generator configured to provide an output current that is a non-linear function of an input current representing the voltage output from the integrator, and a linear function generator configure to provide a linear output current as a function of an input current representing the voltage output from the integrator, and a summing junction configured to combine the non-linear output current with the linear output current; wherein the transfer function generator provides a non-linear response to the error signal generated by the integrator to compensate for non-linearity introduced elsewhere in the communication system. The wireless communication system can also include a voltage to current converter, configured to convert the output voltage of the integrator into a current; and a current to voltage converter configured to convert the current output from the transfer function generator to a voltage level and to provide the voltage level to control pins of the power amplifier.
The transfer function generator can further include a first tuning device to control the amount of current needed to turn on the non-linear function generator; and a second tuning device to control the output level of the linear function generator; wherein the first and second tuning devices are variable resistors.
Further features and advantages of the invention as well as the structure and operation of various embodiments of the invention are described in detail below with reference to the accompanying drawings.
REFERENCES:
patent: 5334945 (1994-08-01), Yokoya
patent: 5511239 (1996-04-01), Dennerlein
patent: 5548826 (1996-08-01), Sayers
patent: 5697074 (1997-12-01), Makikallio
patent: 5884150 (1999-03-01), Sugawara
patent: 5977833 (1999-11-01), Attimont
patent: 6141390 (2000-10-01), Cova
Carpineto Lorenzo
Cipriani Stefano
Takeshian Anthony A.
Conexant Systems Inc.
Corsaro Nick
Howrey Simon Arnold & White , LLP
Hunter Daniel
LandOfFree
Distortion control feedback loop utilizing a non-linear... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Distortion control feedback loop utilizing a non-linear..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Distortion control feedback loop utilizing a non-linear... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2613346