Telecommunications – Transmitter – Power control – power supply – or bias voltage supply
Reexamination Certificate
1998-12-31
2001-01-23
To, Doris H. (Department: 2745)
Telecommunications
Transmitter
Power control, power supply, or bias voltage supply
C455S091000, C455S073000, C330S278000, C330S285000, C330S127000
Reexamination Certificate
active
06178313
ABSTRACT:
The present invention describes a control method for both power amplifier (PA) gain and power consumption. More particularly, the present invention describes how this control is accomplished by the bias current applied to the power amplifier. Incremental adjustment of the bias current level applied to the power amplifier causes a corresponding incremental change in the gain of the power amplifier. And, the bias current of the power amplifier can be selected to be no higher than necessary, thereby minimizing power consumption of the transmitter.
BACKGROUND OF THE INVENTION
Wireless communication systems have become widely popular in recent years. Advancements in communication technology have permitted the development, and popular usage, of new types of communication devices, of improved performance, portability, and affordability.
In a wireless communication system, a radio communication channel extends between a sending station and a receiving station. The radio channel is defined upon a portion of the electromagnetic spectrum. This communication link between the sending and receiving stations is wireless and can thereby be untethered.
A cellular communication system is exemplary of a wireless, multi-user communication system. Here, several fixed-site base stations are installed to cover a geographical area. By transmitting signals with controlled power, the same frequencies can be re-used at different locations throughout the geographical area. Thereby, communication capacity is maximized power control is at the core of cellular system design.
Various standards have been developed for cellular communication systems. Interim Standard IS-95, promulgated by the EIA/TIA, is exemplary of a standard which pertains to a cellular communication system utilizing CDMA (code-division, multiple access) communication techniques. In a CDMA communication system, several communication signals share a common frequency channel. In such a communication scheme, the power levels of each user must be regulated to achieve optimal capacity. Power control is needed to ensure that none of the signals overwhelm the other signals.
Power control is used to ensure that transmitted communication signals are strong enough to recover the informational content at the receiver, but also low enough to not reduce the communication capacity of the communication channel. Most communications systems utilize closed-loop power control schemes. In the closed-loop power control scheme defined in the IS-95 standard, power control bits are generated and transmitted by network infrastructure on the forward link channel to a radio telephone. These power control bits control the power levels for the reverse link communication signals transmitted by the radio telephone. Therefore, a method is needed to change the power level of the transmitter. Several technical challenges are presented by the power control bit rate and the accuracy requirements of IS95.
Most radio telephones are powered by portable power supplies or batteries. These batteries store limited energy, and therefore need to be replaced or recharged regularly. It is also advantageous to minimize the power requirements of the radio telephone. By reducing the power required to operate the radio telephone, the discharge rate for the stored energy of a battery pack is reduced. Thereby the time period during which a single battery pack can be utilized to power the radio telephone can be increased. That is to say, a technical challenge exists to provide manners by which to increase the “talk time” of the radio telephone with a single battery pack.
The transmitter portion of a radio telephone typically includes a power amplifier. The power amplifier amplifies a reverse link signal prior to its transmission so that it will be received by a base station via a radio channel. A power amplifier requires relatively large amounts of energy for its operation. Conventionally, power amplifiers are powered or biased to accommodate the maximum power levels transmitted by the radio telephone. However, in an IS-95, the typical power levels of reverse link signals are generally significantly less than the maximum power levels.
A manner to provide control of gain and power consumption in a power amplifier is advantageous.
A manner by which to utilize the power amplifier to effectuate power control in a two-way power control scheme is also advantageous.
It is in light of this background information related to transmitter circuits, that the significant improvements of the present invention have evolved.
SUMMARY OF THE INVENTION
The present invention advantageously provides a method to control the gain and power consumption of a power amplifier using its bias current.
In one aspect of the present invention, advantage is taken of the relationship between the level of gain exhibited by the power amplifier and the level of bias current applied to the amplifier. By increasing the level of bias current applied to the power amplifier, a corresponding increase in the gain of the power amplifier is exhibited. Analogously, a decrease in the level of bias current applied to the power amplifier causes a corresponding decrease in the level of gain exhibited by the power amplifier.
In one implementation, gain control is directed by closed loop information in the form of power control bits. Those power control bits are received by the radio telephone. In response to the received commands, a gain controller alters the level of bias current applied to the power amplifier. The power amplifier forms a portion of the transmitter portion of the two-way transceiver and the gain of the power amplifier is determined in part by the desired transmit power level.
In another implementation, the power lever transmitted is controlled by the gain of a variable gain amplifier (VGA) and a power amplifier. The power control commands are provided to a gain controller. The gain controller, in turn, adjusts the level of amplification of the variable gain amplifier and also the level of bias current applied to the power amplifier. The combination of commands issued by the gain controller direct the signals generated by the transmitter to be of desired power levels.
In one embodiment of the present invention, the gain controller includes a memory element with values of bias current and the corresponding levels of PA gain. The desired PA gain is first determined. From this, the corresponding bias current read from memory and applied to the PA. In an embodiment in which gain control is jointly controlled by a power amplifier and a variable gain amplifier, the memory element is capable of storing additional information related to the variable gain amplifier.
Reduction in the gain of the power amplifier so that the transmitted power level just adequately forms the radio link ensures battery energy is not wasted and interference is minimal.
The power amplifier has an input terminal where the communication signal is applied and an output terminal where the amplifier communication signal is generated. The power amplifier amplifies the communications signal at a level selected by the bias current, generated by the gain controller.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.
REFERENCES:
patent: 5287555 (1994-02-01), Wilson et al.
patent: 5432473 (1995-07-01), Mattila et al.
patent: 5493707 (1996-02-01), Kamitani
patent: 5640691 (1997-06-01), Davis et al.
patent: 5926749 (1999-07-01), Igarashi et al.
Groe John B.
Mages Phil
Holland & Hart LLP
Kelly Robert H.
Nokia Mobile Phones Limited
To Doris H.
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