Telecommunications – Receiver or analog modulated signal frequency converter – With particular receiver circuit
Reexamination Certificate
1998-09-16
2002-07-09
Chin, Vivian (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
With particular receiver circuit
C455S127500, C455S561000
Reexamination Certificate
active
06418304
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to wireless communications. More particularly, the invention relates to a method and apparatus for improving efficiency of a high power linear amplifier employed in a base station of a wireless communications system.
Base stations of contemporary wireless communications systems (e.g., cellular telephone systems) typically employ a number of high power linear amplifiers to amplify information signals destined for wireless communication terminals (e.g., cellular telephones, personal communication devices, etc.) For instance, in frequency division multiple access (FDMA) systems, each high power amplifier usually amplifies a multi-carrier signal, with each carrier modulated with voice and data information destined for a particular wireless terminal. The communication channel associated with each carrier is narrowband, typically about 25-30 KHz wide. Hence, the high power amplifier must be highly linear to avoid generating intermodulation distortion (IMD) products that will introduce noise into adjacent communication channels. Whether the modulation technique is analog, e.g., FM, or digital, such as in time division multiplexed (TDM) systems employing phase shift keying (PSK), amplifier linearity is important to system performance. Similarly, in code division multiple access (CDMA) systems, in which many information signals are coded and transmitted over a common, wider communication channel of about 1.2 MHz, linear amplification in the high power stage is required for optimum performance.
Unfortunately, efficiency of the base station amplifier is inversely related to its linearity. To achieve a high degree of linearity, the amplifiers are biased to operate in the class A or “slight” class AB (meaning class AB operation that is closer to class A than to class B). Maximum AC to DC efficiency achievable for class A operation is 50%, whereas that of a class AB amplifier is between 50 and 78.5% (the latter representing the maximum efficiency of a class B amplifier). The closer the particular class AB operation is to class A, the lower the maximum efficiency. For amplifiers employing field effect transistors, the class of operation is set in accordance with the gate voltage applied, which controls the quiescent (idle) drain current. For class A operation, the gate voltage is set so that the idle drain current is approximately in the middle of the range between pinch-off and saturation. Class B amplifiers are biased near pinch-off, resulting in a rectified drain current waveform. Class AB amplifiers are biased in between the bias points of classes A and B.
Typically, strict linearity requirements in modern wireless communication systems dictate the use of the relatively inefficient class A or slight class AB modes. As a result, significant DC power is dissipated by the amplifiers, thereby generating heat which must be controlled to avoid degrading amplifier performance and reliability. Hence, the use of elaborate heat sinks and fans become a necessary by-product of the high linearity system. Naturally, these measures add to the cost, size and weight of the base station equipment. As the number of wireless communications users continues to grow, so do the number of base stations and the need to keep them small, light and inexpensive. Thus, a great deal of research has focused on the quest to improve amplifier efficiency in these and other systems.
SUMMARY OF THE DISCLOSURE
The present disclosure pertains to a method and apparatus for improving thermal efficiency and reliability of a linear power amplifier of a communication system. In an illustrative embodiment, the communication system operates in a half-duplex mode in which information signals are transmitted and received in alternating time intervals. A transistor control terminal (e.g., gate) of the amplifier is biased at a first bias voltage during transmit intervals of the half-duplex mode, and at a second bias voltage different from the first bias voltage during receive intervals of the half-duplex mode. The second bias voltage is sufficient to reduce idle currents in the amplifier during the receive intervals, thereby improving thermal efficiency of the amplifier.
Also disclosed is a base station including a base station controller, a variable bias control circuit and a linear power amplifier. The variable bias control circuit operates under the control of the base station controller to supply a variable bias voltage to the amplifier. Thermal efficiency of the amplifier is improved by reducing idle currents via appropriate bias voltage control during a weak signal transmitting mode and/or during receive intervals of a half-duplex operating mode.
REFERENCES:
patent: 4439744 (1984-03-01), Kumar et al.
patent: 4748423 (1988-05-01), Jinich
patent: 5278517 (1994-01-01), Fujita
patent: 5426641 (1995-06-01), Afrashteh et al.
patent: 5568094 (1996-10-01), Bowen et al.
patent: 5669068 (1997-09-01), Kielmeyer et al.
patent: 5712593 (1998-01-01), Buer et al.
patent: 5724005 (1998-03-01), Chen et al.
patent: 5793757 (1998-08-01), Uddenfeldt
patent: 5831477 (1998-11-01), Tsumura
patent: 6043712 (2000-03-01), Leizerovich et al.
patent: 6122488 (2000-09-01), Leizerovich et al.
patent: 6215358 (2001-04-01), Hon et al.
patent: 6215987 (2001-04-01), Fujita
patent: 6223056 (2001-04-01), Appel
patent: 6298221 (2001-10-01), Nguyen
patent: 0 837 559 (1998-04-01), None
patent: WO 97/41642 (1997-11-01), None
Esmailzadeh et al. Time Division Duplex CDMA Communications, IEEE Personal Communications, 1997.*
European Search Report—Dated Dec. 17, 1999.
New RF ICs and Modules Boost Market Development, RF Design. Apr. 17, 1994, No. 4, Atlanta, GA.
Miniaturized, X-Band Solid-State Transmitter, Published Jun. 14, 1993, 1993 IEEE MTT-S Digest.
Appiah Charles N.
Chin Vivian
Dilworth & Barrese
Lucent Technologies - Inc.
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