Amplifiers – Combined with automatic amplifier disabling switch means
Reexamination Certificate
2002-07-09
2004-10-19
Nguyen, Long (Department: 2816)
Amplifiers
Combined with automatic amplifier disabling switch means
C330S129000, C330S302000, C330S306000
Reexamination Certificate
active
06806767
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of power amplifiers in multi-band communication systems. More particularly, the present invention relates to circuitry associated with such power amplifiers, such as harmonic filters, impedance load switching circuits, pre-distortion phase filters, and the like.
BACKGROUND OF INVENTION
In the United States, cellular operating licenses have been awarded by the Federal Communication Commission (FCC) pursuant to a licensing scheme which divides the country into geographic service markets. Cellular licenses were originally granted for radio frequency (RF) blocks in the 800 MHz range. Most 800 MHz cellular telephone systems in the United States utilize the Advanced Mobile Phone Service (AMPS) analog air interface standard. A later generation air interface standard for the 800 MHz band, known as D-AMPS, has subsequently been developed and implemented. The D-AMPS standard comprises both digital and analog cellular communication. Thus, there are presently both analog (AMPS) and digital (D-AMPS) cellular telephone networks in operation at 800 MHz in the United States.
In response to increased demand for cellular services, a number of digital air interface standards were developed for providing efficient digital communication of voice, data, fax and text messages under the umbrella of “personal communications services” or PCS. Operational PCS systems, such as systems based on the GSM TDMA (Time Division Multiple Access) or IS-95 CDMA (Code Division Multiplex Access) air interface standards, are being implemented in the United States in the 1900 MHz frequency range. Meanwhile, existing 800 MHz cellular systems continue to operate. Thus, there are presently operating in the United States analog and digital cellular systems at 800 MHz and digital PCS systems at 1900 MHz. Mobile subscribers who desire to receive services from systems operating at 800 MHz and from systems operating at 1900 MHz must either use two different mobile transceivers or use a single “dual-band” mobile transceiver which can receive and transmit radio frequency (RF) signals in both frequency bands.
Power control is essential to the smooth operation of CDMA communication systems. Since there are many users sharing the frequency spectrum, in order to resolve the near-far multiple-access in a spread-spectrum system, output power for each individual user needs to be adjusted dynamically to maximize the system capacity. For this reason, a typical CDMA handset is operated under a varied output condition. According to actual statistics obtained from the field, a CDMA cellular phone handset spent approximately 95% of its time transmitting output power in a range of 10-30 dB lower than its maximum rated output power. Recognizing this fact, most CDMA handset power amplifiers have lower power (LP) and high power (HP) modes of operation. The purpose of this two-mode operation is to improve the efficiency performance at the LP mode.
FIG. 1
shows a diagram of a typical wireless voice communication device
100
, such as a mobile phone handset
100
for cellular telephone use. For the voice interface, device
100
includes a microphone
102
for converting audio signals to electrical signals which the transmitter
104
can then send. Device
100
also includes a receiver
112
connected to a speaker
114
. The transmitter
104
and the receiver
112
normally share an antenna
110
, although separate antennas may instead be provided.
The transmitter
104
includes, inter alia, a speech coder
120
for encoding the electrical voice signals and forwards them to a modulator
122
. Depending on the power mode and network used, the modulator
122
mixes the coded signals to the appropriate frequency band. For example, modulator
122
shifts the signal to approximately 800 MHz in the case of CDMA or 1900 MHz in the case of Wideband CDMA (WCDMA). Power amplifier/load switch
124
amplifies and impedance matches the signal. The load switch portion of the power amplifier/load switch
124
matches the outgoing signal to the required impedance and may also filter out various signal harmonics. Matching impedances helps an amplifier maximize power efficiency and filtering harmonics reduces interference. An isolator
106
and a receive/transmit duplexer
108
connect the power amplifier/load switch circuit
124
and antenna
110
. Using this series of components the handset
100
may transmit RF signals using the antenna
110
.
The receiver
112
obtains a received RF signal from the antenna
110
via the duplexer
108
. An RF receiver
130
prepares the received RF signal for demodulation. A demodulator
132
demodulates the received RF signal to output a demodulated signal, and a speech decoder
134
decodes the demodulated signal to form an audio signal for reproduction on speaker
114
.
Considerable power in a wireless communication device is dissipated in the power amplifier (PA) (e.g., power amplifier/load switch
124
) and the efficiency of a power amplifier is predominately determined by its output load design. There are two main factors affecting the output load design: 1. class of operation (e.g., class -A, -A/B, -B, -C, -E, etc.); and 2. load impedance at the fundamental and harmonic frequencies. In a typical PA design, the load is designed to achieve the best efficiency performance at its highest output power. For those power amplifiers that need to have low signal distortion (such as CDMA PA), there are the additional linearity requirements that need to be satisfied.
Wireless communication devices typically transmit RF signals at a plurality of power levels. However, the efficiency of the PA significantly varies over the output power range. Because current drain efficiency of the PA is most affected at a higher output power, the PA is designed to maximize efficiency at higher output power levels. One technique to improve power efficiency requires switching the quiescent current of the PA in response to a PA output high power (HP)/low power (LP) mode control change. At the HP mode, the PA is biased with high quiescent current in order to maximize its output current swing; at the LP mode, the PA is biased with low quiescent current in order to reduce current consumption. Another circuit technique that could be considered to improve the efficiency for varied output power system is by load switching—i.e., the output load is adjusted in accordance to the output power requirements.
Operational efficiency of a power amplifier is dependent on load impedance. A PA is generally designed for maximum output power operation. This usually means the output device “sees” a low impedance load. This is necessary to maximize the device's current swing. However, this low impedance unavoidably leads to a degraded efficiency when the output power level is lowered. In order to achieve improved efficiency performance at lower output power, the output device needs to “see” a high impedance load. A switched load circuit is a circuit implementation which provides a two-state (or multi-state) load design—i.e., a low impedance state for high power operation and a high impedance state for low power operation. Hence, the load is adjusted via a “switching” operation.
The trend of cellular wireless communication is moving toward a multi-mode handset. To simplify the implementation of a multi-mode handset, it is desirable to have components that can operate in multiple frequency bands. This is usually not too difficult a task for many RF components; however, a multi-mode PA is hard to realize because of the narrow band nature of the PA and to its low output load impedance. One method to overcome this problem is to use a switched load technique that can switch the load to the designated impedance in accordance with the selected frequency band.
U.S. Pat. No. 5,774,017 (issued to Adar) (henceforth referred to as the '017 patent), teaches a multiple-band amplifier. More particularly, it discloses a GaAs MMIC dual-band amplifier for wireless communications for operation at either the 80
Anadigics Inc.
Morgan & Lewis & Bockius, LLP
Nguyen Long
LandOfFree
Power amplifier with load switching circuit 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 with load switching circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power amplifier with load switching circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3276313