Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-03-16
2003-07-22
Kincaid, Lester G. (Department: 2681)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S127500, C455S115200, C455S120000, C330S130000
Reexamination Certificate
active
06597925
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic circuitry, and, in particular, to power amplifiers for telecommunication applications.
2. Description of the Related Art
Wireless telecommunication systems typically operate over specific ranges of signal frequencies. For example, according to the U.S. PCS (Personal Communication System) standard for CDMA (code-division, multiple-access) communications, forward-link transmissions from base stations to mobile units occur within the 60-MHZ frequency range from 1930 MHZ to 1990 MHZ. (Reverse-link transmissions from the mobile units back to the base stations occur within a different frequency range.) The 60-MHZ forward-link transmit frequency range is divided into six frequency blocks: three 15-MHZ frequency blocks, each with eleven 1.25-MHZ frequency channels, and three 5-MHZ frequency blocks, each with three 1.25-MHZ frequency channels, for a total of 42 frequency channels, where each frequency channel can support up to, for example, 64 different CDMA code channels.
When configured in the field, a particular base station is assigned to operate within a particular PCS frequency block. In order to avoid having to design, build, and inventory six different types of base station transmitters (one for each different PCS frequency block), a single generic base station transmitter design is typically used for all frequency blocks. In that case, it is important that the generic base station transmitter operate satisfactorily at all frequencies within the 60-MHZ forward-link transmit frequency range.
FIG. 1
shows a block diagram of a conventional base station transmitter circuit
100
used in the forward-link transmitters of PCS telecommunication systems. Base station transmitter circuit
100
has an oscillator
102
that generates an RF (radio frequency) signal
104
having a frequency between 869 MHZ and 894 MHZ, and a transmit up-converter
106
that converts RF signal
104
into a PCS block signal
108
having a frequency corresponding to one of the PCS frequency blocks within the 1930-1990 MHZ PCS range (e.g., the center frequency for a particular 5-MHZ or 15-MHZ PCS frequency block). The particular PCS frequency block is specified by a digital control signal
120
received from alarm control board (ACB)
118
.
PCS block signal
108
generated by up-converter
106
is then provided to high-power amplifier
110
, which further amplifies the PCS block signal to generate an amplified PCS block signal
112
for subsequent transmitter processing (e.g., tuning to a particular PCS frequency channel within the PCS frequency block, data and code modulation, and transmission) (not shown in FIG.
1
). In one implementation of base station transmitter circuit
100
, high-power amplifier
110
is a Model No. 34874/EB500600-3 amplifier from MPD Technologies, Inc., a subsidiary of Microwave Power Devices, Inc., of Hauppauge, N.Y.
In addition, as indicated in
FIG. 1
, an amplifier alarm signal
114
is fed back to transmit up-converter
106
from high-power amplifier
110
to indicate the presence of an alarm condition within high-power amplifier
110
. A transmit up-converter alarm signal
116
is also fed back to alarm control board
118
from transmit up-converter
106
to indicate the presence of an alarm condition within either transmit up-converter
106
or high-power amplifier
110
.
FIG. 2
shows a block diagram of a conventional transmit up-converter
106
for base station transmitter circuit
100
of FIG.
1
. As shown in
FIG. 2
, up-converter
106
receives RF signal
104
from oscillator
102
of
FIG. 1
at 1-dB pad
202
. Mixer
206
mixes the received RF signal with a mixing signal
224
from low-pass filter
222
to convert the received RF signal into a mixer output signal
204
having the desired PCS block frequency. Mixer output signal
204
is processed through potentiometer
208
, 5-dB amplifier
210
, 20-dB amplifier
212
, and band-pass filter
214
to generate PCS block signal
108
for transmission to high-power amplifier
110
of FIG.
1
.
Synthesizer
218
receives control signal
120
from ACB
118
and, in conjunction with 5-dB amplifier
220
and low-pass filter
222
, converts a 15-MHZ local clock signal
216
into mixing signal
224
having a frequency appropriate to cause mixer
206
to generate mixer output signal
204
having the desired PCS block frequency specified by control signal
120
. Synthesizer
218
, which may comprise a phase-locked loop circuit or other controllable signal generator, generates a lock detect signal
226
to indicate when the desired frequency for mixing signal
224
has been achieved.
Logic circuits
228
(1) receive lock detect signal
226
from synthesizer
218
and amplifier alarm signal
114
from high-power amplifier
110
and (2) generate control signals
230
for voltage regulators and switches
232
, which in turn generate signals to control the gains of amplifiers
210
,
212
, and
220
. In addition, transmit up-converter alarm signal
116
is fed back from logic circuits
228
to alarm control board
118
.
In telecommunication systems, it is important to limit intermodulation distortion (IMD) (also known as spectral regrowth (SR) in CDMA systems). Intermodulation distortion is a key performance-degrading effect in an amplifier, because it causes interference to adjacent channels that cannot be filtered out. IMD is a non-linear effect that is caused by the amplifier's input power-output power characteristics being non-linear rather than linear. The non-linear characteristic is due to the physical properties of the semiconductor material used to fabricate the power transistors used in the amplifier. To get a linear input-output characteristic, some form of linearization, such as feed-forward and/or predistortion, is typically used, but it still usually does not provide optimum performance over a wide frequency range.
Thus, although an amplifier can be sufficiently optimized over a specific narrow frequency range (e.g., up to about a 20-MHZ frequency range), it is difficult to optimize a single amplifier to provide low levels of IMD across the entire 60-MHZ frequency range that PCS base station forward-link transmitters need to be able to support. One option is to design amplifiers, such as high power amplifier
110
of
FIG. 1
, to be so-called smart amplifiers that have complicated circuitry (e.g., frequency detection circuitry) that measures the frequency of the received signal, such as PCS block signal
108
of
FIG. 1
, and then automatically optimizes the operations of the amplifier accordingly based on that measured frequency. Unfortunately, such an option is often cost prohibitive for implementation in the base stations of typical PCS telecommunication systems. As a result, typical base station amplifiers, such as base station transmitter circuit
100
of
FIG. 1
, are optimized during manufacturing as best as possible for the entire 60-MHZ PCS forward-link frequency range, and then no optimization is performed when the base station is subsequently configured in the field (when the particular PCS frequency block for the base station is first known).
SUMMARY OF THE INVENTION
The present invention is directed to a transmitter circuit with frequency self-optimization for use in base station forward-link transmitters of wireless telecommunication systems conforming, for example, to the U.S. PCS standard. The self-optimizing base station transmitter circuit of the present invention uses digital information, already available in conventional base station transmitter circuits after they are configured for operation in the field, that indicates the specific PCS frequency block assigned to the base station, to optimize amplifier operations based on the specified PCS frequency block. As a result, the self-optimizing base station transmitter circuit can provide better performance (e.g., lower intermodulation distortion) over the entire 60-MHZ PCS frequency range than that provided by conventional base station transmitter circui
Garcia Jose M.
Levitine Vladimir
Agere Systems Inc.
Kincaid Lester G.
Mendelsohn Steve
Ward Ronald J.
LandOfFree
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