Telecommunications – Transmitter – With feedback of modulated output signal
Reexamination Certificate
1999-09-10
2003-10-14
Trost, William (Department: 2683)
Telecommunications
Transmitter
With feedback of modulated output signal
C455S127500, C455S069000, C455S115200, C455S343200
Reexamination Certificate
active
06633750
ABSTRACT:
FIELD OF THE INVENTION
The present inventions are directed to methods and apparatus for operating a mobile unit more efficiently and linearly over a range of given RF signal output power levels.
In accordance with an aspect of the present inventions, the DC power consumed by a wireless communications mobile handset is regulated by transmitting an RF power output designating signal from a base station, wherein the RF power output designating signal indicates a desired power level of an RF signal output from the mobile handset. The RF power output designating signal is then received by the mobile handset, where it is used to set the level of the DC power provided to the mobile handset. Preferably, the level of the DC power is set to the minimum value necessary to maintain linear operation of an RF amplifier circuit contained within the mobile handset. The level of the DC power can be set by generating a control signal within the mobile handset. The level of the control signal is selected based on the RF power output designating signal. By way of non-limiting example, the control signal level can be selected from a plurality of control signal levels, wherein the control signals correspond to a respective plurality of RF power output levels. Thus, the control signal level corresponding to the RF power output level designated by the RF power output designating signal will be selected.
In accordance with a further aspect of the present invention, the DC power level is varied from the set DC power level in proportion to an envelope of the RF output signal. This can be accomplished by sensing the envelope of the RF output signal to produce a sampled envelope signal, which can then be added to the control signal.
In accordance with still a further aspect of the present inventions, a feedback loop, in conjunction with the control signal, can be used to set the level of the DC power. By way of non-limiting example, a supply current tracking signal, which indicates the present level of current supplied to an RF amplifier circuit contained in the mobile handset, is generated. The difference between the control signal and the supply current tracking signal is determined to obtain a biasing signal. The supply current, and thus the DC power supplied to the RF amplifier circuit, is then varied in proportion to the biasing signal. Alternatively, a supply voltage tracking signal, which indicates the present level of voltage supplied to the RF amplifier circuit, is generated. The difference between the control signal and the supply voltage tracking signal is determined to obtain the biasing signal. The supply voltage, and thus the DC power supplied to the RF amplifier circuit, is then varied in proportion to the biasing signal.
In accordance with still a further aspect of the present inventions, the RF power output designating signal indicates the existence of either a high RF output power condition or a low RF output power condition. The RF input signal is amplified through a driver. During a high RF output power condition, the DC power is provided to the RF amplifier circuit, and the RF signal is further amplified through the RF amplifier circuit. During a low RF output power condition, the flow of DC power to the RF amplifier circuit is impeded, and further amplification of the RF input signal is bypassed.
To further enhance the linearity and efficiency of the RF amplifier circuit, various features of the above-mentioned embodiments can be combined.
The present invention pertains to power amplifiers, including more specifically, a power amplifier circuit for wireless communication systems.
BACKGROUND OF THE INVENTION
In wireless communication systems, mobile handsets communicate with other mobile handsets through base stations connected to the PSTN (public switched telephone network). Typically, in FDMA systems the base stations determine the frequencies at which the handsets are to communicate and send signals to the handsets to adjust the transmission power of the handsets.
The signals that are transmitted by the handsets are typically amplified prior to transmission to the base station. The amplification of the signal within the handset is generally performed by a radio frequency (RF) power amplifier
10
, a representative embodiment of which is depicted in
FIG. 1
(PRIOR ART). The RF power amplifier
10
includes a DC power terminal
12
and ground terminal
14
. A DC power source
16
is typically connected between the power terminal
12
and the ground terminal
14
, producing a supply voltage, V
S
, at the power terminal
12
and a supply current, I
S
, into the power terminal
12
. Thus, the RF power amplifier is supplied with a DC power, P
DC
, equal to V
S
*I
S
. An RF input signal, RF
in
, generated by the transmitting handset, is fed into the RF power amplifier
10
via an RF input terminal
18
. The RF power amplifier
10
amplifies the RF input signal, RF
in
, to produce an RF output signal, RF
out
, at an RF output terminal
20
. The RF output signal, RF
out
, after passing through signal processing circuits, is typically sent to the antenna for transmission. An RF input signal, RF
in
, has an average input signal power, P
in
, and an RF output signal, RF
out
, has an average output signal power, P
out
.
When transmitting a signal with a non-constant envelope from a handset it is desirable to operate the power amplifier
10
in a linear mode to minimize signal distortion and bandwidth required to transmit the signal. The linearity of the power amplifier, which is measured by the uniformity of the transfer characteristic (P
out
/P
in
), varies with I
S
, V
S
, and RF
out
. Referring to
FIG. 2
(PRIOR ART), the curves C
1
, C
2
, and C
3
represent compression characteristics of an RF power amplifier
10
of
FIG. 1
, given three exemplary amplifier DC power, P
DC
, levels. The line L represents linear operation of the amplifier
10
. As curves C
1
, C
2
, and C
3
illustrate, the linearity of the power amplifier depends on P
DC
. That is, as P
DC
, increases, the range of P
in
values for which the amplifier remains linear increases. In general, the output power, P
out
, for which a power amplifier compresses increases with the DC power supplied to the power amplifier.
Although supplying a relatively high DC power to the RF power amplifier
10
will generally maintain linear operation of the RF power amplifier
10
, such an arrangement becomes less advantageous in a system with varying transmission power requirements. A wireless communications system restricts the transmission power of the handset to minimize the signal from propagating to an excessively far point, so that the same frequency may be used at a far point, i.e., in other cells in order to permit servicing of as many subscribers as possible within the finite frequency resources allocated to the system. At the same time, the transmission power must be high enough to maintain the integrity of the transmitted signal over the distance that it travels to a base station. The magnitude of the handset transmission power required to maintain proper communication with a base station is dictated in part by the distance and the electrical communication environment between the handset and the base station. That is, if the handset is located far from a base station, the level of the RF output signal power, P
out
, will be relatively high. If the handset is located close to the base station, the level of the RF output signal power, P
out
, will be relatively low.
In a situation requiring a relatively low handset transmission power, an RF power amplifier that is supplied with a high DC power is inefficient. Referring to
FIG. 1
, the power the power amplifier
10
dissipates as heat is equal to the difference between the power supplied to the RF amplifier
10
, P
DC
and P
in
, and the RF output signal power, P
out
, as characterized by the equation, P
HEAT
=P
DC
+P
in
−P
out
. Thus, given a constant DC supply power, P
DC
, the lower the RF output signal power, P
out
, is, the more power the amplifier wastes as h
Dacus Farron L.
Morris Russell A.
Cool Kenneth J.
Ferguson Keith
Intel Corporation
Trost William
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