U.S. patent application number 09/361865 was filed with the patent office on 2002-01-24 for method and system for efficiently transmitting energy from an rf device.
Invention is credited to AGAHI-KESHEH, DARIOUSH, OSKOWSKY, MARK.
Application Number | 20020008575 09/361865 |
Document ID | / |
Family ID | 23423737 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020008575 |
Kind Code |
A1 |
OSKOWSKY, MARK ; et
al. |
January 24, 2002 |
METHOD AND SYSTEM FOR EFFICIENTLY TRANSMITTING ENERGY FROM AN RF
DEVICE
Abstract
A method and system for efficiently transmitting RF energy from
a RF device is disclosed. The method and system comprises a
multi-stage power amplifier having a plurality of power amplifier
stages arranged in parallel with associated switches for
selectively switching on or off the plurality of power amplifier
stages to produce a desired power level. By selectively switching
on or off each individual power amplifier's associated switches at
predetermined operating point's produces the desired power level
for maximum efficiency. Additionally, more than one connected
multi-stage power amplifiers each having a plurality of power
amplifier stages arranged in parallel with associated switches for
selectively switching on or off the plurality of power amplifier
stages may be used to produce a desired power level.
Inventors: |
OSKOWSKY, MARK; (SAN JOSE,
CA) ; AGAHI-KESHEH, DARIOUSH; (IRVINE, CA) |
Correspondence
Address: |
SCOTT A. HORSTEMEYER
THOMAS, KAYDEN, HORSTEMEYER & RISLEY, L.L.P.
100 GALLERIA PARKWAY
SUITE 1750
ATLANTA
GA
30339
US
|
Family ID: |
23423737 |
Appl. No.: |
09/361865 |
Filed: |
July 27, 1999 |
Current U.S.
Class: |
330/51 ;
330/124R |
Current CPC
Class: |
H03F 1/0277
20130101 |
Class at
Publication: |
330/51 ;
330/124.00R |
International
Class: |
H03F 001/14; H03F
003/68 |
Claims
What is claimed is:
1. A method for efficiently transmitting RF energy from an RF
device comprising the steps of: determining a desired power level
from a plurality of pre-set power levels for transmitting RF energy
from an RF device; and selectively switching on or off one or more
power amplifier stages arranged in parallel to produce the desired
power level.
2. The method for efficiently transmitting RF energy according to
claim 1, wherein each one of the power amplifier stages: operate at
a predetermined operating point for maximum efficiency.
3. The method for efficiently transmitting RF energy according to
claim 1, wherein the power amplifier stages are arranged in
parallel to form a multi-stage power amplifier, whereby selectively
switching on or off one or more of power amplifier stages produces
the desired power level.
4. The method for efficiently transmitting RF energy according to
claim 1, wherein the power amplifier stages utilizing three power
amplifier stages arranged in parallel to form a multi-stage power
amplifier, whereby selectively switching on or off individual power
amplifier stages at predetermined operating points produces the
desired power level at maximum efficiency.
5. The method for efficiently transmitting RF energy according to
claim 1, wherein one or more connected multi-stage power amplifiers
are utilized, each multi-stage power amplifier having more than one
power amplifier stage arranged in parallel; whereby selectively
switching on or off one or more of the power amplifier stages in
the multi-stage power amplifiers produces the desired power
level.
6. The method for efficiently transmitting RF energy according to
claim 1, wherein producing the desired power level, further
comprises the step of: storing the plurality of power levels and
associated combinations for independently switching on or off the
one or more power amplifier stages for use in selectively utilizing
one or more power amplifier stages for producing a desired power
level from the stored plurality of power levels.
7. A system for efficiently transmitting RF energy from an RF
device comprising the steps of: A plurality of power amplifier
stages arranged in parallel; a controller for determining a desired
power level from a plurality of power levels for transmitting RF
energy from an RF device; and a plurality of switches for
selectively switching one or more power amplifier stages arranged
in parallel on or off to produce the desired power level.
8. The system according to claim 7, wherein each one of the power
amplifier stages are operated at a predetermined operating point
for maximum efficiency.
9. The system according to claim 7, further comprising: switches
for selectively switching one or more of three power amplifier
stages arranged in parallel to form a multi-stage power amplifier
on or off to produce the desired power level.
10. The system according to claim 7, further comprising: switches
for selectively switching one or more power amplifier stages
arranged in parallel in one or more connected multi-stage power
amplifiers on or off to produce the desired power level.
11. The system according to claim 7, further comprising: memory for
storing the plurality of power levels and associated combinations
for independently switching the one or more power amplifier stages
on or off.
12. A multi-stage power amplifier comprising: a plurality of power
amplifier stages arranged in parallel; and switches associated with
the plurality of power amplifier stages for selectively switching
the plurality of power amplifier stages on or off to produce a
desired power level.
13. The multi-stage power amplifier according to claim 12, wherein
each power amplifier stage has predetermined operating points.
14. The multi-stage power amplifier according to claim 12, further
comprising: three power amplifier stages arranged in parallel to
form a multi-stage power amplifier wherein selectively switching
one or more of the three power amplifier stages on or off produces
a desired power level.
15. The multi-stage power amplifier according to claim 12, further
comprising: three power amplifier stages arranged in parallel to
form a multi-stage power amplifier wherein selectively switching
individual power amplifier stages at predetermined operating points
on or off produces a desired power level at maximum efficiency.
16. The multi-stage power amplifier according to claim 12, further
comprising: one or more connected multi-stage power amplifiers,
each said multistage power amplifier having more than one power
amplifier stage arranged in parallel wherein selectively switching
one or more of said power amplifier stages in the one or more
multi-stage power amplifiers produces a desired power level.
17. The multi-stage power amplifier according to claim 12, further
comprising: a ROM for storing a plurality of power levels and
associated combinations for independently switching the plurality
of power amplifier stages on or off for selectively utilizing the
plurality of power amplifier stages to produce a desired power
level from the stored plurality of power levels.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to power amplifiers
used for transmitting RF energy and, in particular, to a
multi-stage amplifier wherein the stages are arranged in parallel
and switchably turned on or off to provide a desired plurality of
power levels with each stage operating at a predetermined operating
point.
[0003] 2. Description of Related Art
[0004] A power amplifier of one type or another is used as the
final stage in any RF transmission device. In a cellular telephone,
for example, the power amplifier receives a signal as an input and
then amplifies that signal to a power level that may be effectively
coupled to an antenna and transmitted as RF radiation. Currently,
most power amplifiers utilize multiple amplifier stages connected
in series to form a multistage power amplifier. In the modern
transceiver the transmitted power is adjusted by varying the series
connected power amplifier's bias voltage or current.
[0005] However, by adjusting the bias voltage or current in a
series connected multistage amplifier for a plurality of power
levels, the efficiency is known to be 60% or less resulting in
wasted power to heat. Therefore, there is a need for a multi-stage
power amplifier that is capable of operating at a plurality of
power levels at a higher overall average efficiency. The subject
invention solves this problem in a new and unique manner not
previously known in the arts.
SUMMARY OF THE INVENTION
[0006] The method and system comprises a multi-stage power
amplifier having a plurality of power amplifier stages arranged in
parallel with associated switches for selectively switching the
plurality of power amplifier stages on or off to produce a desired
power level.
[0007] Selectively switching on or off each individual power
amplifier's associated switches at predetermined operating point's
produces the desired power level for maximum efficiency.
Additionally, more than one connected multi-stage power amplifier,
each having a plurality of power amplifier stages, arranged in
parallel with associated switches for selectively switching on or
off the plurality of power amplifier stages may be used to produce
a desired power level.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The exact nature of the invention, as well as the preferred
mode of use, and its objects and advantages will be readily
understood by reference to the following detailed description of an
illustrative embodiment when read in conjunction with the
accompanying drawings in which like reference numerals designate
like parts throughout the figures thereof, and wherein:
[0009] FIG. 1 is a block diagram of a prior art power amplifier
system comprising a series configured arrangement of stages;
[0010] FIG. 2 is a graph showing the non-linear relationship
between PWR OUT and the common control signal V.sub.control
provided to the stages of the power amplifier in FIG. 1;
[0011] FIG. 3 is an efficiency curve showing the overall
transmission efficiency as a function of the control signal;
and
[0012] FIG. 4 is a block diagram of a multi-stage power amplifier
according to the present invention having a plurality of
parallel-arranged stages that are independently controlled between
an OFF state and an ON state.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Referring now to the drawings, FIG. 1 shows a high-level
block diagram of a prior art power amplifier system 10 comprising a
series configured arrangement of power amplifier stages. The power
amplifier system 10 utilizes a conventional, multistage power
amplifier 12 wherein three separate power amplifier (PA) stages 14,
16 and 18, respectively, take a PWR IN 20 signal and through a
matching network 24 produce a PWR OUT signal 22. The multi-stage
amplifier of FIG. 1 uses several power amplifier stages rather than
merely one power amplifier stage such that the overall PA 12 may
achieve the desired amplification, approx., 20 dB gain, typically
required by a cellular telephone with higher fidelity and with less
probability of oscillation.
[0014] In many systems employing RF transmission, it is becoming
more and more commonplace to require a plurality of power levels in
a cellular telephone based on today's telecommunication standards.
By way of example, but not of limitation, current mobile transmit
stations (MTS) are required to transmit at 15 different power
levels that are designated as PWR LVL 5 to PWR LVL 19 which vary in
2 dBm steps from 5 dBm to 33 dBm. The different power levels are
determined by the cellular telephone's proximity to the MTS for
maintaining an RF link. The multi-stage PA 12 of FIG. 1 implements
the required power level by suitably controlling the voltage on a
V.sub.CONTROL 26 line that is provided to each of the PA stages and
may be suitably varied between two known values that are set in the
factory during the calibration process. In an RF device (not shown)
such as a cellular phone, the transceiver portion adjusts the
transmitted power by varying the PA's 12 bias voltage or current
through the V.sub.CONTROL 26 line by a PA controller 28 in response
to the cellular phones digital signal processor (DSP) 30 which
determines its location and associated power level with respect to
its location to its MTS. The PA controller 28 further monitors the
PWR OUT 22 by a coupler 32 to further tune and adjust the
multi-stage PA 12, as shown in FIG. 1.
[0015] Referring now to FIG. 2, there is shown a graph 34 depicting
the non-linear relationship 36 between PWR OUT 22 and the common
control signal V.sub.CONTROL 26 provided to the stages of the power
amplifier 12 in FIG. 1. As shown by FIG. 2, the relationship 36
between PWR OUT 22 and V.sub.CONTROL 26 is not linear, as
V.sub.CONTROL ranges from 0 to 3 volts. In addition, turning to
FIG. 3, there is depicted an efficiency curve 40 showing the
overall transmission efficiency 38 as a function of the control
signal 26. As shown by FIG. 3, the power amplifier has a maximum
efficiency at a particular operating point 42 (e.g. 60% at 2
volts). Consequently, as the power amplifier 12 is variably set to
different power levels, the overall efficiency of the power
amplifier 12 is generally less than the maximum efficiency of 60%.
If the transmitter's power amplifier always operates in the range
identified as 5 dBm 33 dBm, then the power amplifier 12 has an
overall average efficiency that is even less than 60% (e.g. 52%).
As a result, approximately only one half of the power being
inserted in the device is actually being transmitted as useful RF
power, whereas the rest of the power is merely being dissipated as
heat.
[0016] Operating as efficiently as possible is critical when it
comes to a portable device. A 3-volt device that transmits at 2
watts of power at 100% efficiency, for example, draws two-thirds of
an ampere. If that same device were to operate at 60% efficiency,
its current draw when transmitting at 2 watts of power would
increase to approximately 1.1 amperes. Given a typical battery
capacity of only 1 ampere-hour, this 60% efficiency device would
have a total transmit time or "talk time" of less than 1 hour.
[0017] Referring now to FIG. 4, there is shown a block diagram 60
of the multistage power amplifier according to the present
invention having a plurality of parallel-arranged power amplifier
stages that are independently controlled between an OFF state and
an ON state for maximizing the power in 20 to power out 22
efficiency to solve the above-described drawbacks. In accordance
with the present invention, the method for efficiently transmitting
RF energy from an RF device such as a cellular phone comprises the
step of determining a desired power level for the power out 22 from
a plurality of power levels for transmitting RF energy from an RF
device based on its geographical location to a mobile transmit
station. This information is processed within the digital signal
processor (DSP) 30 and delivered to the power amplifier controller
56, as shown in FIG. 4. Within the power amplifier controller 56 is
a random access memory (RAM) which stores a predetermined plurality
of power levels and associated combinations for independently
switching on or off one or more of the power amplifier stages. It
should be understood that although a ROM is shown in FIG. 4, any
memory device may be used.
[0018] From the desired power level delivered by the DSP 30, the PA
controller 62 utilizing the stored information in the ROM 62 to
selectively power or switch on or off the combination of power
amplifier stages arranged in parallel for producing the desired
power level. In one preferred embodiment, three power amplifier
stages 44, 46 and 48 are arranged and connected in parallel to form
a multi-stage power amplifier. By selectively switching on or off
each individual power amplifier's associated switches 50, 52 and 54
at predetermined operating point's produces the desired power level
(PWR OUT) 22 through summer 64 for maximum efficiency.
[0019] Although not shown, in another preferred embodiment, a
plurality of multistage power amplifiers may be connected together
wherein each multi-stage power amplifier has more than one power
amplifier stage arranged in parallel for also selectively switching
on or off one or more of the power amplifier stages in one or more
multi-stage power amplifiers to produce the desired power
level.
[0020] While the invention has been particularly shown and
described with reference to a preferred embodiment, it will be
understood by those skilled in the art that various changes in form
and detail may be made therein without departing from the spirit
and scope of the invention.
[0021] Those skilled in the art will appreciate that various
adaptations and modifications of the just-described preferred
embodiments can be configured without departing from the scope and
spirit of the invention. Therefore, it is to be understood that
within the scope of the appended claims, the invention may be
practiced other than as specifically described herein.
* * * * *