Amplifiers – With semiconductor amplifying device – Including particular biasing arrangement
Reexamination Certificate
2001-05-29
2003-04-08
Tokar, Michael (Department: 2819)
Amplifiers
With semiconductor amplifying device
Including particular biasing arrangement
C330S290000, C330S298000
Reexamination Certificate
active
06545541
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to power amplifiers and, in particular, to the detection of a bias level in power amplifiers.
In conventional wireless devices, power amplifiers in a given frequency band for a given communication standard are typically optimized to meet specifications for output power, gain, linearity, and attain a maximum efficiency given the previous constraints. The control of direct current (DC) quiescent current levels in power amplifiers for wireless devices may effect the control of gain, linearity, and low power efficiency in handset application. In addition, in Global Standard for Mobile Communications (GSM) applications, under radio frequency (RF) drive conditions the linear relationship between DC collector current and output RF voltage amplitude in saturated bipolar power amplifiers has been exploited by current sensing the collector current dynamically. Extensions of the use of saturated bipolar-based power amplifiers in architectures that enable linear amplification also may utilize current sensing of the DC current.
As seen in
FIG. 1
, conventionally, a series resistor
26
between the power supply and the power amplifier (PA)
20
detects the DC current levels. As is seen in
FIG. 1
, the DC voltage across the sense resistor
26
may be measured by operational amplifier
22
and fed back to a DC adjust circuit
24
which controls the DC bias of the PA
20
. Inductor
28
may filter any alternating current (AC) component from the voltage and inductor
30
may be provided for matching purposes.
When a series sense resistor
26
is utilized to measure DC current levels, the sense resistor
26
may lead to dissipated power depending on the resistor value. Furthermore, the sense resistor
26
typically is a high accuracy low value resistor to preserve efficiency which may be expensive. For small resistor values, the degradation in efficiency may be small and can be quantified according to:
&eegr;
w/Res
/&eegr;
w/oRes
=1−I
DC
R
SENSE
/V
DD
where is the total I
DC
current, R
SENSE
is the value of the sense resistor between the PA
20
and the power supply (typically a battery in a wireless device), and V
DD
is the power supply voltage. For a typical application of a 1 Watt RF output and 50% efficiency, with R
SENSE
=0.1 Ohm, and V
DD
=3.4 V the degradation in efficiency will be 2%. For a larger, 1 Ohm, resistor, the efficiency degradation is closer to 18%.
In addition to the incremental loss in peak efficiency, the accuracy of the current sensing system may be sensitive to the exact value of the very small resistance. Such high accuracy, extremely small resistance values may be costly and/or difficult to manufacture.
It is the inventor's belief that previously a single transistor from a multi-transistor power amplifier was used to measure DC current for the amplifier by providing a separate power feed to the single transistor.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide methods and systems for current sensing for an amplifier using an embedded cell. The embedded cell is a transistor cell from a plurality of transistor cells which is coupled to the other transistor cells so as to block DC current flow between the embedded cell and the other cells and allow AC current to flow between the embedded cell and the other cells. Power may be supplied to the embedded cell through a current sensing circuit, such as a resistor, which senses the DC current drawn by the embedded cell which reflects to the total DC current drawn by the by amplifier.
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Pehlke David R.
Whartenby James
Ericsson Inc.
Myers Bigel Sibley & Sajovec P.A.
Nguyen Khai
Tokar Michael
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