|
Mobile Phone Patent Abstract
An amplifier for use in a mobile phone for supplying a signal (I.sub.o)
to a load (Z.sub.L) comprises a first transistor (T.sub.1) having
a first main terminal coupled to a reference terminal (GND), a control
terminal, and a second main terminal for supplying the signal (I.sub.o)
to the load (Z.sub.L), and sensing means for determining the value
of the signal (I.sub.0). The sensing means comprises a second transistor
(T.sub.2) having a first main terminal coupled to the first main
terminal of the first transistor (T.sub.1), a control terminal coupled
to the control terminal of the first transistor (T.sub.1), and a
second main terminal for supplying a further signal (I.sub.F) which
is a representation of the signal (I.sub.o). The amplifier comprises
detection means (DMNS) for supplying a DC-component (I.sub.DC2)
of the further signal (I.sub.F). The detection means (DMNS) comprises
a resistor (R) coupled between a power supply terminal (V.sub.DD)
and the second main terminal of the second transistor (T.sub.2),
and a capacitor (C) coupled between the second main terminal of
the second transistor (T.sub.2) and the reference terminal (GND)
or the power supply terminal (V.sub.DD). The DC-component of the
signal (I.sub.0) is proportional to the signal (I.sub.0) and is
thus also proportional to the power supplied to the load (Z.sub.L).
Since the further signal (I.sub.F) is a representation of the signal
(I.sub.0) supplied to the load (Z.sub.L), the DC-component (I.sub.DC2)
of the further signal (I.sub.F) is a measure for the power supplied
to the load (Z.sub.L).This measure can be used to monitor the amount
of power supplied to the load (Z.sub.L) and possibly to regulate
the power to a desired level.
Mobile Phone Patent Claims
What is claimed is:
1. An amplifier for supplying a signal (I.sub.0) to a load (Z.sub.L),
comprising a first transistor (T.sub.1) having a first main terminal
connected to a reference terminal (GND), a control terminal, and
a second main terminal for supplying the signal (I.sub.0) to the
load (Z.sub.L), and sensing means for determining the value of the
signal (I.sub.0), characterized in that the sensing means comprises
a second transistor (T.sub.2) having a first main terminal connected
to the first main terminal of the first transistor (T.sub.1), a
control terminal connected to the control terminal of the first
transistor (T.sub.1), and a second main terminal for supplying a
further signal (I.sub.F) which is a representation of the signal
(I.sub.0), and in that the amplifier comprises detection means (DMNS)
having a control terminal (CNTRL) for measuring the further signal
(I.sub.F).
2. A mobile phone comprising a transmitter having an antenna for
transmitting a modulated high-frequency signal, comprising an amplifier
of the type as claimed in claim 1, wherein the load (Z.sub.L) is
formed by the antenna.
3. An amplifier as claimed in claim 1, characterized in that the
detection means (DMNS) comprises a circuit having a resistor (R)
and a capacitor (C) for supplying a DC-component of the further
signal (I.sub.F).
4. An amplifier as claimed in claim 3, characterized in that the
control terminal (CNTRL) is coupled to measure said DC-component.
5. An amplifier as claimed in claim 4, characterized in that the
DC-component is an DC voltage across the resistor (R).
6. An amplifier as claimed in claim 3, characterized in that the
resistor (R) is connected between a power supply terminal (V.sub.DD)
and the second main terminal of the second transistor (T.sub.2),
and the capacitor (C) is connected between the second main terminal
of the second transistor (T.sub.2) and the reference terminal (V.sub.DD).
7. An amplifier as claimed in claim 3, characterized in that the
resistor (R) is connected between a power supply terminal (V.sub.DD)
and the second main terminal of the second transistor (T.sub.2),
and the capacitor (C) is connected between the second main terminal
of the second transistor (T.sub.2) and the power supply terminal
(V.sub.DD).
8. An amplifier as claimed in claim 1, characterized in that the
main terminals of both the first and second transistors (T.sub.1,
T.sub.2) are directly connected to the reference terminal (GRD).
9. An amplifier as claimed in claim 6, characterized in that the
resister (R) is directly connected to the power supply terminal
(V.sub.DD).
10. An amplifier as claimed in claim 7, characterized in that the
resistor (R) is directly connected to the power supply terminal
(V.sub.DD).
Mobile Phone Patent Description
BACKGROUND OF THE INVENTION
The invention relates to an amplifier for supplying a signal to
a load, comprising a first transistor having a first main terminal
coupled to a reference terminal, a control terminal, and a second
main terminal for supplying the signal to the load, and sensing
means for determining the value of the signal.
Such an amplifier is known from the U.S. Pat. No. 5,285,143.
In the known amplifier, a sense current is generated from a load
current which is scaled down such that the sense current is an accurate
representation of the load current but has a substantially smaller
magnitude. The scaled down sense current is generated by coupling
a power sense resistor in series with the load current and develops
a load voltage across this resistor. A sense voltage, being substantially
equal to the load voltage, is applied to a pilot sense resistor
by a voltage follower. The pilot sense resistor is some predetermined
ratio of the power sense resistor. The sense current flowing through
the pilot sense resistor is scaled down in accordance with the ratio
of the power resistor to the pilot sense resistor. A current mirror
supplies current to the voltage follower.
A problem of the known amplifier is that a sensing element, for
example formed by a resistor, is coupled in series with the first
transistor. Though a high accuracy of the sense signal (current)
can be accomplished in this manner in principle, the circuitry needed
in order to reach this accuracy is quite complicated.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an amplifier which
eliminates the above-mentioned problem.
To this end, according to the invention, the amplifier of the type
defined in the opening paragraph is characterized in that the sensing
means comprises a second transistor having a first main terminal
coupled to the first main terminal of the first transistor, a control
terminal coupled to the control terminal of the first transistor,
and a second main terminal for supplying a further signal which
is a representation of the signal, and in that the amplifier comprises
detection means for supplying a DC-component of the further signal.
The invention is based on the insight that for many applications,
and especially for mobile phones, amplifiers do not operate in the
so called class A mode in which the power consumption is relatively
high, but operate in a lower-energy mode, for example in the so
called class B or class C mode. In these modes the signal comprises
a DC component which is proportional to the signal and is thus also
proportional to the power supplied to the load. Since the further
signal is a representation of the signal supplied to the load, the
further signal also comprises a DC-component which is a measure
for the power supplied to the load. This measure can be used to
monitor the amount of power supplied to the load and possibly to
regulate the power to a desired level.
An embodiment of the invention may be characterized in that the
detection means comprises a resistor coupled between a power supply
terminal and the second main terminal of the second transistor,
and a capacitor coupled between the second main terminal of the
second transistor and the reference terminal. By so doing, a simple
implementation of the detection means is accomplished. As an alternative
solution the capacitor may also be connected between the second
main terminal of the second transistor and the power supply terminal.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described in more detail with reference to
the accompanying drawing, in which:
the sole FIGURE is a circuit diagram of an embodiment of an amplifier
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The FIGURE shows a circuit diagram of part of the amplifier which
comprises a first bipolar transistor T.sub.1, a second bipolar transistor
T.sub.2, and detection means DMNS formed by a resistor R and a capacitor
C. A load Z.sub.L is connected between the collector of the first
bipolar transistor T.sub.1 and a reference terminal GND. The emitters
of the first and the second bipolar transistors T.sub.1 -T.sub.2
are connected to the reference terminal GND. The collector of the
second bipolar transistor T.sub.2 is connected to a control terminal
CNTRL. The resistor R is connected between a power supply terminal
V.sub.DD and the control terminal CNTRL. The capacitor C is connected
between the control terminal CNTRL and the reference terminal GND
or, alternatively, between the control terminal CNTRL and the power
supply terminal (V.sub.DD) as shown by the dashed lines in the FIGURE.
The principle of operation of the circuit is as follows. The first
and second bipolar transistors T.sub.1 and T.sub.2 are dimensioned
such that the further signal current I.sub.F, which flows through
the first bipolar transistor T.sub.1, is a fraction of the signal
current I.sub.o, which signal current I.sub.o flows through the
first bipolar transistor T.sub.1 and through the load Z.sub.L. If
the first and second bipolar transistors T.sub.1 and T.sub.2 are
matched in a proper way, for instance by integrating both the first
and the second bipolar transistors T.sub.1 -T.sub.2 in the same
integrated circuit, the further signal current I.sub.F is an accurate,
but much smaller, copy of the signal current I.sub.o. Under the
assumption that the amplifier is, for example, operating in the
so-called class C mode, the signal I.sub.o comprises a DC-component
which is a measure for the signal I.sub.o and as a consequence it
is also a measure for the amount of power supplied to the load Z.sub.L.
Since the further signal I.sub.F accurately matches the signal I.sub.o,
the further signal I.sub.F also comprises a DC-component I.sub.DC2
which accurately matches the DC-component of the signal I.sub.o.
Thus the DC-component I.sub.DC2 is an accurate representation of
the amount of power supplied to the load Z.sub.L. The capacitor
C forms a short-circuit for AC-currents. For this reason only the
DC-component I.sub.DC2 flows through the resistor R, causing a DC-voltage
across the resistor R. This DC-voltage is made available via a control
terminal CNTRL. Since this DC-voltage is an accurate measure for
the power supplied to the load Z.sub.L, this DC-voltage can be used
to monitor the amount of power supplied to the load Z.sub.L and
possibly to regulate the power to a desired level.
Instead of bipolar transistors, other active amplifier elements,
such as field effect transistors, may alternatively be used.
The FIGURE also shows, in simplified form, a mobile phone, represented
by the dashed line box enclosing the circuitry, including an antenna
represented by load Z.sub.L and a transmitter including transistor
T.sub.1 connected to the load. |