Telecommunications – Transmitter – Measuring – testing – or monitoring of transmitter
Reexamination Certificate
1999-02-01
2002-01-15
Bost, Dwayne (Department: 2681)
Telecommunications
Transmitter
Measuring, testing, or monitoring of transmitter
C455S550100, C455S063300, C455S067150, C324S647000, C330S110000
Reexamination Certificate
active
06339702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an output power detection circuit of a transmitter and, more particularly, to an output power detection circuit having no temperature dependency.
2. Description of the Related Art
An output power detection circuit of a conventional transmitter will be described with reference to
FIG. 2. A
transmission signal is amplified by a driver amplifier
31
and is further amplified by a power amplifier
32
to a predetermined output power, and the resultant signal is supplied to an isolator
33
. The signal is transmitted from an antenna (not shown) via an antenna sharing device (not shown).
A part of the transmission signal from the power amplifier
32
is supplied to an output power detection circuit (hereinafter, called a detection circuit)
34
where a voltage (detection voltage) proportional to the output power is detected.
The detection voltage is amplified by a dc amplifier
35
and is converted into a digital signal by an A/D converter
36
. The digital signal is inputted to a not-illustrated control circuit, properlyprocessed, and outputted as a control signal. The control signal controls the amplification degree of the driver amplifier
31
to make the output power from the power amplifier
32
constant.
The detection circuit
34
has two detection diodes
42
and
43
to which a bias current in the forward direction is applied by a voltage from a power source terminal
41
. The cathode of the detection diode
42
and the anode of the other detection diode
43
are connected, so that the two detection diodes
42
and
43
are connected in series. The cathode of the detection diode
43
is connected to the ground via voltage dividing resistors
44
and
45
which are connected in series.
A part of the transmission signal from the power amplifier
32
is supplied to a connection point between the cathode of the detection diode
42
and the anode of the detection diode
43
via a coupling capacitor
46
and a series resistor
47
. The anode of the detection diode
42
is connected to the ground via a direct current blocking capacitor
48
and the cathode of the detection diode
43
is connected to the ground via a smoothing capacitor
49
.
In the above construction, when a part of the transmission signal from the power amplifier
32
is supplied to the detection circuit
34
, it is rectified by the two detection diodes
42
and
43
and a detection voltage proportional to the output power is obtained from the connection point between the voltage dividing resistors
44
and
45
.
In the above construction, since the static characteristics of the detection diodes
42
and
43
have temperature dependency, when the temperature around the detection diodes
42
and
43
changes, the detection voltage is changed accordingly. Consequently, there is a problem that an accurate output electric power cannot be detected.
That is, for instance, when the ambient temperature rises, the static characteristic of the detection diodes
42
and
43
changes in such a manner that the forward current increases, thereby increasing the bias current. As a result, the detection voltage appearing at the connection point of the voltage dividing resistors
44
and
45
also increases. The detection voltage increases by the increase in the bias current flowing in the detection diodes
42
and
43
, so it is not the output power which is accurately detected. For example, when the amplification degree of the driver amplifier
31
is controlled on the basis of the detection voltage, a predetermined output power cannot be therefore obtained.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an output power detection circuit of a transmitter, which can accurately detect an output power from a power amplifier without depending on a change in ambient temperature.
In order to realize the object, an output power detection circuit of a transmitter of the invention comprises: a first diode to which a first load resistor is connected in series and through which a first bias direct current flows; a second diode to which a second load resistor is connected in series and through which a second bias direct current flows; and a differential amplifier in which a first voltage generated in the first load resistor is applied to one of input terminals and a second voltage generated in the second load resistor is applied to the other input terminal. It is set so that the first voltage generated in the first load resistor by the first bias direct current and the second voltage generated in the second load resistor by the second bias direct current are made equal. By adding a part of a transmission signal outputted from the power amplifier to the first diode, a voltage according to the power of the transmission signal is detected from the differential amplifier.
According to an output power detection circuit of a transmitter of the invention, the first and second diodes have static characteristics which are the same, the first and second load resistors are set to have resistance values which are equal, and the first and second bias direct currents are applied from the same power source.
According to an output power detection circuit of a transmitter of the invention, at least one of the first and second load resistors is constructed by including a variable resistor.
According to an output power detection circuit of a transmitter of the invention, each of the first and second diodes has two diodes which are connected in series, a transmission signal from the power amplifier is inputted to the connection point of the two diodes which construct the first diode, and the transmission signal is rectified to a double voltage by the two diodes constructing the first diode.
REFERENCES:
patent: 3577139 (1971-05-01), Foerster
patent: 4637003 (1987-01-01), Yokogawa
patent: 4841177 (1989-06-01), Sugiyama et al.
patent: 5589682 (1996-12-01), Brown et al.
patent: 5659253 (1997-08-01), Busking
patent: 5742201 (1998-04-01), Eisenberg et al.
patent: 5801552 (1998-09-01), Moore
patent: 5898337 (1999-04-01), Inahasi
patent: Hei 8-148952 (1996-06-01), None
patent: Hei 9-55668 (1997-02-01), None
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