Amplifiers – With semiconductor amplifying device – Including protection means
Reexamination Certificate
2001-01-18
2001-12-11
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including protection means
C330S20700P, C455S115200
Reexamination Certificate
active
06329880
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to a transmitting circuit for a mobile communication equipment having an automatic output power control circuit (APC), and particularly relates to a transmitting circuit having a directional coupler capable of detecting power outputted from a final stage amplifier and a reflected wave generated by the mismatching between the output impedance of the final stage amplifier and a load impedance connected to the output side of the final stage amplifier, and allowing the gate voltage of the final stage amplifier to be switched depending on the amplitude of this reflected wave.
2. Description of the Prior Art
As a radio frequency power amplifier used in the transmitting circuit of a conventional transmitter, Japanese Patent Application Laid-Open No. 57-118412, for example, discloses a radio frequency power amplifier wherein reflected power from the load of variable gain power amplification means of which gain varies with an external control voltage is detected by detection means. The reflected output is converted by DC conversion means. Further, the highest voltage is selected from among the converted voltages by selection means. The selected voltage is inputted into a comparator which determines the starting point of the gain control of the variable gain power amplification means. The converted voltage is outputted to control means by switch means, when the converted voltage exceeds a voltage set by the variable gain power amplification means, and this control means controls the gain of the variable gain power amplification means.
Further,
FIG. 5
is a block diagram showing the constitution of a transmitting circuit for a conventional mobile communication equipment or the like.
In
FIG. 5
, a gate voltage
20
is applied to a gate of a final stage amplifier
21
amplifying a radio frequency signal and the output side of the final stage amplifier
21
is connected to an antenna
24
through a directional coupler
22
and an isolator
23
.
Out of two detection outputs of the directional coupler
22
, one detection output is grounded through a terminating resistor
25
, while the other detection output inputs a detection voltage into the positive input terminal of a comparator
27
through a detection diode
26
.
The detection diode
26
detects the output or reflected wave of the final stage amplifier
21
obtained from the directional coupler
22
and converts the detected output or reflected wave into a DC voltage, and the comparator
27
compares this DC voltage with a threshold voltage
28
.
This threshold voltage
28
is applied to the negative input terminal of the comparator
17
. The threshold voltage
28
is determined in advance by the characteristic of a load impedance connected to the output side of the final stage amplifier
21
and the reflected wave which is converted into a DC voltage by the detection diode
26
.
The comparator
27
compares this threshold voltage
28
with the DC voltage of the detection diode
26
, outputs an “H” level or an “L” level depending on whether or not the DC voltage is higher than the threshold voltage
28
, supplies the output to an APC (circuit
29
and allows the APC circuit
29
to control the final stage amplifier
21
.
In such a conventional transmitting circuit, the isolator
23
is inserted into the output side of the final stage amplifier
21
, whereby the load impedance of the final stage amplifier
21
is intended to be stabilized and stable output distortion characteristic and consumption power are ensured.
Due to this, there is no avoiding outputting transmission power including the insertion loss of the isolator from the final amplifier so as to output specified transmission power from the antenna. The conventional transmitting circuit is not, therefore, suited for the reduction of consumption power.
Furthermore, since the isolator is a large component, the isolator is disadvantageously unsuited for miniaturization.
Meanwhile, the reduction of consumption power and the miniaturization of mobile communication equipment are increasingly underway in recent years. In these circumstances, it is demanded to secure the stable output distortion characteristics of a final stage amplifier and consumption power and to realize low power consumption and miniaturization.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a transmitting circuit capable of making a mobile communication equipment small, capable of reducing consumption power and capable of being excellent in the electrical characteristics of a final stage amplifier.
The transmitting circuit of the present invention is characterized by comprising: a final stage amplifier amplifying an inputted radio frequency (RF) signal to a specified transmission output, and capable of controlling consumption power and output distortion by a direct current voltage applied to a gate; a directional coupler having a terminal capable of detecting output power outputted from the final stage amplifier, and a terminal capable of detecting a reflected wave generated by mismatching between an output impedance of the final stage amplifier and a load impedance connected to an output side of the final stage amplifier; two first switches appropriately selecting the terminals of the directional coupler in a time division manner; a terminating resistor provided to correspond to each of the first switches, and terminating the terminal of the directional coupler unselected by the first switches; a detection diode converting each of the output power and the reflected wave obtained by the directional coupler into a direct current voltage; a second switch selecting, switching and outputting one of the direct current voltage with respect to the output power and the direct current voltage with respect to the reflected wave obtained by the detection diode; and gate voltage control means for applying a gate voltage suited for the load impedance to the final stage amplifier in accordance with the direct current voltage with respect to the reflected wave selected by the second switch.
The final stage amplifier amplifies the inputted radio frequency signal to the specified transmission output, the output power of the final stage amplifier is detected by the directional coupler, and the reflected wave generated by the mismatching between the output impedance of the final stage amplifier and the load impedance connected to the output side of the final stage amplifier is detected and supplied to the two first switches.
The first switches are switched in a time division manner, the output power of the final stage amplifier and the reflected wave are selectively applied to the detection diode and detected by the detected diode. By doing so, the output power or the reflected wave is converted into a direct current voltage and applied to the second switch.
If the second switch is switched in a time division manner to select the direct current voltage corresponding to the reflected wave, the gate voltage control means applies a gate voltage suited for the load impedance to the final stage amplifier in accordance with the direct current voltage corresponding to the reflected wave. Thus, it is possible to miniaturize a mobile communication equipment, reduce consumption power and make the final stage amplifier exhibit excellent electrical characteristics.
As stated so far, according to this invention, the reflected wave generated by the mismatching between the output impedance of the final stage amplifier and the load impedance connected to the output of the final stage amplifier is detected, and the gate voltage suited for the load impedance is applied to the gate of the final stage amplifier by the gate voltage control means. As a result, it is possible to dispense with an isolator which is a large-sized component required conventionally, and according to that, specified transmission power may be outputted from the final stage amplifier. Therefore, it is possible to miniaturize a mobile communication equipment small,
McGuireWoods LLP
NEC Corporation
Nguyen Khanh Van
Pascal Robert
LandOfFree
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