Optics: image projectors – Plural projection paths with single light source
Reexamination Certificate
2000-02-02
2001-07-17
Wong, Peter S. (Department: 2838)
Optics: image projectors
Plural projection paths with single light source
C323S205000, C323S286000
Reexamination Certificate
active
06260975
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power control apparatus. More particularly, the present invention relates to an apparatus for automatically adjusting an input signal to a desired power level and outputting the obtained result and to an apparatus suitable for, e.g., a radio transmitter adopting TDMA (Time Division Multiple Access) for carrying out burst transmission.
2. Description of the Background Art
FIG. 19
is a block diagram showing a structure of a conventional power control apparatus, and such an apparatus is disclosed in, for example, Japanese patent laid-open publication No. Hei4-354209. In
FIG. 19
, the power control apparatus is equipped with: a power amplifier
102
; a directional coupler
103
; a transmitting antenna
104
; a cymoscope
105
: direct-current amplifiers
106
and
112
; A/D converters
107
and
115
; a CPU
108
; a PROM
109
; a pulse width modulation generator
110
; a low-pass filter
111
; a temperature detector
113
; and a direct-current converter
114
.
A modulated high-frequency signal is amplified by the power amplifier
102
and divided into power to be supplied to the transmitting antenna
104
and that to be supplied to the cymoscope
105
by the directional coupler
103
. The power supplied to the cymoscope
105
serves as control power for controlling the electric power to be supplied to the transmitting antenna
104
, i.e., an output level of a carrier wave.
The control power is detected by the cymoscope
105
and converted into a direct voltage to be amplified by the direct-current amplifier
106
. The direct-current voltage amplified by the direct-current amplifier
106
is digital-coded by the A/D converter
107
and fetched in the CPU
108
.
Meanwhile, a circuit temperature of the power control apparatus is detected by the temperature detector
113
and supplied to the direct-current converter
114
as a temperature signal. The temperature signal is converted into a direct-current voltage by the direct-current converter
114
and then digitized by the A/D converter
105
to be fetched in the CPU
108
.
The CPU
108
generates an appropriate correction instruction signal associated with the circuit temperature based on the above-mentioned two types of digital input data and correction data stored in an PROM
109
. The correction instruction signal is fed to the PWM generator
110
in which a pulse-width-modulated control voltage is generated. This control voltage is converted into a direct current voltage by the low-pass filter
111
and amplified by the direct-current amplifier
118
. The control voltage amplified.by the direct-current amplifier
118
is supplied to the power amplifier
102
in order to control an output from the power amplifier
102
.
In such a conventional power control apparatus, however, a time constant of the low-pass filter
111
for converting the control voltage into the direct-current voltage is a fixed value determined in accordance with characteristics of the lower-pass filter. The control voltage may discretely vary by an amount or period of renewal of the control voltage and, in this case, the low-pass filter having a fixed time constant has such a problem as that the discrete change in the control voltage can not be sufficiently smoothed to stabilize the control loop.
Further, when a low-pass filter having a large time constant is used as the low-pass filter
111
in order to solve the above-described problem, in the high-speed burst transmission of a radio communication apparatus adopting TDMA for example, the rising of the transmitted power slows down to collapse data in the burst leading edge.
Furthermore, if a change in the ambient temperature or a power supply voltage fluctuation of a circuit is observed, the overshoot or undershoot of the transmitted power is generated immediately after start of transmission and immediately after stop of transmission due to the environmental capability, the bias change and the like of the direct-current amplifier, the power amplifier and others.
SUMMARY OF THE INVENTION
In view of the above-described drawbacks, it is an object of the present invention to provide a power control apparatus capable of optimally controlling a first or last transition characteristic of transmitted power by varying a time constant of a low-pass filter at a first or last transition of the transmitted power.
It is another object of the present invention to provide a power control apparatus capable of setting a time constant of a low-pass filter to an optimal value at a first or last transition of transmitted power even if an operational environment is changed due to a fluctuation of a temperature of the apparatus or of an ambient temperature and the like.
To achieve this aim, according to one aspect of the present invention, the invention provides a power control apparatus comprising: a power level adjusting circuit for adjusting an input signal to a desired power level in accordance with a control voltage and outputting the obtained result; a control voltage generating circuit for comparing a current output power of the power level adjusting circuit with a target power level and generating the control voltage based on a result of comparison; a low-pass filter that operates in accordance with either a first time constant or a second time constant smaller than the first time constant and filters the control voltage generated by the control voltage generating circuit to be supplied to the power level adjusting circuit; and filter controlling means for causing the low-pass filter to operate in accordance with the second time constant at a first transition of the output power from the power level adjusting circuit and causing the low-pass filter to operate in accordance with the first time constant after the first transition of the output power from the power level adjusting circuit.
According to another aspect of the present invention, the invention provides a power control apparatus comprising: a power level adjusting circuit for adjusting an input signal to a desired power level in accordance with a control voltage and outputting the obtained result; a control voltage generating circuit for comparing a current output power of the power level adjusting circuit with a target power level and generating the control voltage based on a result of comparison; a low-pass filter that operates in accordance with either a first time constant or a second time constant smaller than the first time constant and filters the control voltage generated by the control voltage generating circuit to be supplied to the power level adjusting circuit; and filter controlling means for causing the low-pass filter to operate in accordance with the first time constant before a last transition of the output power from the power level adjusting circuit and causing the low-pass filter to operate in accordance with the second time constant at the last transition of the output power from the power level adjusting circuit.
According to a further aspect of the present invention, the invention provides a power control apparatus comprising: a power level adjusting circuit for adjusting an input signal to a desired power level in accordance with a control voltage and outputting the obtained result; a control voltage generating circuit for comparing a current output power of the power level adjusting circuit with a target power level and generating the control voltage based on a result of comparison; a low-pass filter that operates in accordance with either a first time constant or a second time constant smaller than the first time constant and filters the control voltage generated by the control voltage generating circuit to be supplied to the power level adjusting circuit; and filter controlling means for causing the low-pass filter to operate in accordance with the second time constant at a first transition of the output power from the power level adjusting circuit, causing the low-pass filter to operate in accordance with the first time constant after the first tra
Laxton Gary L.
Mitsubishi Denki & Kabushiki Kaisha
Rothwell Figg Ernst & Manbeck
Wong Peter S.
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