Telecommunications – Transmitter – Measuring – testing – or monitoring of transmitter
Reexamination Certificate
2000-02-03
2003-12-23
Vo, Nguyen T. (Department: 2681)
Telecommunications
Transmitter
Measuring, testing, or monitoring of transmitter
C455S126000, C455S127100, C455S127200, C455S116000, C330S289000, C330S278000, C330S279000
Reexamination Certificate
active
06668162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The object of the invention is to compensate the temperature drift of a detector and a control signal, in other words to compensate the offset caused by the temperature change, in a periodic control action in order to reduce the variation caused to the controlled phenomenon, particularly in a mobile station such as a mobile phone.
2. Description of Related Art
Such periodic control actions are at least the Automatic Gain Control (AGC) and the transmission power control. Such a controlled phenomenon is generally the power of an RF (radio frequency) signal. At the control moment the control signal sets the desired control result, such as the power of the signal to be amplified. The temperature drift of the detector is at least partly due to a change in the threshold voltage of the diode, and the temperature drift of the control signal is at least partly due to a change in the output voltage of the digital-to-analogue converter. Further errors can be caused by a changed dependence between the inputs of the differential amplifier.
A problem in low-power applications is particularly the temperature drift on one hand of the detector diode in a detector indicating the magnitude of the power, such as a diode detector, and on the other hand of the power control signal. For instance, the temperature drift of a simple diode detector is typically 2 mV/° C. The detector receives a signal with an amplitude, which as a minimum can be only a few millivolts. When the width of the temperature range is for instance 100° C. it causes temperature drift which is many times higher than a signal with a small amplitude. In order to reduce the temperature drift it is known to compensate a diode detector according to
FIG. 1A
with a second diode. The compensation is made in the block B
1
by a circuitry after the capacitor C
1
which connects the RF signal. The circuitry includes an ordinary pull-up resistor R
1
C and a pull-down resistor R
2
C, a compensating diode D
1
C connected between the resistors in the forward direction, and a capacitor C
1
C connected in parallel with the compensating diode D
1
C and the pull-down resistor R
2
C, whereby the signal line is connected through the resistor R
3
C to the operating voltage side of the compensating diode. The temperature changes which act on the compensating diode D
1
C are the same or almost the same as those which act on the detector diode D
1
which connects the positive half-periods of the RF signal supplied by the capacitor C
1
to the integrating capacitor C
2
and the load resistor R
3
. The circuitry is designed so that changes in the characteristics of the compensating diode D
1
and the detector diode D
1
will cancel each other, so that no temperature drift will occur. The voltage V
DET
supplied to the terminal RF
IN
which corresponds to the power of the RF signal is obtained at the integrating capacitor C
2
and the load resistor R
3
.
The circuitry according to
FIG. 1A
reduces the temperature drift, but the currents with different magnitudes passing through the compensating diode D
1
C and the detector diode D
1
will not enable a complete compensation of the temperature drift. Further the realisation of this circuitry requires many components.
There is also a known detector of periodic power according to
FIG. 1B
which prevents temperature drift and has a power detector B
2
based on a diode D
1
, an amplifier B
3
, and a sampling circuit B
4
. The power detector B
2
operates as follows: an RF signal is connected to the input RF
IN
and further to the capacitor C
1
, from where the transferred signal acts, via the connection point of the resistance bridge R
1
, R
2
between the operating voltage and the ground and through the diode D
1
, on the capacitor C
2
which can be charged with a positive potential and on a corresponding discharging resistor R
3
, whereby a voltage level corresponding to the power is supplied to the switch S
1
. The amplifier B
3
operates as follows: in the OFF position the switch S
1
switches the reference voltage to the capacitor C
3
when no RF signal is transmitted or supplied to the periodic power detector; during signal reception the switch S
1
is connected to the ON position, whereby the signal is connected via the resistor R
4
to the amplifier A
1
having a feedback via the resistor R
5
. The output of the amplifier A
1
provides at the point OUT
1
a power detection result which is proportional to the difference of the idle state power and the transmitted power, and this detection result is further supplied to the sampling circuit B
4
. The sampling circuit B
4
operates as follows: at the sampling moment the switch S
2
directs the output voltage OUT
1
of the amplifier A
1
to the capacitor C
4
, and the voltage of the capacitor is repeated by the amplifier A
2
to the point OUT
2
. A power detector of this kind is used to correct the control of the transmit power of the transmitter.
The circuit according to
FIG. 1B
will effectively reduce the temperature drift.
A problem in known detectors and controllers is the mutually independent temperature drifts of on one hand the output signal of the detectors used to generate the gain control voltage and on the other hand the control signal setting the magnitude of the gain. The circuitries presented above reduce the temperature drift of the power detector. Typically the control signal is generated by a digital-to-analogue converter having a temperature drift corresponding to the residual temperature drift of the compensated diode detector according to FIG.
1
A.
SUMMARY OF THE INVENTION
The object of the invention is to present a control based on a detector and a control signal, so that the control compensates the drift of the output signal of the detector and of the control signal caused for example by temperature variations.
The invention relates to a method for reducing the effects of drift of a detector of transmitted power and of a transmission power control signal in a transmitter arranged to transmit in an intermittent fashion, the output signal from the detector and the control signal controlling at least in part the transmission power of the transmitter. According to the invention, the method comprises at least the steps of storing of a voltage difference between the output voltage of the detector and the control signal during a pause in transmission, and using said stored voltage difference for compensating the drift of the detector and the control signal during a transmission period. The invention also relates to a system for compensating drifts in a transmitter arranged to transmit in an intermittent fashion, the transmitter having at least a detector of transmitted power and a control signal line for controlling the transmitted power. According to the invention the system comprises at least means for storing the voltage difference between the output voltage of the detector and the control voltage in the control signal line during a pause in transmission, and means for compensating the drift of the detector and the control signal during a transmission period using a stored voltage difference stored by said means for storing.
According to a further advantageous embodiment of the invention the system further comprises a compensation and control block for the compensation of the temperature drift of the detection and of the control signal. In a still further embodiment of the invention the compensation and control block further comprises the compensation of the temperature drift of the differential amplifier.
According to a further advantageous embodiment of the invention a system for reducing the effect of the temperature drift of a detector and of a control signal and for compensating the effect of the bias voltage variation in a diode detector is provided, which system comprises a diode detector for detecting the transmit power of an RF time division signal. According to the invention the effect of the bias voltage variations of the diode detector is compensated in the transmit pow
Nguyen Huy
Nokia Mobile Phones Ltd.
Vo Nguyen T.
LandOfFree
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