Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2000-12-28
2002-04-09
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S513000, C455S126000, C330S140000
Reexamination Certificate
active
06369635
ABSTRACT:
BACKGROUND
The invention concerns a temperature-compensated diode rectifier for an HF level controller, which is located in the gain control loop of an HF amplifier to control the output level of an HF transmitter. The controlled HF amplifier is preferably arranged at the output of a radio telephone modulator. In particular, this is a cellular telephone designed to operate in different transmission bands. The object of the control circuit is to keep the transmitting power of the radio telephone's antenna constant at a set value within a large power range and over a large operating temperature range.
During the telephone operation, radio telephones like cellular telephones adjust their HF transmitting power as a function of the base station density in a radio network and the momentary transmission conditions. After the radio telephone accesses the radio network, the latter assigns a transmission channel to the telephone and continuously monitors the transmission quality. In addition to other HF parameters such as channel frequency and time slot position, the level of the HF transmitting power must be maintained relatively precisely. Rural areas with a low number of simultaneous telephone connections generally have a low base station density despite the advanced development of the radio networks, so that a radio path of up to 40 km to the next base station and poor propagation conditions require the maximum available transmitting power of about 33 dBm (=2 Watt). In contrast thereto, dense population and a high base station density leads to short radio paths which are often only 100 meters long. The transmitting power in such short radio paths can often be reduced to a few dBm/mW to reduce battery load and ensure the transmission quality.
In addition, with high transmitting power and low cell size common channel disturbances can occur in other cells if in accordance with the applicable conventions both cells occupy the same channel. On the other hand, transmitting power which is too low leads to insufficient transmission quality.
It can therefore be seen that on the one hand the control circuit must adjust the HF transmitting power of a cellular telephone as precisely as possible and in a reproducible manner in accordance with the transmission conditions in a large dynamic range, and on the other hand it must maintain the set value in a wide range of operating temperatures. These requirements are difficult to fulfill with low HF transmitting power.
According to the present state of development, the transmitting power including power losses in the cellular telephone, for example in the transmitting/receiving switch, must be adjustable for a 900 MHz frequency band in a range of levels between 5 dBm and 39 dBm, and for the frequency bands of 1800 MHz and 1900 MHz in a range between 0 dBm and 36 dBm. These settings should have an accuracy of ±0.5 dBm in the temperature range of −20° C. to +60° C.
The present invention starts with a temperature-compensated diode rectifier circuit according to application EP 0 834 987 A2. To better understand the problem, differences between the known solution and the present invention are explained by means of FIG.
1
.
An HF amplifier PA is located between the modulator output of a not illustrated telephone module and an antenna circuit A, to amplify a transmission signal RF
IN
which in this case is digitally modulated to 900 MHz on a carrier. To obtain an HF output signal RF
OUT
for the antenna circuit A at a defined power level in the above cited level range, a control loop with a comparator COM which compares the known desired value to the actual value, adjusts the amplification of the HF amplifier PA. The comparator COM compares a d.c. control voltage U
CTR
, which corresponds to the desired power level, with a rectified voltage U
D
whose level depends on the power level of the HF output signal RF
OUT
. A rectifier circuit with a rectifier diode D
1
, a charging capacitor C
1
and a ballast resistor R
2
obtains the rectified voltage U
D
from the output signal RF
OUT
of the antenna circuit. A directional coupler D-CO connects the rectifier circuit to the antenna circuit.
The voltage of the HF output signal RF
OUT
in the cited level range varies by more than the ratio n=1:30. This requires a linear conducting characteristic of the rectifier diode and a steep transition from the off mode to the conducting mode, in order to obtain a small setting deviation even at low levels. This is made more difficult because in extreme cases only a minimum 3 V operating voltage is available for a cellular telephone. Since the comparator COM can only compare voltages which are below its own operating voltage, the directional coupler D-CO and the rectifier circuit must be designed so that even at a maximum power level the rectified voltage U
D
is still at least slightly under this value. The result is that even with an ideal characteristic diode curve, the part of the rectified output signal Û
RF
at the lowest power level in the rectified voltage U
D
would be under 100 mV.
The transition from the off mode to the conducting mode in rectifier diodes lies outside of the axial zero point. Without special measures only one rectified voltage U
D
reaches the output when the amplitude of the decoupled output signal is above a threshold voltage U
T
. For that reason the diode D
1
operates advantageously with a bias voltage, or like the solution of application EP 0 834 987 A2 with a bias current. The threshold voltage U
T
depends on the operating temperature and in Schottky diodes for example it is in the desired temperature range under U
T
=300 mV.
The power level at the output of the HF amplifier PA must be independent of operating temperature changes. However this is not so in conventional rectifier circuits. Conventional diodes with small forward currents have a temperature dependence of about 2.0 mV/° C. Thus a permissible 80° C. temperature change requires a change of 160 mV in the rectified voltage U
D
. This is larger than the part of rectified the output signal Û
RF
in the voltage.
To compensate the temperature run of the rectified voltage U
R
, it is known from application EP 0 834 987 A2 to place a compensating diode D
2
in series with the ballast resistor R
2
, and to connect one side of the rectifier diode D
1
to the battery voltage U
BAT
via a ballast resistor R
1
. This creates a voltage divider for the battery voltage U
BAT
with a series circuit of a diode D
1
or D
2
and a resistor R
1
or R
2
in each dividing branch, and the rectifier output O
R
has the rectified voltage U
D
=U
DO
+Û
RF
which contains a bias component U
DO
=U
T
+Û
R2
. With a bias current I
BIAS
between 20 &mgr;A and 200 &mgr;A, the battery voltage Û
BAT
places both diodes D
1
, D
2
in the conductive condition. Due to the temperature dependence of diodes D
1
and D
2
, the bias current I
BIAS
is also temperature dependent. However since equal diode types and thermally coupled diodes D
1
, D
2
have the same temperature dependence in each dividing branch, the division ratio of the voltage divider remains stable insofar as the dropping resistor R
1
and the ballast resistor R
2
have the same value and the comparator COM has a high input resistance. In this case the bias component U
DO
=1/2 U
BAT
and only depends on the battery voltage U
BAT
level. The rectified voltage U
M
can therefore only vary between full and half the operating voltage value. In practice this reduces the variation range of the rectified output signal Û
RF
in the rectified voltage U
D
to 1.5 Volts. However if the resistors R
1
and R
2
are different, for example to expand the variation range of the rectified voltage U
D
, the rectifier circuit has a defined temperature run. The ratio of the resistors to each other can be used to establish a positive or a negative temperature run. The decoupled output signal goes from the directional coupler D-CO via a coupling capacitor C
2
to a summation point S in the rectifier ci
Fritzmann Martin
Weiss Manfred
Nokia Mobile Phones Ltd.
Tra Quani
Tran Toan
LandOfFree
Temperature-compensated diode rectifier circuit for an HF... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Temperature-compensated diode rectifier circuit for an HF..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Temperature-compensated diode rectifier circuit for an HF... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2889411