Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
1998-05-21
2001-10-09
Bost, Dwayne (Department: 2681)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S073000, C455S086000, C455S522000, C455S069000, C330S051000
Reexamination Certificate
active
06301467
ABSTRACT:
FIELD OF THE INVENTION
The invention relates in general to the selection of mutually alternative circuits by means of an electric signal. In particular the invention relates to the selection cf parallel amplifiers such that all of them are not simultaneously in use.
BACKGROUND ART
In many signal processing applications, signals must be offered in various situations alternative routes through active components. An exemplary case is provided by a radio transmitter's power amplifier arranged so as to operate at different power levels according to need. It is known that the transmission power of a mobile phone, for example, varies in accordance with the magnitude of the power needed to establish a functional and error-free uplink connection between the mobile phone and a base station. The efficiency of individual radio-frequency amplifiers varies as a function of the output power so that the amplifier is usually the most efficient at high output power values. When such a radio-frequency amplifier operates at a lower power, the efficiency is poor and electric power is wasted.
To save the batteries of portable radio apparatuses the consumption of electricity in all parts of the apparatuses should be minimal in all situations, wherefore different solutions have been developed to improve the efficiency of the amplifiers at low power levels. A known solution is to place in the power amplifier of a transmitter, instead of a single radio-frequency amplifier, two or more parallel amplifiers optimised to different power levels. The outputs of the parallel amplifiers are connected to a selection switch to select the amplifier which is closest to optimum for the current power level. In the GSM (Global System for Mobile Telecommunications), for instance, the selection is carried out as follows: the base stations measure the strengths of the signals received from mobile terminals and send out commands lo the terminals, instructing the terminals to adjust the transmission power. When a received signal becomes weaker, the base station instructs the terminal to increase the transmission power or hand over the connection to another base station. If a received signal is so strong that the transmission power of the terminal can be decreased without compromising signal quality, the base station instructs the terminal to decrease the transmission power. In the GSM system, the transmission power of a hand phone may typically vary from 1 mW to 2 W (in the dBm scale, from 0 dBm to +33 dBm).
It can be considered a disadvantage of prior-art solutions that a selection switch connected in series with parallel amplifiers has to be capable of withstanding the maximum output power of the amplifier with the highest power so that the switch easily becomes rather large in size and expensive to manufacture. In addition, a selection switch connected in series on the path of the signal causes losses, which is in contradiction with the power-saving goals of the arrangement. Switch arrangements cause unnecessary losses also in other cases where the signal has to be directed to pass through at least two mutually alternative active components. An, example of such a switch arrangement is an antenna switch of a radio apparatus based on time division duplex, TDD, which couples to the antenna of the radic apparatus either the power amplifier output of the transmitter or the low-noise preamplifier input of the receiver.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and circuit arrangement with which the course of a signal can be controlled in mutually alternative active components with smaller losses than in the arrangements according to the prior art. Another object of the invention is to provide a method and circuit arrangement with which the above-mentioned object is achieved with low manufacturing costs and using small-sized components.
The objects of the invention are achieved by selectively setting the active components into active or inactive state by means of voltage signals brought to themrr so that an active component in inactive state presents high impedance which has no significant effect on the propagation of the signal.
The circuit arrangement according to the invention to control the course of arm oscillating signal in mutually alternative first active component and second active component, both of which can be set into active state by a certain first value of a control signal brought to the component and which are set into inactive state by a certain second value of said control signal, is characterised in that it comprise, means for setting said active components selectively into active state so that the first active component can be set into active state by a control signal brought to it while the second active component is in inactive state, and the second active component can be set into active state by a control signal brought to it while the first active component is in inactive state.
The invention is also directed to a communications device employing the circuit arrangement mentioned above. The communications device according to the invention is characterised in that it comprises means for selectively setting alternative active components included in it into active state so that a first active component can be set into active state by a control signal brought to it while a second active component is in inactive state, and the second active component can be set into active state by a control signal brought to it while the first active component is in inactive state.
The invention is further directed to a method which is characterised in that a signal is directed to travel via a first active component by setting it into active state by means of a control signal brought to it and simultaneously essentially preventing a second active component from influencing the course of the signal.
It is typical of active components, such as transistors, that the impedance. represented by their electrodes in the circuit to which they are connected depends on the biasing of the active component. For example, the output impedance of a transistor amplifier in active state differs from the output impedance of a transistor amplifier in inactive state. In the case of parallel transistor amplifiers the invention means that their outputs are interconnected in the manner described later on so that the output impedance of the unbiased (inactive) transistors is utilised as part of the amplifier block output matching circuit. Parallel with the output of an active transistor, the inactive transistors look like high-impedance circuits which have very little effect on the operation of the active transistor or on the flow of the signal from the output of the active transistor toward an antenna or other destination. For practical considerations the inactive transistors may be treated as not affecting the signal at all.
The invention is not confined to the selection of parallel codirectional amplifiers. Of a transmitter amplifier output and receiver amplifier input connected to an antenna, for example, one can be made by means of biasing to seem to a signal as a high-impedance circuit so that the biasing replaces a separate antenna switch.
A selection switch that selectively couples different bias voltages can be rated for a considerably lower maximum power than a prior-art selection switch connected in series with the amplifiers, whereby the circuit arrangement according to the invention is smaller in size and has lower manufacturing costs than solutions according to the prior art. In addition, the invention eliminates unnecessary switch components connected in series on the path of the signal, thus reducing losses and further improving the efficiency of the circuit arrangement. In addition to literally setting the bias voltages, the same biasing effect may be achieved by affecting the operating voltages of the parallel active components in a way described in more detailed fashion later.
REFERENCES:
patent: 5054114 (1991-10-01), Erickson
patent: 5091919 (1992-02-01), Kuisma
patent: 5123
Jarvinen Esko
Varis Jukka
Bost Dwayne
Contee Joy K.
Nokia Mobile Phones Ltd.
Perman & Green LLP
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