A PORTABLE RADIO TRANSCEIVER

Abstract: A portable radio transceiver has a transmitter power amplifier (PA) and a series transistor (V1), which is connected to the transmitter power amplifier and is adapted, in response to a transmission control signal (TX on/off), to control transmission by the transmitter power amplifier. Negative bias generating means provides negative bias (Vneg) to the transmitter power amplifier and is also used for increasing a voltage applied to the gate of the series transistor so as to reduce its resistance. The negative bias generating means has a second transistor (V2) connected to the gate of the series transistor (V1), and a third transistor (V3), the gate of which is adapted to receive the transmission control signal (TX on/off). It also has a capacitor (C1) connected between the second and third transistors, and a diode means (D1) connected between the capacitor and the second transistor.

Description: A PORTABLE RADIO TRANSCEIVER Technical Field The present invention relates to portable radio transceivers, such as mobile telephones. More particularly, the invention is directed at a portable radio transceiver having a transmitter power amplifier, a series transistor, which is connected to the transmitter power amplifier and is adapted, in response to a transmission control signal, to control transmission by the transmitter power amplifier, and negative bias generating means for providing negative bias to the transmitter power amplifier, where the negative bias generating means is also used for increasing a voltage applied to the gate of the series transistor so as to reduce its resistance. Background Art The voltage supply used in portable electronic communication devices, such as mobile telephones, gets lower and lower. Output power amplification is provided by a transmitter power amplifier, which usually comprises GaAs semiconductor components. A negative bias has to be generated and must be applied to the gates of the GaAs compo- nents, before positive supply voltage is applied. Otherwise, very high current peaks may arise and, under unfortunate circumstances, damage the semiconductor components . A series transistor, usually a MOSFET transistor, is connected in series with the supply voltage and the transmitter power amplifier so as to disable and enable transmission by the transmitter power amplifier in response to a transmission control signal on its gate. The series transistor must have as low internal resistance as possible during transmission, so that an unnecessary voltage drop is not generated between the battery and the transmitter power amplifier. It is well- known that the resistance of a MOSFET transistor decreases with increasing voltage between source and gate, once the conduction threshold has been reached. The battery voltage limits the highest possible voltage, that may be applied between source and gate of the series transistor, unless special means are provided. EP-A2-0 700 165 discloses a portable radio transceiver having means in the form of a charge pump for generating a negative bias voltage to a GaAs transmitter power amplifier transistor. A positive voltage supply to the transmitter power amplifier is controlled by a series transistor (p-channel MOSFET) , which is connected in series between the positive voltage supply from the battery and the transmitter power amplifier. The transmitter power amplifier is disabled and enabled in response to a transmit control signal, which is applied to the gate of the series transistor. Moreover, the charge pump for generating negative bias to the transmitter power amplifier is also used for increasing the voltage applied to the gate of the series transistor, by means of a level shifter, so as to reduce the internal resistance of the series transistor. The portable radio transceiver shown in EP-A2-0 700 165 is thus capable of reducing the internal resistance of the series transistor, thereby reducing the voltage drop between battery and transmitter power amplifier. However, the solution shown in this patent publication requires complex circuitry for the charge pump and the level shifter. Summary of the Invention It is an object of the present invention to simplify the circuitry required for providing the negative bias supply and the reduction in internal resistance of the series transistor for a portable radio transceiver according to the above . Another purpose of the present invention is to provide immunity against transmit control signal faults, particularly so that a transmit control signal, which is erroneously maintained at its on- level, will not maintain the transmitter power amplifier in transmit mode during a long period of time. It is a further object of the present invention to provide improved protection for the semiconductor components of the transmitter power amplifier. The above objects are achieved by a portable radio transceiver according to the appended independent patent claim. Other objects, features and advantages of the present invention will appear from the following detailed disclosure, from the drawing as well as from the dependent claims . Brief Description of the Drawings A preferred embodiment of the present invention will now be described in more detail, reference being made to the accompanying drawing, in which FIG 1 illustrates a schematic circuit diagram of the preferred embodiment. Detailed Disclosure FIG 1 illustrates a preferred embodiment of the invention, which comprises voltage-doubling circuitry with high efficiency for controlling the series transistor to disable and enable the transmitter power amplifier. The voltage doubling circuitry is only active during transmit control pulses, wherein power losses are minimized and smaller semiconductors may be used. Only one common control signal from a controller (not shown in the drawing) of the radio transceiver is used for enabling negative bias voltage supply to at least one GaAs semiconductor component of the transmitter power amplifier, as well as positive voltage supply through the series transistor to the transmitter power amplifier. A further advantage is that no supply voltage will reach the transmitter power amplifier, if the bias voltage is not negative enough. Moreover, if a transmit control signal will erroneously remain in its on condition, it will be automatically interrupted, before any damage has occurred. The circuitry of FIG 1 comprises a p-channel MOSFET transistor VI, which in a well-known way may be brought to a conductive and an isolating state, respectively, depending on a voltage applied between gate and source. Moreover, two n-channel MOSFET transistors V2 and V3 are provided in the circuitry and preferably have their transition voltage between 2 and 3 volt . Moreover, a Schottky diode Dl is provided and is conductive in one direction only, having a low voltage drop in its conducting direction and an inverse voltage, which exceeds the maximum supply voltage of the circuitry. In addition, two resistors Rl and R2 are provided, as well as a capacitor Cl . The circuitry shown in FIG 1 has the following operation, assuming that the transmission control signal TX on/off at V3 ' s gate is 0 volt, when voltage in initially supplied to the circuitry. Resistor Rl will then charge capacitor Cl , wherein the voltage at V3 ' s drain will be equal to the supply voltage +V. The diode Dl will prevent the second terminal of Cl , which is connected to the source of the transistor V2 , from becoming more positive than a diode voltage. The voltage across Cl will be the supply voltage minus the diode voltage drop. The transistor V2 will be cut off, when the voltage across gate and source does not reach the conducting voltage at about 2.5 volt. The series transistor VI is cut off, since R2 will keep the gate-source voltage at the same potential. If a voltage exceeding the conducting voltage threshold (> 2.5 volt) is applied at V3 ' s gate, V3 will force the source terminal of transistor V2 , via the capacitor Cl, to the negative value of the supply voltage, which previously were applied across the capacitor. Transistor V2 will begin to conduct, as soon as its source- gate voltage exceeds the conducting voltage threshold at about 2.5 volt, and the negative voltage (relative to ground) reaches the gate terminal of the series transistor VI. The series transistor VI will now be open, until the charge at capacitor Cl has been discharged through V2 by resistor R2 to such an extent, that V2 will again be cut off and consequently also the series transistor VI. Hence, an automatic disabling operation is achieved. By selecting a MOSFET with a suitable pinch-off, the threshold for controlling the negative voltage and thus the disabling and enabling of the supply voltage may be selected. If the control voltage at the gate terminal of transistor V3 changes to 0, before capacitor Cl has been fully discharged through V2 by R2 , resistor Rl will force the voltage at the source terminal of V2 to rise immediately to the conducting voltage drop of the diode Dl . Transistor V2 will block, as soon as the voltage passes the conducting voltage threshold (pinch-off) . Preferably, but not necessarily, the portable radio transceiver described above is a mobile telephone.

Claims: CLAIMS 1. A portable radio transceiver, comprising a trans- mitter power amplifier (PA) , a series transistor (VI) , which is connected to the transmitter power amplifier and is adapted, in response to a transmission control signal (TX on/off) , to control transmission by the transmitter power amplifier, and negative bias generating means for providing negative bias (V neg ) to the transmitter power amplifier, wherein the negative bias generating means is also used for increasing a voltage applied to the gate of the series transistor so as to reduce its resistance, characterized in that the negative bias generating means comprises : a second transistor (V2) connected to the gate of the series transistor (VI) , a third transistor (V3) , the gate of which is adapted to receive said transmission control signal (TX on/off) , a capacitor (Cl) connected between the second and third transistors, and a diode means (Dl) connected between the capacitor and the second transistor. 2. A portable radio transceiver as in claim 1, wherein the negative bias (V neg ) is supplied to the transmitter power amplifier (PA) from a node between the capacitor (Cl) and the second transistor (V2) . 3. A portable radio transceiver as in claim 1 or 2 , wherein the series transistor (VI) is a p-channel MOSFET, whereas the second and third transistors (V2 , V3 ) are n- channel MOSFETs . 4. A portable radio transceiver as in any preceding claim, wherein the transmitter power amplifier (PA) comprises at least one GaAs semiconductor component . 5. A portable radio transceiver as in any preceding claim, in the form of a mobile telephone.

Inventors: KOITSALU EVALD, KOITSALU, EVALD
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 2000
Main classification: H04B1
IPC codes: H03F1, H04B1