Amplifier for radio transmission

In a radio transmission amplifier unit which has between input and output terminals a gain-controlled amplifier 11, a pre-amplifier 12 connected to the output thereof and a main amplifier 13 supplied with the output therefrom, the range of the transmitting power level is divided into small, medium and large regions. In the small transmitting power level region, the power supply to the pre- and main amplifiers is cut off by power-supply switches 28 and 29 and the output of the gain-controlled amplifier 11 is connected to a terminal 14 via switches 15, 18 and 19; in the medium transmitting power level region, the power-supply switch 28 is turned ON and the switch 29 OFF to connect the switch 15 to the pre-amplifier and the output of the pre-amplifier is connected to the terminal 14 via switches 21 and 19; and in the large transmitting power level region, the power-supply switches 28 and 29 are turned ON to connect the switch 15 to the pre-amplifier, a switch 16 is connected to the main amplifier, and the output of the main amplifier is connected to the terminal 14 via the switch 19.

TECHNICAL FIELD
 The present invention relates to a radio transmission amplifier unit for
 use, for instance, in a mobile communication system that requires
 substantial control of the transmitting power from each mobile station.
 PRIOR ART
 For example, in a CDMA-based mobile communication system the base station
 sends a transmitting power control signal to respective mobile stations to
 control their transmitting powers so as to make the receiving levels of
 transmitting waves from any mobile stations substantially constant
 regardless of the distances between the mobile stations and the base
 station, thereby reducing interference that is attributable to the
 difference in receiving level among channels assigned with different
 spreading codes.
 In FIG. 1A there is depicted a conventional radio transmission amplifier
 unit that forms part of a radio transmitter of a mobile station. The radio
 transmission amplifier unit has a variable gain-controlled amplifier (GCA)
 11, a pre-amplifier 12 and a main amplifier 13. An input signal from an
 input terminal 10 is amplified by GCA 11, then its output is amplified by
 the pre-amplifier 12, and the amplified output is further amplified by the
 main amplifier 13 having a gain larger than that of the pre-amplifier 12,
 thereafter being provided to an output terminal 14. Though different
 according to its kind, the mobile station performs transmission, for
 example, with a maximum rated transmitting power of 0.3 W, normally, tens
 of milliwatts or so, for instance. Upon each reception of a
 transmitting-power-increase control signal from the base station, the
 mobile station controls GCA 11 to increase the transmitting power by a
 predetermined gain (dB), whereas, upon each reception of a
 transmitting-power-decrease control signal, it controls GCA 11 to decrease
 the transmitting power by a predetermined gain (dB).
 FIG. 1B shows, by way of example, an increase in the transmitting power
 controlling degree and variations in the operation efficiency of such a
 radio transmission amplifier unit by repeated reception of the
 transmitting-power-increase control signal. The conventional radio
 transmission amplifier unit is so designed as to provide maximum
 efficiency when the transmitting power is at the maximum as shown in FIG.
 1B. Consequently, when the transmitting power is low, the operation
 efficiency considerably decreases, resulting in a waste of power. This is
 particularly detrimental to a mobile station that uses a battery as the
 power supply as in the case of a portable telephone.
 An object of the present invention is to provide a radio transmission
 amplifier unit which retains high efficiency even during its operation
 with a transmitting power smaller than the rating.
 DISCLOSURE OF THE INVENTION
 According to a first aspect of the present invention, a radio transmission
 amplifier unit, which amplifies a signal fed to an input terminal and
 provides it to an output terminal, is constructed to comprise:
 a plurality of amplifiers provided between said input terminal and said
 output terminal and each having a power-supply terminal;
 power supply means for supplying power to said plurality of amplifiers;
 power-supply switching means for selectively connecting said power supply
 means to the power-supply terminals of said plurality of amplifiers to
 supply thereto power;
 route switching means for switching the cascade connection of said
 plurality of amplifiers to connect the output of a selected one of said
 amplifiers to said output terminal; and
 control signal generating means for generating switch control signals which
 specify the states of connection by said power-supply switching means and
 said route switching means in accordance with a transmitting power
 controlling degree corresponding to the transmitting power level and for
 applying said switch control signals to said power-supply switching means
 and said route switching means, respectively.
 The radio transmission amplifier unit according to said first aspect of the
 invention may also be constructed so that first and second bias voltages
 are selectively supplied by a bias select switching means from said power
 supply means to the input sides of said plurality of amplifiers.
 According to a second aspect of the present invention, a radio transmission
 amplifier unit, which amplifies a signal fed to an input terminal and
 provides it to an output terminal, is constructed to comprise:
 a plurality of amplifiers connected in cascade between said input terminal
 and said output terminal, each amplifier having a power supply terminal;
 power supply means for outputting at least first and second bias voltages;
 bias select switching means for selectively applying either one of said
 first and second bias voltages to the input sides of said plurality of
 amplifiers to thereby selectively set their operating points; and
 control signal generating means for generating a bias control signal which
 controls the selection of said bias select switching means in
 correspondence to the transmitting power level.

BEST MODE FOR CARRYING OUT THE INVENTION
 In FIG. 2A there are depicted amplifiers 11, 12 and 13 and switches 15, 16,
 18, 19, 21 and 22 for selectively switching them in or out of a signal
 path in a first embodiment of the radio transmission amplifier unit
 according to the present invention, the parts corresponding to those in
 FIG. 1A being identified by the same reference numerals. The switch 15 is
 connected in series between the output end 11.sub.ou of the
 gain-controlled amplifier 11 and the input end 12.sub.in of the
 pre-amplifier 12, and the switch 16 is connected in series between the
 output end 12.sub.ou of the pre-amplifier 12 and the input end 13.sub.in
 of the main amplifier 13. Provision is made for connecting a selected one
 of the output ends 11.sub.ou, 12.sub.ou and 13.sub.ou of the amplifiers
 11, 12 and 13 by select switching means to the output terminal 14. To this
 end, in the illustrated embodiment the switch 15 is formed by a
 change-over switch, which has its movable contact connected to the output
 end 11.sub.ou, its one fixed contact 15a connected to the input end
 12.sub.in and its other fixed contact 15b connected via a switch 18 to one
 fixed contact 19a of a change-over switch 19, which, in turn, has its
 movable contact connected to the output terminal 14 and its other fixed
 contact 19b connected to the output end 13.sub.ou. Further, the output end
 12.sub.ou is connected via a switch 21 to the fixed contact 19a.
 When connecting the change-over switch 15 to the fixed contact 15b and
 turning ON the switch 18 while connecting the change-over switch 19 to the
 fixed contact 19a, the output end 11.sub.ou is connected to the output
 terminal 14; then, when changing over the switch 15 to the fixed contact
 15a and turning ON the switch 21, the output end 12.sub.ou is connected to
 the output terminal 14; and when connecting the change-over switch 19 to
 the fixed contact 19b and turning ON the switch 16, the output end
 13.sub.ou is connected to the output terminal 14. That is, the switches
 15, 18, 19 and 21 constitute select switch means.
 Furthermore, the example of FIG. 2A is adapted so that the fixed contact
 15b of the change-over switch 15 can be connected via the switch 22 to the
 input end 13.sub.in ofthe main amplifier 13 to connect thereto the output
 end 11.sub.ou of the gain-controlled amplifier 11 so as to bypass the
 pre-amplifier 12. Hence, by connecting the change-over switch 15 to the
 fixed contact 15b, then turning OFF the switch 16 and ON the switch 22,
 and connecting the change-over switch 19 to the fixed contact 19b, the
 output from the gain-controlled amplifier 11 bypasses the pre-amplifier 12
 and is fed to the main amplifier 13, thereafter being amplified and then
 provided to the output terminal 14. The switches 15, 16 and 22 constitute
 bypass switch means.
 That is, letting the input terminal 10 be represented by A, the connection
 point of the amplifiers 11 and 12 by B, the connection point of the
 amplifiers 12 and 13 by C, the output terminal 14 by D, the route that
 bypasses the pre-amplifier 12 by B-E-F-C and the route that bypasses the
 main amplifier 13 by C-F-G-D as depicted in FIG. 2B, the amplifier unit of
 FIG. 2A can take any one of routes A-B-C-D, A-B-C-F-G-D and A-B-E-F-G-D.
 However, if the pre- and main amplifiers 12 and 13 have not so much
 different characteristics, there will be no large difference between
 characteristics of the routes which bypass the pre- and main amplifiers 12
 and 13, respectively; therefore, there is no practical need for bypassing
 the pre-amplifier 12. In such an instance, the switch 22 is not provided
 and the switch 18 is normally held ON, i.e. connected. Accordingly, the
 amplifier unit has three selectable states of use, that is, a state in
 which only the amplifier 11 is made active, a state in which the
 amplifiers 11 and 12 are made active, and a state in which the amplifiers
 11, 12 and 13 are all made active. On the contrary, when the
 characteristics of the pre- and main amplifiers 12 and 13 greatly differ,
 the switches 18 and 22 are provided, making it possible to bypass the
 pre-amplifier 12. In this case, a state in which the amplifiers 11 and 13
 are made active is added to the abovementioned three states of use; namely
 a total of four states of use are selectable. The following description
 will be given of the case of selecting from the former three states of
 use.
 In the present invention, the transmitting power controlling degree is
 divided into three regions, i.e. small, medium and large regions (I), (II)
 and (III) corresponding to the three amplifiers 11, 12 and 13,
 respectively, as depicted in FIG. 3A; in the small transmitting power
 controlling region (I) the switch 15 in FIG. 2A is connected to the
 terminal 15b, the switch 18 is turned ON, the switch 19 is connected to
 the terminal 19a, and the switches 21 and 22 are turned OFF, whereby the
 route A-B-E-F-G-D in FIG. 2B is formed. As a result, only the
 gain-controlled amplifier 11 is actuated and the power supply to the pre-
 and main amplifiers 12 and 13 is turned OFF. Accordingly, in this region
 (I) the gain between the route points B and D is 0 dB, and the
 transmitting power in FIG. 3A is determined only by the gain of the
 gain-controlled amplifier 11 depicted in FIG. 3C.
 In the medium transmitting power control variable region (II), the switch
 15 in FIG. 2A is connected to the terminal 15a, the switches 16, 18 and 22
 are turned OFF, the switch 19 is connected to the terminal 19a and the
 switch 21 is turned ON, whereby the route A-B-C-F-G-D is formed. As a
 result, the amplifiers 11 and 12 are made active and the power supply to
 the amplifier 13 is turned OFF. Accordingly, in this region (II) the gain
 between the route points B and D becomes a constant gain by the
 pre-amplifier 12, and by changing the gain of the gain-controlled
 amplifier 11 as shown in the region (II) in FIG. 3C, the output
 characteristic in the medium region (II) depicted in FIG. 3A is obtained.
 At the instant of switching from the region (I) to the region (II) the
 gain of GCA 11 is reduced by the gain G.sub.1 of the amplifier 12 that is
 added in the region (II), by which the transmitting power characteristic
 in FIG. 3A can be made to continue from the region (I) to the region (II).
 In the large transmitting power controlling region (III) the switch 15 in
 FIG. 2A is connected to the terminal 15a, the switch 16 is turned ON, the
 switch 19 is connected to the terminal 19b and the switches 21 and 22 are
 turned OFF, whereby the route A-B-C-D is formed. As a result, all the
 amplifiers 11, 12 and 13 are made active. Accordingly, the gain between
 the route points B and D in this region becomes a constant gain that is
 determined by the sum of the gains of the amplifiers 12 and 13 as depicted
 in FIG. 3B; by changing the gain of the gain-controlled amplifier 11 as
 shown in the region (III) in FIG. 3C, the output characteristic in the
 region (III) in FIG. 3A is obtained. At the instant of switching from the
 region (II) to the region (III), the gain of the gain-controlled amplifier
 11 is reduced by the gain G.sub.2 of the amplifier 13 that is added in the
 region (II), the transmitting power characteristic in FIG. 3A can be made
 to continue from the region (II) to the region (III).
 The efficiency of the radio transmission amplifier unit in the three
 regions (I), (II) and (III) is such as depicted in the corresponding
 regions in FIG. 3D; in the small output region (I) the power supply to the
 amplifiers 12 and 13 is held OFF and in the medium output region (II) the
 power supply to the amplifier 13 is held OFF--this reduces power
 consumption in either region and enhances the efficiency of the radio
 transmission amplifier unit as compared with that in the past.
 To implement such control, a control signal generator 25 formed, for
 example, a memory, is provided as depicted in FIG. 4; the control ranges
 of the transmitting power controlling degree shown in FIG. 3A are made to
 correspond to address values 0 through 255 of the memory 25; there are
 prestored at each address a preset gain of the gain-controlled amplifier
 11 for the corresponding transmitting power controlling degree and
 connection control signals for the switches 15, 16, 18, 19, 21, 22, 28 and
 29 in the region (I), (II), or (III) to which the transmitting power
 controlling degree belongs. There is provided an up-down counter 24 that
 counts up or down upon each application thereto of the output increase or
 decrease control signal. The count value of the up-down counter is used as
 an address corresponding to the transmitting power controlling degree to
 access the memory (control signal generator) 25, from which are read out a
 gain value control signal 32 for setting the corresponding gain in the
 gain-controlled amplifier 11, a switching control signal group 26 for
 controlling the switches 15, 16, 18, 19, 21 and 22, and an amplifier
 ON/OFF signal group 31 for making the pre- and main amplifiers 12 and 13
 operative or inoperative, that is, for effect ON-OFF control of
 power-supply switches 28 and 29 inserted between a battery 27 and
 operating power-supply terminals 12D and 13D of the pre- and main
 amplifiers 12 and 13, respectively. In response to these switching control
 signals the respective switched are turned ON and OFF to effect ON/OFF
 control of the power supply to the amplifiers 12 and 13, and the gain for
 the gain-controlled amplifier 11 is set.
 That is, as shown in FIG. 5, the control signal generator 25 has prestored,
 for example, in its area of the address 255 corresponding to the maximum
 transmitting power controlling degree in the region (III) a switching
 control signal group for controlling the respective switches to choose the
 route A-B-C-D in FIG. 2B, an amplifier ON/OFF signal for turning ON the
 power supply to the main amplifier 13 and turning ON the pre-amplifier 12,
 and a gain control signal that maximizes the gain of the gain-controlled
 amplifier 11 within a variable range. In the area of the address 0
 corresponding to the minimum transmitting power controlling degree in the
 region (I), there are stored a switching control signal group for
 controlling the respective switches to choose the route A-B-E-F-G, a
 signal for turning OFF the operating power supply to the pre- and main
 amplifiers 12 and 13, and a gain control signal that minimizes the gain of
 the gain-controlled amplifier 11 within the variable range.
 Simply by setting the required transmitting power controlling degree as an
 address in the control signal generator 25 as described above, it is
 possible to effect complex switching control of the switches 15, 16, 18,
 19, 21 and 22, ON/OFF control of the power-supply switches 28 and 29 and
 the setting of the gain for the gain-controlled amplifier 11.
 Either of the pre- and main amplifiers 12 and 13 can be formed by such an
 FET amplifier as depicted in FIG. 6A. An input from an input terminal 41
 is fed via a matching circuit 42 to the gate of an FET 43, the source of
 the FET 43 is grounded, and an amplified signal is provided from its drain
 is provided via a matching circuit 44 to an output terminal 45. A drain
 bias V.sub.d is applied via a high-frequency cut-off coil 46 to the drain
 of the FET 43, and a gate bias (input-side bias) V.sub.g is applied via a
 high-frequency cut-off coil 47 to the gate.
 As shown in FIG. 10A, according to an ordinary amplifier biasing method, an
 operating point a on a load line A is determined with respect to the
 maximum permissible input to the amplifier in its drain current
 characteristic. The load curve A is given by the gate bias V.sub.g
 =E.sub.a. With this bias V.sub.g =E.sub.a, the maximum drain current is
 I.sub.amax, and by selecting the operating point a such that the drain
 current I.sub.a =I.sub.amax /2, it is possible to maximize the input level
 that can be amplified substantially linearly. However, since the drain
 current I.sub.a at the operating point a always flows even during the
 no-input period, the operation efficiency of the amplifier decreases
 accordingly. Then, when the input signal is small in level, if the
 operating point is shifted to b by setting the gate bias voltage V.sub.g
 at V.sub.g =E.sub.b that is smaller than E.sub.a as indicated by the curve
 B in FIG. 10A, the drain current I.sub.b can be made small when no input
 is applied or when the input signal level is low; hence, it is possible to
 improve the operation efficiency of the amplifier. By using this method to
 lower the gate bias V.sub.g of each of the amplifiers 12 and/or 13
 supplied with power in the regions (II) and/or (III) described previously,
 for example, in respect of FIGS. 3A through 3D, the operating point is
 shifted to the point b on the load curve B, by which it is possible to
 suppress impairment of the operation efficiency.
 In FIG. 11 there is illustrated an embodiment which uses the FET amplifier
 of FIG. 9 as each of the pre- and main amplifiers 12 and 13 and controls
 their gate bias voltages V.sub.g to enhance the amplifier efficiency.
 Between the input terminal 10 and the output terminal 14 there are
 connected in cascade the gain-controlled amplifier 11, the pre-amplifier
 12 and the main amplifier 13, and gate bias voltages are controlled which
 are applied to terminals 12G and 13G of the pre- and main amplifiers 12
 and 13. The battery 27 outputs the maximum bias voltage E.sub.H and the
 minimum bias voltage E.sub.L, which are fed not only to a voltage
 converter 53 but also to a switch 51, and the bias voltage E.sub.L is
 applied to a switch 52.
 The switch 51 responds to a control signal from the control signal
 generator 25 to select any one of the maximum bias voltage E.sub.H, the
 minimum bias voltage E.sub.L and its OFF state; this switch is connected
 to the terminal 12G. The voltage converter 53 responds to a control signal
 from the control signal generator 25 to output a given
 address-corresponding voltage within the range of from the minimum bias
 voltage E.sub.L to the maximum bias voltage E.sub.H, and the output
 voltage is applied to the gate bias terminals 12G and 13G via switches 54
 and 55, respectively.
 Within the range of values corresponding to the minimum to maximum values
 of the transmitting power controlling degree, for instance, from 0 to 255,
 the up-down counter 24 counts up by 1 upon each reception of the output
 increase control signal from the base station and counts down by 1 upon
 each reception of the output decrease control signal. The count value is
 provides, as an address corresponding to the transmitting power
 controlling degree, to the control signal generator 25 formed by a memory
 as referred to previously, from which a gain controlling degree for the
 gain-controlled amplifier 11, connection control signals for the switches
 51, 52, 54 and 55 and a bias controlling degree for the voltage converter
 53 are read out and applied to the respective parts.
 FIG. 8A shows, like FIG. 3A, the relationship between the transmitting
 power controlling degree (corresponding to the address) and the
 transmitting power of the radio transmission amplifier unit of FIG. 7;
 this example also divides the transmitting power controlling degree into
 three regions (I), (II) and (III), and effects control to increase the
 efficiency of the amplifier unit in each region.
 FIG. 8B depicts an example of gate bias control for the pre- and main
 amplifiers 12 and 13. In the small transmitting power region (I) the
 switches 51 and 52 are connected to the voltage E.sub.L and the switches
 54 and 55 are turned OFF so that the minimum gate bias voltage E.sub.L is
 applied to the two amplifiers 12 and 13. Accordingly, in this region the
 amplifiers 12 and 13 are set, for instance, on the load curve B as
 described previously with respect to FIG. 6B, and consequently, the drain
 current at their operating point takes a small value I.sub.b, making it
 possible to enhance the operation efficiency of the amplifiers 12 and 13
 as a whole in this region as depicted in FIG. 8C.
 In the medium transmitting power region (II) the amplifier 13 is supplied
 with the same low gate bias voltage E.sub.L as in the region (I) in this
 example. Hence, the switches 52 and 55 are in the same state as in the
 case of the region (I). The amplifier 12 is supplied with a gate bias
 voltage that goes higher with an increase in the transmitting power
 controlling degree as shown in FIG. 8B. That is, in the region (II) the
 output voltage of the voltage converter 53 is applied to the terminal 12G
 by turning OFF the switch 51 and ON the switch 54. The voltage converter
 53 varies the output voltage from E.sub.L to E.sub.H with the transmitting
 power controlling degree in the region (II). Accordingly, in this region,
 as the gate bias varies from E.sub.L to E.sub.H, the load line described
 previously with reference to FIG. 6B gradually shifts from the position B
 to A.
 In the large transmitting power region (III), as shown in FIG. 8B, the gate
 bias voltage V.sub.g for the amplifier 12 is held at the maximum value
 E.sub.H, and the gate bias voltage for the amplifier 13 is gradually
 increased from E.sub.L to E.sub.H with the transmitting power controlling
 degree. That is, in this region (III) the bias voltage E.sub.H is applied
 to the gate bias terminal 12G of the amplifier 12 by connecting the switch
 51 to the high bias voltage E.sub.H and turning OFF the switch 54. On the
 other hand, the output voltage of the voltage converter 53 is applied to
 the gate bias terminal 13G of the amplifier 13 by turning OFF the switch
 52 and ON the switch 55. In this region, too, the voltage converter 53
 outputs a voltage that varies from E.sub.L to E.sub.H with the
 transmitting power controlling degree.
 In the control signal generator 25 formed by a memory there are prestored,
 at each address corresponding to one particular value of the transmitting
 power controlling degree, control signals that are used to specify the
 gain to be set in the gain-controlled amplifier 11, the connections of the
 switches 51, 52, 54 and 55, and the voltage to be converted by the voltage
 converter 53; the output from the up-down counter is used as an address to
 read out these control signals.
 As described above, according to the FIG. 7 embodiment, by controlling the
 bias voltages for the inputs of the pre- and main amplifiers 12 and 13,
 the operation efficiency of the radio transmission amplifier unit is
 greatly improved in the region (I) wherein the transmitting power
 controlling degree is small, and in the medium and large regions (II) and
 (III), too, the efficiency is improved by the bias voltage control.
 Incidentally, while the above embodiment has been described in connection
 with the case where the transmitter of the mobile station generates the
 transmitting power controlling degree in response to the transmitting
 power control signal from the base station in the mobile radio system, the
 amplifier unit of the present invention is not limited specifically
 thereto; for example, it is possible to set a desired transmitting power
 in the transmitter by the user of the transmitting device without using
 the up-down counter 24 and to apply the set transmitting power as the
 transmitting power controlling degree to the control signal generator 25.
 This also applies to the embodiments described below.
 FIG. 9 illustrates an embodiment which combines the amplifier power-supply
 ON/OFF control in the FIG. 2A embodiment and the amplifier gate-bias
 control in the FIG. 7 embodiment. In FIG. 9 the parts corresponding to
 those in FIG. 2B and 7 are marked with the same reference numerals. In the
 embodiment, in the small transmitting power controlling region (I) the
 power supplies to the pre- and main amplifiers 12 and 13 are turned OFF so
 that the output from the gain-controlled amplifier 11 is provided to the
 terminal 14 (via the route A-B-E-F-G-D), and in the medium transmitting
 power controlling region (II) the power supply to the main amplifier 13 is
 turned OFF so that the output from the pre-amplifier 12 is provided to the
 output terminal 14 (via the route A-B-C-F-G-D). For the sake of brevity,
 however, the switches 15, 16, 18, 19, 21 and 22 for route switching use,
 depicted in FIGS. 2A and 4, are not shown but only the route points A, B,
 C, D, E, F and G are shown.
 As is the case with FIG. 7, the power-supply battery 27 provides a
 power-supply voltage E.sub.S to the power-supply terminals 12D and 13D of
 the amplifiers 12 and 13 via switches 28 and 29 and, at the same time,
 provides the high bias voltage E.sub.H and the low bias voltage E.sub.L to
 the voltage converter 53. Furthermore, the battery is capable of providing
 the high bias voltage E.sub.H to the gate bias terminals 12G and 13G via
 the switches 51 and 52. The voltage converter 53 is capable of outputting
 a desired voltage in the range of from the voltage E.sub.L to E.sub.H in
 response to a control signal and providing the output voltage to the gate
 bias terminals 12G and 13G via the switches 54 and 55.
 In the small transmitting power controlling region (I), since only the
 gain-controlled amplifier 11 is used as described previously with
 reference to FIG. 4, the switches 51, 52, 54 and 55 are all turned OFF and
 the switches 28 and 29 leading to the power-supply terminals 12D and 13D
 of the pre- and main amplifiers 12 and 13 so that the output from the
 gain-controlled amplifier 11 provided to the terminal 14 via the route
 B-E-F-G-F.
 In the medium transmitting power controlling region (II), the switches 52
 and 55 are both turned OFF so as to bypass the main amplifier 13 as
 referred to previously. Moreover, the switch 51 is turned OFF and the
 switch 54 ON to supply the output from the voltage converter 53 to the
 gate bias terminal 12G of the pre-amplifier 12, and as depicted in FIG.
 10A, the output from the voltage converter 53 is varied from E.sub.L to
 E.sub.H with an increase in the transmitting power controlling degree in
 this region.
 In the large transmitting power controlling region (III), the switch 52 is
 turned OFF and the switch 55 ON to apply the output voltage from the
 voltage converter 53 to the gate bias terminal 13G of the main amplifier
 13, and as depicted in FIG. 10A, the output voltage from the voltage
 converter 53 is varied from E.sub.L to E.sub.H as the transmitting power
 controlling degree is increased in this large transmitting power
 controlling region. Furthermore, the switch 51 is turned ON and the switch
 54 OFF to apply the maximum bias voltage E.sub.H to the gate bias terminal
 12G of the pre-amplifier 13.
 By such control as described above, the amplification efficiency with
 respect to the transmitting power controlling degree improves in any of
 the small, medium and large transmitting power regions (I), (II) and (III)
 as compared with the efficiency obtainable with the prior art. The
 transmitting power controlling degree, which is the output from the
 up-down counter 24, is provided as an address to the control signal
 generator 25 formed by a memory, from which the corresponding control
 signal is read out to set the gain of the gain-controlled amplifier 11,
 the voltage to be converted by the voltage converter 53 and the connection
 of the switches 28, 29, 51, 52, 54 and 55 and the switches 15, 16, 18, 21
 and 22 referred to in respect of FIG. 4.
 The efficiency of the pre- and main amplifiers 12 and 13, each formed by
 the FET as described previously, can be raised by operating them as Class
 C amplifiers. The embodiments described above perform Class AB
 amplification, but distortion occurs more or less. This distortion is
 affected, in particular, by the temperature and power-supply voltage of
 the main amplifier 13. Referring to FIG. 11, an example will be described
 below which compensates for this distortion. In FIG. 11 signals on two
 paths from a D/A converter 61 undergoes quadrature modulation by an
 quadrature modulator 62, and the modulated output is amplified by an
 amplifier 17, thereafter being provided to the output terminal 14. The
 temperature of the amplifier 17 is detected by a temperature sensor 63 and
 the detected temperature signal is converted by an A/D converter 69 to
 digital form. This digital value, the operating power-supply voltage of
 the amplifier 17 and a modulation signal S.sub.i from a modulation signal
 generator 64 are fed into an address generator 65, and an address
 generated by the address generator 65 is used to read out of a distortion
 compensating signal generator 66 formed by a memory a distortion
 compensating signal .phi..sub.i. The distortion compensating signal
 .phi..sub.i and the modulation signal S.sub.i are linearly combined in a
 distortion compensating circuit 67, and the combined output S.sub.i
 +.phi..sub.i is applied to the D/A converter 61.
 As depicted in FIG. 12, the modulation signal S.sub.i undergoes a phase
 distortion (-.phi..sub.i) in the amplifier 17, but a signal .phi..sub.i
 which cancels the distortion -.phi..sub.i is added to the signal S.sub.i
 and the added signal is fed to the quadrature modulator 62; hence, the
 modulation signal provided as the output from the amplifier 17 becomes a
 distortionless signal S.sub.i.
 FIG. 13 illustrates an example of a combination of the embodiments
 described above. In FIG. 13 the parts corresponding to those in FIG. 2A,
 4, 7A and 10 are identified by the same reference numerals and no
 description will be repeated with respect to them. A carrier signal of an
 oscillator 72 composed of a PLL and a VCO, based on a signal of a
 reference signal generator 71 is fed to the quadrature modulator 62, and
 the output from the quadrature modulator 62 is provided to the
 gain-controlled amplifier 11 after being up-converted in a frequency
 converter 74 by a high-frequency carrier signal from an oscillator 73
 composed of a PLL and VCO, based on the signal of the reference signal
 generator 71. The output from the gain-controlled amplifier is fed to the
 pre-amplifier 12 via an intermediate-frequency filter 75. The control
 signal generator 25 is adapted to generate also a signal 76 which controls
 the voltage to be converted by the voltage converter 53 and a bias
 switching control signal group 77 which controls the switches 51, 52, 54
 and 55 to switch between the input-side bias terminals 12G and 13G of the
 amplifiers 12 and 13 and the battery 27 and the voltage converter 53.
 Moreover, the voltage of the battery 27 is provided as the power-supply
 voltage to the address generator 65 after being converted by an A/D
 converter 78 to a digital value, and the switching control signal group 26
 is also applied to the address generator.
 EFFECT OF THE INVENTION
 As described above, according to the present invention, the operation
 efficiency of the radio transmission amplifier unit can be enhanced by
 bypassing the pre-amplifier 12 and/or the main amplifier 13 according to
 the transmitting power level and turning OFF the power supply to the
 bypassed amplifier. Besides, by effecting gain control for the
 gain-controlled amplifier 11 in accordance with the transmitting power
 level, the amplifier efficiency can be made relatively high at both medium
 and small levels, and the power consumption can be reduced. Alternatively,
 the efficiency can be raised by shifting the amplifier load curve by
 controlling the input-side bias voltages to the pre- and main amplifiers
 12 and 13 in accordance with the transmitting power.
 Moreover, the use of a distortion compensating means increases the
 efficiency although distortion occurs a little in the amplifier, that is,
 it is possible to achieve highly efficient amplification with the
 distortion compensated for.