Multi-level power amplifying circuitry for portable radio transceivers

MULTI-LEVEL POWER AMPLIFYING CIRCUITRY FOR PORTABLE RADIO TRANSCEIVERS

Background Art

The present invention is generally related to radio transceivers and more particularly related to an improved multi-level power amplifying circuitry for use in duplex battery-operated radio transceivers.

In the prior art, the maximum power output of power amplifiers in duplex battery-operated transceivers such as those used in portable radiotelephones was primarily dictated by the magnitude of the battery voltage and the need to conserve battery energy. Since vehicular operation was often desired in fringe areas, further away from the nearest fixed station than is typical in portable applications, there was a need for higher transmit power when such a portable radio transceiver is used in a vehicle. Furthermore, since the transmit and receive signals of such transceivers are duplexed, another power amplifier preceded by demultiplexing filters and followed by multiplexing filters and a separate power control circuit was required in order to boost the output power level by means of an external vehicle battery. This overall approach to boosting the output power level of such transceivers was costly and duplicative of transceiver filters, power amplifiers, and power control circuits.

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Objects and Summary of the Invention

Accordingly, it an object of the present invention to provide improved and inexpensive power amplifying circuitry that is responsive to different supply voltages for providing different sets of output power levels.

It is another object of the present invention to provide improved multi-level power amplifying circuitry that detects the presence of a vehicular adaptor and switches from a first set of power levels to a second set of power levels.

Briefly described, the present invention encompasses power amplifying circuitry for amplifying a radio frequency (RF) signal from a radio transmitter and maintaining the magnitude of said amplified RF signal at one of a plurality of levels. The unique power amplifying circuitry further comprises: a power amplifier; means for applying to said power amplifier one of first and second supply voltages from first and second voltage sources, said second supply voltage having a magnitude greater than the magnitude of the first supply voltage; and means coupled to said applying means for selecting a first set of said plurality of levels when the first supply voltage is applied to said power amplifier and a second set of said plurality of levels when the second supply voltage is applied to said power amplifier, said second set of levels including levels of greater magnitude than said first set of levels.

Brief Description of the Drawings

Figure 1 is a block diagram of a portable radio transceiver embodying the present invention together with vehicular adaptor circuitry.

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Figure 2 is a flow chart for the process used by the portable radio transceiver in Figure 1 for power level selection.

Figures 3, 4 and 5 are alternative embodiments of power amplifier stages for the power amplifier block in Figures 1, 6, 8, 10 and 12.

Figure 6 is another block diagram of a portable radio transceiver embodying the present invention together with vehicular adaptor circuitry.

Figure 7 is a flow chart for the process used by the portable radio transceiver in Figure 6 for power level selection.

Figure 8 is yet another block diagram of a portable radio transceiver embodying the present invention together with vehicular adaptor circuitry.

Figure 9 is a flow chart for the process used by the portable radio transceiver in Figure 8 to control the circuitry in the power control block thereof.

Figure 10 is yet another block diagram of a portable radio transceiver embodying the present invention together with vehicular adaptor circuitry.

Figure 11 is a flow chart for the process used by the portable radio transceiver in Figure 10 for power level selection.

Figure 12 is yet another block diagram of a portable radio transceiver embodying the present invention together with vehicular adaptor circuitry.

Figure 13 is a flow chart for the process used by the portable radio transceiver in Figure 12 for power level selection.

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Detailed Description of the Preferred Embodiment

In Figure 1, there is illustrated a portable radio transceiver 100 embodying the present invention together with a vehicular adaptor 180. Portable radio transceiver 100 includes a keyboard 114, display 116, microphone 110, speaker 112, battery 118, power control 150, voltage detector 140, power amplifier (PA) 122, circulator 124, transmitter filter 126, receiver filter 130, antenna 128 and transmitter, receiver and microcomputer 120. Vehicular adaptor 180 includes a vehicle battery 182, battery charger 184, voltage regulator 186 and antenna 188, all of which may be commercially available devices.

Referring to radio transceiver 100 in Figure 1, power control 150 includes a power detector 152, attenuator 154 coupled by three binary control signals to microcomputer 120, differential amplifier 156 and power control driver 158, all of which may be implemented as shown and described in U.S. Patent No. 4,523,155 (incorporated herein by reference thereto). Microcomputer 120 uses the three control signals applied to attenuator 154 to select one of eight different power levels of PA 122. The voltage Vref applied to differential amplifier 156 may be generated by a commercially available voltage regulator that is coupled to battery 118. PA 122 includes cascaded amplifier stages 132 and 134 and may also be arranged as illustrated in Figures 3, 4 and 5. PA 122 may be implemented with a commercially available device, such as, for example, a Motorola type MHW808 power amplifier. Likewise, circulator 124 and antenna 128 may be implemented with commercially available devices. Transmitter filter 126 and receiver filter 130 may be implemented as shown and described in U.S. Patent No. 4,431,977 (incorporated herein by reference thereto). Voltage detector 140 may be a conventional

CM00300G analog-to-digital converter (such as a Motorola type MC14442 converter) whose digitized output corresponds to the magnitude of Vsw, or may be a conventional comparator whose output changes from a low to a high state when VSW exceeds Vb by a predetermined amount. Transmitter, receiver and microcomputer 120 and associated blocks 110, 112, 114 and 116 may also be implemented by corresponding conventional circuitry shown and described in Motorola Instruction Manual no. 68P81046E60, entitled DYNATAC Cellular Portable Telephone״, or in U.S. Patent No. 4,486,624. This and other Motorola Instruction Manuals may be obtained from the Service Publications Department of Motorola, Inc., 1301 East Algonquin Road, Schaumburg, Illinois 60196, or from Motorola C & E Parts, 1313 East Algonquin Road, Schaumburg, Illinois 60196.

Referring to vehicular adaptor 180 in Figure 1, voltage regulator 186 is optional and may be bypassed as shown by dotted line 183. Voltage regulator 186 both protects and optimizes the efficiency of PA 122. For example, voltage regulator 186 protects PA 122 from damage due to over-voltage conditions arising during charging of vehicle battery 182 or jump starting of the vehicle. Voltage regulator 186 also optimizes the efficiency of PA 122 by maintaining Vr, and hence Vsw, at a voltage just large enough to enable PA 122 to reach the highest power level at which it is intended to operate. However, such highest power level may also be attained by bypassing voltage regulator 186 as shown by dotted line 183 without departing from the true spirit and scope of the present invention.

When portable radio transceiver 100 in Figure 1 is coupled by plug or otherwise to vehicular adaptor 180, plugs 185 and 187 insert into corresponding receptacles for coupling battery 118 to battery charger 184, Vsw to Vr from voltage regulator 186 (or directly from vehicle battery 182 as shown by dotted line 183) instead of

CM00300G battery 118, and antenna 188 to transmitter filter 126 and receiver filter 130 instead of antenna 128. As a result, power control driver 158 and PA 122 are now powered from vehicle battery 182 through voltage regulator 186 which provides a voltage Vr having a magnitude greater than the magnitude of the voltage Vb provided by battery 118. For example, regulator 186 may provide an 11V voltage, while battery 118 may provide a 6V voltage.

Microcomputer 120 in Figure 1 senses the presence of adaptor 180 by monitoring the VEH signal from voltage detector 140. If voltage detector 140 is implemented with a commercially available comparator (e.g., a Motorola type MC1710 comparator), the VEH signal changes state when Vsw exceeds Vb by a predetermined amount. The change in state of the VEH signal informs microcomputer 120 that adaptor 180 is present. Alternatively, if voltage detector 140 is implemented with a commercially available analog-to-digital converter (e.g., a Motorola type MC14442), the VEH signal is the digital representation of the magnitude of the Vsw voltage and, for example, changes from a representation of 6V to 11V. Microcomputer 120 compares the digital value of the VEH signal to the previous value or stored predetermined values to determine that adaptor 180 is present (see also description below for block 204 in Figure 8).

Microcomputer 120 in Figure 1 periodically monitors the VEH signal to determine when adaptor 180 is present. According to an important feature of the present invention, microcomputer 120 changes the operational class of transceiver 100 when adaptor 180 is present. The operational class is changed, for example, from class 3 to class 1 when adaptor 180 is present, and vice versa. In operational class 3, power control driver 158 and PA 122 are powered by battery 118 and produces a first set of power levels for PA 122. In the preferred embodiment, the first set of power levels includes six

- CMOO3OOG power levels. When switching to operational class 1, a second set of power levels for PA 122 is produced. In the preferred embodiment, the second set of power levels includes eight power levels, two more power levels higher in magnitude than those in the first set. Additional higher power levels may be produced in operational class 1 since the voltage Vr from regulator 186 has a magnitude greater than that of the voltage from battery 118. Furthermore, the exact value of power levels 1-6 may also change from Class 1 to Class 3 in order to compensate for changes in gain between antennas 188 and 128.

The foregoing operation of microcomputer 120 in Figure 1 is illustrated in more detail by the flow chart in Figure 2. The following description assumes that voltage detector 140 is a comparator. The flow chart is entered at START block 202 and proceeds to decision block 204 where a check is made of the VEH signal. IF the VEH signal has a first state (e.g., binary one) indicating that the adaptor 180 is present, YES branch is taken to block 206. In block 206, the operational class of transceiver 100 is changed from class 3 to class 1. Next, at block 208, a power level SPL is selected from the second set of eight levels, attenuator 154 is set to produce SPL, and microcomputer 120 returns to other tasks at block 214. In cellular radiotelephone systems, portable and mobile transceivers change power levels in response to commands transmitted from the radiotelephone central control terminal via base station radios (see U.S. Patent No. 4,485,486). Returning to decision block 204, if the VEH signal has a second state (e.g., binary zero) indicating that the adaptor 180 is not present, NO branch is taken to block 210. In block 210, the operational class of transceiver 100 is changed from class 1 to class 3. Next, at block 212, a power level SPL is selected from the first set of six levels, attenuator 154 is set to produce SPL, and microcomputer 120 returns to other tasks at block 214.

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The flow charts in Figures 2, 1, 9, 11 and 13 provide a detailed description of the process steps to be executed by microcomputer 120. The coding of the process steps in these flow charts into instructions of a suitable commercially available microcomputer is a mere mechanical step for a routineer skilled in the programming art.

According to another feature of the present invention, the various stages in PA 122 may be operated at a plurality of supply voltages for the purposes of setting its output power at a selected power level in the first or second sets of power levels and enabling PA 122 to reach higher power levels when transceiver 100 is coupled to vehicular adaptor 180. In the preferred embodiment, connecting different voltage sources to Vsw for supplying DC power to the final stage 134 of PA 122 allows the attainment of higher power levels in the second set than those in the first set of power levels. Also, in the preferred embodiment, power control driver 158 varies the supply voltage to stage 132 in order to maintain the output of PA 122 at the level selected by microcomputer 120. since power control driver 158 is also coupled to voltage Vsw, higher levels of DC voltage may also be applied to driver stage 132 for achieving the higher power levels in the second set of power levels.

Alternative implementations of PA 122 are shown in Figures 3, 4 and 5. These implementations are shown to indicate a variety of possible configurations achievable with commercially available power amplifying circuitry. In Figure 3, PA 122 is shown with two or more stages 302, 304 and 306, where DC voltage may be applied to the various stages by connection to Vsw or the power control signal. The connections of stages 302, 304 and 306 to Vsw and the power control signal may be configured to optimize PA performance characteristics, such as, efficiency, stability, continuity of power variation, and other requirements due to a particular application.

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In Figure 4, another alternative embodiment for PA 122 is shown where the power control signal is coupled to the DC biasing point of the first stage 402. The DC biasing point of one or more stages may be coupled to the power control signal in order to obtain improved stability and/or power output controllability. This arrangement is common practice when FET devices or forward-biased bipolar devices are used as the active device in a PA stage. Since it is not necessary to raise the DC supply voltage on all PA stages in order to obtain increased power output, stages 402 and 404 may be coupled to voltage Vb from battery 118.

In Figure 5, yet another alternative embodiment of PA 122 is shown where the power control signal is coupled to an electronically variable attenuator 502 which varies the RF input drive power to one or more amplifier stages 504, 506 and 508. Attenuator 502 may be one or more PIN diodes with variable bias or a resistor network with variable resistance. Combinations of the various features found in Figures 3, 4 and 5 may also be employed as needed to provide proper functioning of the circuit chosen for PA 122. The key feature common to all approaches, that makes the higher power levels possible, is the raising of supply voltages to selected PA stages and/or the power control driver when adaptor 180 is connected.

Turning to Figure 6, there is illustrated another portable radio transceiver 102 embodying the present invention together with another vehicular adaptor 190. Transceiver 102 is substantially the same as transceiver 100 in Figure 1 with the exception of power control 160, inverting gate 142 and data bus 144. Power control 160 includes a logarithmic amplifier 162, detector 164 and power control driver 166, all of which may be implemented as shown and described in U.S. patent application serial number 729,016, filed April 30, 1985, entitled ^,,Automatic

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Output Control Circuitry for RF Power Amplifiers with wide Dynamic Range, invented by Richard J. Vilmur and assigned to Motorola, Inc. (incorporated herein by reference thereto). Data bus 144 includes three control signals coupled to adaptor 190 for selecting one of eight power levels of PA 194. Inverting gate 142 is coupled to adaptor 190 for generating the VEH signal.

Adaptor 190 is similar to adaptor 180 in Figure 1 with the exception of power control 192, PA 194, regulator 191 and filter 196. Power control 192 may be implemented the same as power control 150 in Figure 1 or power control 160 in Figure 6. Voltage regulator 191 generates a reference voltage Vr for application to power control 192 and may be implemented with a commercially available device. PA 194 may be implemented in a similar manner to PA 122 in Figures 1, 3, 4 and 5. Filter 196 may be implemented the same as transmitter filter 126.

When transceiver 102 is coupled by plug or otherwise to adaptor 190, battery charger 184 is coupled to battery 118, the input of inverting gate 142 is grounded, data bus 144 is coupled to power control 192, transmitter filter 126 is coupled to PA 194 instead of antenna 128, and receiver filter 130 is coupled to antenna 188 instead of antenna 128. When plugged into adaptor 190, the output of PA 122 is set to a predetermined level, and PA 194 and power control 192 produce the desired power levels for application to filter 196 and antenna 188. Data bus 144 is used by microcomputer 120 to apply three power control signals to power control 192 for selecting the desired power level of PA 194. The power control signals of data bus 144 may be three binary signals for selecting one of eight levels as shown and described in U.S. Patent No. 4,523,155.

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Data bus 144 in Figure 6 may also include bidirectional serial data lines, such as, for example, those shown and described in U.S. Patent Nos. 4,369,516 and 4,486,624. Data lines in data bus 144 may be used to carry messages between microcomputer 120 and another microcomputer in power control 192, which may be arranged similar to microcomputer 120 in Figures 1, 6 and 8 for controlling power control 196. Such messages may convey power level and status information between the two microcomputers. For example, microcomputer 120 may periodically poll the microcomputer in power control 192 to determine when adaptor 190 is present and the current power level of PA 194.

Vehicular adaptor 190 in Figure 6 boosts the power level of PA 122 by means of PA 194 which is coupled to a higher voltage from vehicle battery 182. Microcomputer 120 monitors VEH or data bus 144 to determine when adaptor 190 is present. The VEH signal from inverting gate 142 has a binary one state when adaptor 190 is present and a binary zero state when adaptor 190 is not present. As described hereinabove, microcomputer 120 may also poll a microcomputer in power control 192 to determine when adaptor 190 is present. Upon determining that adaptor 190 is present, microcomputer 120 sets the power level of PA 122 to a predetermined level, such as, for example, a power level of the first set of power levels that will provide a signal of 11 dBm at the output of transmitter filter 126. Power control 192 is responsive to the power control signals from bus 144 for maintaining the output of PA 194 at the selected one of the second set of power levels, which, in the preferred embodiment, includes eight power levels.

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The foregoing operation of microcomputer 120 in Figure 6 is illustrated in more detail by the flow chart in Figure 7. The flow chart is entered at START block 702 and proceeds to decision block 706 where a check is made of the VEH signal. IF the VEH signal has a first state (e.g., binary one) indicating that the adaptor 190 is present, YES branch is taken to block 708. In block 708, the operational class of transceiver 102 is changed from class 3 to class 1. Next, at block 710, a power level K is selected from the first set of M levels using power control 160. The power level K may be selected to produce a desired power level at the output of transmitter filter 126 in Figure 6. Then at block 712, a power level SPL is selected from the second set of N levels using power control 192. Next, at block 714, power control 160 is set to produce level K and power control 192 is set to produce SPL, and microcomputer 120 returns to other tasks at block 722. As previously explained, the second set of N levels includes at least one power level that has a magnitude greater than that of the highest power level in the first set of M levels.

Returning to decision block 706 in Figure 7, if the VEH signal has a second state (e.g., binary zero) indicating that adaptor 190 is not present, NO branch is taken to block 716. In block 716, the operational class of transceiver 102 is changed from class 1 to class 3. Then, at block 718, a power level SPL is selected from the first set of M levels. Next, at block 720, power control 160 is set to produce SPL, and microcomputer 120 returns to other tasks at block 722. The number of power levels M in the first set and N in the second set may be selected to produce the desired number of power steps in a particular application.

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Referring next to to Figure 8, there is illustrated another portable radio transceiver 104 embodying the present invention together with vehicular adaptor 180. Transceiver 104 is substantially the same as transceiver 100 in Figure 1 with the exception of power control 170 and inverting gate 142. Power control 170 includes a power detector 172, a multiplexed analog-to-digital (A/D) converter 174, a digital-to-analog (D/A) converter 176 and power control driver 178. Power detector 172 and power control driver 178 may be implemented as shown and described in U.S. Patent No. 4,523,155. Converters 174 and 176 may be any suitable commercially available converters, such as, for example, Motorola type MC14442 and MC144111 converters, respectively. Inverting gate 142 is coupled to adaptor 180 for generating the VEH signal.

Microcomputer 120 in Figure 8 monitors VEH or utilizes converter 174 to determine when adaptor 180 is present. The VEH signal from inverting gate 142 has a binary one state when adaptor 180 is present and a binary zero state when adaptor 180 is not present. If VEH is monitored, microcomputer 120 periodically executes the flow chart in Figure 2.

According to another feature of the present invention, microcomputer 120 in Figure 8 may utilize converter 174 to convert Vsw to a digital representation which is compared to stored predetermined numbers to determine if adaptor 180 is present. Converter 174 periodically monitors either DPWR or Vsw in response to a select signal from microcomputer 120. In the case of Vsw, digital representations of Vb and Vr may be stored by microcomputer 120 to determine when adaptor 180 is present. The flow chart in Figure 2 may be used for this purpose by changing decision block 204 to read: Determine whether the digital representation of Vsw is greater than a digital representation of a voltage

CM00300G between that of Vb and Vr, such as, for example (Vb+Vr)/2״. Therefore, to monitor Vsw, microcomputer 120 periodically executes the flow chart in Figure 2, and in order to maintain the selected power level, SPL, microcomputer 120 periodically executes the flow chart in Figure 9.

The foregoing operation of microcomputer 120 in Figure 8 is illustrated in more detail by the flow chart in Figure 9. The flow chart is entered at START block 902 and proceeds to block 904 where DPWR is input from converter 174. DPWR is the digital representation of the output of detector 172. Next, at decision block 904, a check is made to see if the absolute value of DPWR-SPL is greater than TH, where SPL is a digital representation of the selected power level and TH is a predetermined number. TH represents a minimum difference that must exist between DPWR and SPL before a correction is made in OPWR. OPWR is the digital representation of the analog control signal that, when coupled to the power control driver 178, is used to make fine adjustments in the output of PA 122. If the absolute value of DPWR-SPL is less than TH, NO branch is taken to return to other tasks at block 908. Returning to decision block 906, if the absolute value of DPWR-SPL is greater than TH, YES branch is taken to decision block 910. In decision block 910, a check is made to see if DPWR is greater than SPL. If so, YES branch is taken to block 912 to reduce OPWR by DELTA. DELTA is a predetermined step size chosen to be small enough so that the resulting steps in DPWR are always less than TH. Otherwise, NO branch is taken from decision block 910 to block 914 where OPWR is increased by DELTA. Next, at block 916, OPWR is output to converter 176 and microcomputer 120 returns to block 904 to repeat the process steps of the flow chart until the absolute value of DPWR-SPL is less than TH, whereupon microcomputer 120 returns to other tasks at block 908.

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Referring next to Figure 10, there is illustrated another portable radio transceiver 106 embodying the present invention together with another vehicular adaptor 181. Transceiver 106 is substantially the same as transceiver 100 in Figure 1 with the exception of power control 151, inverting gate 142. Power control 151 contains an additional control path consisting of attenuator 155 and differential amplifier 157, which is, in turn, connected to a power control driver 189 in vehicular adaptor 181. Inverting gate 142 is coupled to adaptor 181 for generating the VEH signal. Adaptor 181 is similar to adaptor 180 with the exception of power control driver 189 which replaces voltage regulator 186. Power control driver 189 may be implemented in the same manner as power control driver 158 and may alternatively be located in power control 151, in which case vehicle battery 182 is coupled to plug 185.

When transceiver 106 in Figure 10 is coupled by plug or otherwise to adaptor 181, battery charger 184 is coupled to battery 118, filters 120 and 130 are connected to antenna 188 instead of antenna 128, the input of inverting gate 142 is grounded, the input of power control driver 189 is connected to the output of differential amplifier 157, and Vsw is coupled to Vc2 instead of Vb. Vehicular adaptor 181 boosts the maximum power level of PA 122 by supplying one or more stages in PA 122 with voltage Vc2 whose magnitude may exceed the magnitude of the voltage supplied by battery 118. This is made possible by the fact that power control driver 189 is coupled to vehicle battery 182, which has a voltage of greater magnitude than that of voltage Vb from battery 118.

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Microcomputer 120 in Figure 10 periodically monitors the VEH signal from inverting gate 142 to determine when adaptor 181 is present. Switching between operational class 3 and class 1 and selection of the appropriate power level SPL from the first or second set of power levels occurs in a similar manner to that shown and described herein with respect to Figure 2. When transceiver 106 is detached from adaptor 181, the selection of operational class 3 and a power level SPL from the first set of power levels is the same as that shown in Figure 2. However, when transceiver 106 is coupled to adaptor 181, maintaining a selected power level in the second set of power levels is dependent upon whether or not the magnitude of the selected power level exceeds the magnitude of the maximum power level in the first set of power levels. In this case, voltage Vc2 is coupled to stage 134 for attaining and maintaining such selected power level in the second set of power levels.

The foregoing operation of microcomputer 120 in Figure 10 is illustrated in more detail by the flow chart in Figure 11. The flow chart is entered at START block 802 and proceeds to decision block 804 where a check is made of the VEH signal. If the VEH signal has a first state (e.g., binary zero) indicating that adaptor 181 is not present, NO branch is taken to block 806. In block 806, the operational class of transceiver 106 is changed from class 1 to class 3. Next, at block 808, a power level SPL is selected from among the first set of M levels as commanded by the central control terminal. The power levels in the first set of M levels are preferably arranged in increasing order of magnitude such that level M has the highest magnitude. Next, at block 810 attenuator 154 is set to the value needed by power control 151 to maintain the selected power level SPL, and microcomputer 120 returns to other tasks at block 822.

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Returning to decision block 804 in Figure 11, if the VEH signal has a second state (e.g., binary one) indicating that adaptor 181 is present, YES branch is taken to block 812. In block 812, the operational class is changed from class 3 to class 1. Next, at block 814, a power level SPL is selected from among the second set of N power levels as commanded by the central control terminal. The number N of power levels in the second set is greater than the number M of power levels in the first set. Furthermore, the second set includes one or more power levels having a magnitude greater that that of level M, the highest power level in the first set. Next, at decision block 816, the magnitude of the selected power level SPL is compared to the magnitude of level M. If the magnitude of SPL is greater than the magnitude of level M, YES branch is taken to block 819. In block 819, attenuator 154 is set to its maximum attenuation, which is chosen to be great enough to keep the output from attenuator 154 below the magnitude of Vref for all possible output levels from PA 122. As a result, power control driver 158 produces a maximum output voltage (which typically is slightly below the magnitude of voltage Vb from battery 118). Next, at block 820, attenuator 155 is set to the value necessary to maintain the selected power SPL using power control driver 189, and microcomputer 120 returns to other tasks at block 822.

Returning to decision block 816 in Figure 11, if the magnitude of SPL is not greater than the magnitude of level M, NO branch is taken to block 817. In block 817, attenuator 155 is set to its maximum attenuation, which is chosen to be great enough to keep the output from attenuator 155 below the magnitude of Vref for all possible output levels from PA 122. As a result; power control driver 189 produces a maximum output voltage Vc2

CM00300G which typically has a magnitude that is slightly less than the magnitude of the voltage from vehicle battery 182. Next, at block 818, attenuator 154 is set to the value necessary to maintain the selected power level SPL using power control driver 158, and microcomputer 120 returns to other tasks at block 822.

Referring next to Figure 12, there is illustrated another portable radio transceiver 108 embodying the present invention together with vehicular adaptor 181. Transceiver 108 is substantially the same as transceiver 106 in Figure 10 with the exception of power control 171. Power control 171 contains multiplexed A/D converter 174 instead of attenuators 154 and 155, and D/A converters 176 and 177 instead of differential amplifiers 156 and 157.

The operation of microcomputer 120 in Figure 12 is illustrated in more detail by the flow charts in Figures 13 and 9. The flow chart in Figure 13 is substantially identical to the flow chart in Figure 11. The flow chart is entered at START block 602 and proceeds to decision block 604 where a check is made of the VEH signal. If the VEH signal has a first state (e.g., binary zero) indicating that adaptor 181 is not present, NO branch is taken to block 606. In block 606, the operational class of transceiver 108 is changed from class 1 to class 3. Next, at block 608, a power level selected from among the first set of M levels as commanded by the central control terminal. The magnitude of levels 1-M is arranged in increasing order with level M having the highest magnitude. Next, at block 610, converter 176 is selected, and microcomputer 120 exits at block 622 to block 902 in Figure 9, where the output of converter 176 is adjusted to the value needed to maintain the selected power level SPL.

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Returning to decision block 604 in Figure 13, if the VEH signal has a second state (e.g., binary one) indicating that adaptor 181 is present, YES branch is taken to block 612. In block 612, the operational class is changed from class 3 to class 1. Next, at block 614, a power level SPL is selected from among the second set of N power levels as commanded by the central control terminal. The second set of N levels includes at least one level with a magnitude greater than that of level M. Next, at decision block 616, the magnitude of the selected power level SPL is compared to the magnitude of level M. If the magnitude of SPL is greater than the magnitude of level M, YES branch is taken to block 619. In block 619, converter 176 is set to its maximum output. As a result, power control driver 158 produces a maximum output voltage (which typically is slightly below the magnitude of voltage Vb from battery 118). Next, at block 620, converter 177 is selected, and microcomputer 120 exits at block 622 to block 902 in Figure 9, where the output of converter 177 is adjusted to the value needed to maintain the selected power level SPL.

Returning to decision block 616 in Figure 13, if the magnitude of SPL is not greater than the magnitude of level M, NO branch is taken to block 617. In block 617, converter 177 is set to its maximum output. As a result, power control driver 189 produces a maximum output voltage Vc2 (which typically is slightly below the magnitude of the voltage from vehicle battery 182). An alternative implementation of block 617 is to set converter 177 such that power control driver 189 produces an output voltage substantially equal in magnitude to that produced by battery 118. Next, at block 618, converter 176 is selected, and microcomputer 120 exits at block 622 to block 902 in Figure 9, where the output of converter 176 is adjusted to the value needed to maintain the selected power level SPL.

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In summary, unique multi-level power amplifying circuitry has been described that may be advantageously utilized in portable radio transceivers which are insertable into a vehicular adaptor for operation from the vehicle battery. Upon detecting the presence of the vehicular adaptor, the power amplifier be operated at a second set of power levels which include levels greater than those in a first set of power levels for portable operation. The multi-level power amplifying circuitry of the present invention may be advantageously utilized in a variety of applications where battery-operated radio transceivers may be inserted into an adaptor for operation from another power source.