Abstract:
An automatic and adjustable power control method and apparatus for optimally controlling the output power of a CDMA handset is provided. The method and apparatus utilize a single control signal to automatically control the gain of two frequency diverse variable gain stages of a transmitting portion of the handset by a multi-point hand-off technique. The multi-point hand-off technique partially varies the gain of a first stage to satisfy key system constraints and hands-off control to a second stage. The gain of the second stage is varied to satisfy additional system constraints. A second hand-off is performed so that the gain of the first stage may be varied again to maintain the optimal power control.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of wireless communications and, more particularly to a single-source frequency diverse power control method and apparatus for CDMA wireless cellular handsets. 
     2. Description of the Related Art 
     Code Division Multiple Access (CDMA) transmission schemes have become increasingly popular due to the recent growth of the cellular industry. CDMA is a spread spectrum technique whereby data signals are modulated by a pseudo-random signal, known as a spreading code, before transmission. The modulation of the data signals spreads the spectrum of the signals and makes them appear like noise to an ordinary receiver. When the same pseudo-random signal is used to demodulate (despread) the transmitted data signal at the CDMA receiver, the data signal can be easily recovered. 
     Currently, there exists an industry standard requiring CDMA handset transmitters to achieve a minimum of 73 dB of output power control. As is known in the art, the terms “gain control” and “power control” may be used synonymously since gain can be translated into power at any point during the transmit chain. The maximum required gain minus the minimum required gain is often referred to as gain range. In practice, the circuit components employed to achieve this output power control must also achieve additional power control to compensate for device, frequency, mode and temperature variations. These variations increase the minimum output power control of the components used in the CDMA transmitter to slightly over 100 dB of gain range. 
     FIG. 1 illustrates a typical transmit chain  100  used in a CDMA handset transmitter. The transmit chain  100  includes a digital-to-analog converter (DAC)  102 , modulator  104 , an intermediate frequency (IF) stage  116  and a radio frequency (RF) stage  118 . The IF stage  116  includes an IF amplifier  106  and an IF filter  108 . The RF stage  118  includes a RF upconverter  110 , oscillator  112  and RF amplifier  114 . 
     The DAC  102  receives digital baseband data from a remaining portion of the CDMA handset. Typically, the baseband data is received from a microcontroller or processor, such as a digital signal processor, responsible for controlling the operation of the handset. The baseband data is comprised of two signals known in the art as the in-phase I and quadrature Q signals. The DAC  102  converts the digital baseband data into analog I and Q signals and outputs the analog I and Q signals to the modulator  104 . 
     The modulator  104  inputs the analog I and Q signals, combines and modulates the signals into one IF signal which output to the IF amplifier  106 . The IF amplifier  106  has a gain controlled by a control signal. The IF amplifier  106  amplifies the IF signal and outputs it to the IF filter  108 . The IF filter  108  filters out any noise from the amplified IF signal and outputs the filtered IF signal to the RF upconverter  110 . As known in the art, the upconverter  110  converts the amplified IF signal into a RF signal. This conversion is controlled in part by the oscillator  112  connected to the upconverter  110 . The RF signal is output by the upconverter  110  to the RF amplifier  114 . The RF amplifier  114  has a gain controlled by a control signal. The RF amplifier  114  amplifies the RF signal such that the transmission power of the RF signal has the desired output power. This signal would then be supplied to an antenna where it is radiated to a CDMA base station. 
     Allocation of both gain and gain range through the transmit chain  100  results from tradeoffs based on the noise performance, linearity, current consumption and isolation issues of the chain  100 . Noise performance and linearity are known to have the biggest impact on system performance. 
     A CDMA system or handset is a full duplex system, that is, both the transmitter and receiver are operating simultaneously. In a CDMA handset, the transmit chain  100  must be designed to eliminate noise appearing at the receiver frequency band. This noise would interfere with a RF received signal. Therefore, the design of the transmitter must be such that its thermal noise is much lower than the thermal noise generated in the receiver. It is this constraint which drives the noise figure requirements, the IF gain allocation and is a critical factor in determining the electrical characteristics of the IF filter  108 . The high gain range is the constraint which forces the output power control to be performed across the two stages  116  (i.e., a two-stage power or gain control) ,  118  as opposed to being performed in either the RF or IF stage (i.e., a one stage power or gain control). 
     Today, almost all power control is performed via a two-stage power control having a variable gain. Typically, these methods utilize separate signals to control the gain of the two stages. It is desirable, however, to control the two frequency-diverse variable-gain stages (i.e., the IF and RF stages) with a single control signal. The use of one control signal would greatly enhance the overall handset design and circuitry by simplifying the interface between the transmit chain and the handset micro-controller. This would improve the cost associated with manufacturing the handset as well as its performance. 
     FIG. 2 is a block diagram illustrating an exemplary automatic and adjustable power control (APC) circuit  120  for controlling the two frequency-diverse variable-gain stages (i.e., the IF and RF stages  116 ,  118 ) of the transmit chain with a single APC control signal VapcMaster. The APC circuit  120  is implemented either in analog or digital circuitry. As shown in FIG. 2, the APC circuit  120  utilizes the VapcMaster signal to generate a first signal Vapc IF  to control the gain of the IF amplifier  106  and a second signal Vapc RF  to control the gain of the RF amplifier  114 . The VapcMaster signal is an analog voltage level whose amplitude is output by the handset micro-controller. As described below, this signal is used by the APC circuit  120  to generate the Vapc IF  and Vapc RF  control signals which are then respectively applied to the IF and RF amplifiers  106 ,  114 . In most wireless handset applications, the VapcMaster signal will be approximately 2.0 volts at maximum. 
     One method of controlling the gains of the IF and RF stages  116 ,  118  is by a sequential control method. This sequential control method varies the gain of one of the stages over the stages entire gain range prior to “handing off” the power control to the other stage. For example, the method would begin by varying the gain of the RF stage over the entire RF stage gain range. When this is complete, the method would continue by varying the gain of the IF stage over the entire IF stage gain range. During this method, the total gain G Tot , which is the addition of the gains of the IF and RF stages, must remain within the required gain range. The gain control of the sequential method is performed by the APC circuit as follows: 
     G Tot =G IF +G RF =Vapc IF *GS IF +Vapc RF *GS RF , where 
     Vapc IF =VapcMaster, Vapc RF =Vapc RF−min  when VapcMaster Min &lt;VapcMaster&lt;APC Handoff Level, 
     Vapc IF =Vapc IF−max , Vapc RF =VapcMaster when APC Handoff Level&lt;VapcMaster&lt;VapcMaster Max , 
     GS IF =the gain slope of the IF stage in dB/V=(total gain range of IF stage)/(control range of the IF stage in Volts) and 
     GS RF =the gain slope of the RF stage in dB/V=(total gain range of RF stage)/(control range of the RF stage in Volts). 
     It must be noted that the APC Handoff Level is a voltage level of the APC control signal VapcMaster at which the RF gain range has been completely exercised. Once the VapcMaster reaches the APC Handoff Level, the sequential method begins to exercise the gain of the IF stage over its entire gain range. 
     A second method of controlling the gains of the IF and RF stages  116 ,  118  is by a simultaneous control method. In the simultaneous control method the control lines for the RF and IF stages  118 ,  116  are both tied to the master control signal VapcMaster. Both stages  116 ,  118  would operate independently of each other since each stage&#39;s control voltage Vapc IF , Vapc RF  equals the master control signal VapcMaster. During this method, the total gain G Tot , which is the addition of the gains of the IF and RF stages, must remain within the required gain range. The gain control of the simultaneous method is performed by the APC as follows: 
     G Tot =G IF +G RF =Vapc IF *GS IF +Vapc RF *GS RF , where 
     Vapc IF =Vapc RF =VapcMaster, 
     GS IF =the gain slope of the IF stage in dB/V=(total gain range of IF stage)/(control range of the IF stage in Volts), 
     GS RF =the gain slope of the RF stage in dB/V=(total gain range of RF stage)/(control range of the RF stage in Volts) and 
     GS IF =GS RF  is not generally true. 
     It must be noted that the simultaneous method does not hand-off control as performed by the sequential method. Accordingly, there is no APC Handoff Level for VapcMaster in the simultaneous method. 
     A third possible gain control method would utilize a combination of the sequential and simultaneous methods. This would be difficult to implement, however, since simultaneous control requires Vapc IF =Vapc RF  while the sequential methods requires the two control voltages Vapc IF  and Vapc RF  to be independent of each other. 
     These methods, however, have some shortcomings which will become evident after a brief description of four major transmit chain design constraints. The first constraint (hereinafter referred to as “constraint #1”) mandates that as the gain is lowered, the current consumption must also be lowered. This allows for battery conservation and is easily implemented as part of the APC control scheme. For power conservation reasons, the stage which consumes more power ideally has its gain lowered first so that the circuitry reduces its current consumption as quickly as possible when the total gain is reduced from its maximum. This will be the RF stage in most transmit chains architectures. 
     The second constraint (hereinafter referred to as “constraint #2”) mandates that, for noise reasons, it is desirable to lower the gain of the RF stage since it makes a greater contribution to the output noise floor. 
     The third constraint (hereinafter referred to as “constraint #3”) mandates that, for linearity reasons, it is desirable to lower the gain of the IF stage first since its output feeds the RF stage in a cascaded manner. A lowering of the IF input to the RF stage without lowering the operating point of the RF stage allows the RF stage to operate in a more linear fashion, since the output power level is farther away from the non-linear range. 
     The fourth constraint (hereinafter referred to as “constraint #4”) mandates that, to compensate for variations in power levels along the transmit chain, it is desirable to extend both the IF and RF gain ranges. The extension of the IF gain range beyond what is required by the system specification indicates that under some conditions the IF output power will overdrive the RF stage causing non-linear operation and non-compliant adjacent channel emissions. 
     When compared with these designs constraints, it is evident that an RF-first sequential method would satisfy constraints #1 and #2 only while an IF-first sequential method would satisfy constraints #3 and #4 only. The simultaneous method would compromise all four of the constraints without properly satisfying any of them. The compromise method would be difficult to implement and would not optimize system performance with respect to the four design constraints. Accordingly, there is a desire and need for a power control scheme for a CDMA handset that utilizes a single control signal and provides optimal output power control. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing shortcomings, and for other reasons, the present invention is directed to a CDMA cellular handset with a simplified design for optimally controlling the output power of the handset. The invention comprises an automatic and adjustable power control method and apparatus that utilizes a single control signal to control two frequency diverse variable gain stages of a transmitting portion of the handset by a multi-point hand-off technique. 
     In one aspect of the present invention, an automatic and adjustable output power control method for a telephone handset is provided. The method includes the steps of providing a control signal; altering a gain of a first transmitting stage of the handset to satisfy at least one system parameter in response to a first variation of the control signal; altering a gain of a second transmitting stage of the handset to satisfy at least one additional system parameter in response to a second variation of the control signal; and varying the altered gain of the first transmitting stage in response to a third variation of the control signal. 
     In another aspect of the present invention, an apparatus for providing automatic and adjustable output power control to a transmitting portion of a telephone handset is provided. The apparatus includes a controller coupled to the transmitting portion of the handset. The controller receives a control signal from a second portion of the handset and: altering a gain of a first transmitting stage of the transmitting portion to satisfy at least one system parameter in response to a first variation of said control signal; altering a gain of a second transmitting stage of the transmitting portion to satisfy at least one additional system parameter in response to a second variation of said control signal; and varying said altered gain of the first transmitting stage in response to a third variation of said control signal. 
     In yet another aspect of the present invention, a telephone handset is provided. The handset includes a first controller providing a control signal; a transmitting circuit, said transmitting circuit including first and second transmitting stages, said transmitting circuit having an output power; and a power control circuit coupled to said transmitting circuit and said first controller. The power control circuit includes a second controller coupled to said first and second transmitting stages receiving said control signal from said first controller, said controller: altering a gain of said first transmitting stage to satisfy at least one system parameter in response to a first variation of said control signal; altering a gain of said second transmitting stage to satisfy at least one additional system parameter in response to a second variation of said control signal; and varying said altered gain of said first transmitting stage in response to a third variation of said control signal. 
     It is an object of the present invention is to provide an apparatus for controlling the output power of a wireless handset in an optimal manner. 
     It is another object of the present invention to provide an apparatus for controlling the output power of a wireless handset that simplifies the overall design of the handset. 
     It is yet another object of the present invention to provide an apparatus for controlling the output power of a wireless handset that reduces the overall cost of the handset. 
     It is a further object of the present invention is to provide a method for controlling the output power of a wireless handset in an optimal manner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other advantages and features of the invention will become more apparent from the detailed description of the preferred embodiments of the invention given below with reference to the accompanying drawings in which: 
     FIG. 1 illustrates an exemplary transmit chain utilized in a CDMA cellular handset; 
     FIG. 2 illustrates an exemplary automatic power control circuit used for controlling the two frequency-diverse variable-gain stages of a transmit chain with a single control signal; 
     FIG. 3 illustrates in flowchart form an exemplary multi-point hand-off process performed by the present invention; 
     FIG. 4 illustrates the output power control response according to the present invention; and 
     FIGS. 5-7 illustrate exemplary embodiments of an APC circuit for carrying out the multi-point hand-off processing performed by the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is directed to a CDMA cellular handset with a simplified design for optimally controlling the output power of the handset. The invention comprises an automatic and adjustable power control method and apparatus that utilizes a single control signal to control two frequency diverse variable gain stages of a transmitting portion of the handset by a multi-point handoff technique. 
     The present invention is preferably implemented in the APC circuit  120  by hardware (described in detail below with reference to FIGS.  5 - 7 ). The present invention utilizes a multi-point hand-off technique for controlling the output power of the transmit chain  100 . In this multi-point hand-off technique, the IF and RF stages  116 ,  118  are controlled alternatively. FIG. 3 illustrates an exemplary multi-point hand-off process  200  performed by the present invention. Initially, at step  202 , the process  200  would begin by lowering the gain of the IF stage, but only enough to satisfy constraints #3 and #4 described above. The point at which constraints #3 and #4 become satisfied is referred to as hand-off point #1. As will be shown below, the APC control signal VapcMaster will be at a hand-off #1 voltage level APCHandoffLevel 1 . It must be noted that the IF gain at hand-off point #1 will not be the minimum gain of the IF stage and therefore, the entire IF gain range is not being exercised at step  202 . The sequential, simultaneous and comprise methods would have exercised the entire range of the IF stage. Accordingly, the process  200  of the present invention is capable of satisfying constraints #3 and #4. 
     After reaching hand-off point #1, the process  200  would continue at step  204  by handing-off the power control to the RF stage. At step  206 , the gain of the RF stage is lowered from its maximum until constraints #1 and #2 are satisfied. The point at which constraints #1 and #2 become satisfied is referred to as hand-off point #2. As will be shown below, the APC control signal VapcMaster will be at a handoff #2 voltage level APCHandoffLevel 2 . Preferably, the gain of the RF stage is lowered to its minimum gain. During step  206 , the IF gain is not changed while the RF gain is being varied. 
     After reaching hand-off point #2, the process  200  would continue at step  208  by handing-off the power control to the IF stage. At this point, the IF gain is lowered from the hand-off point #1 gain to its minimum gain (step  210 ). The process continues at step  202  to maintain the optimal output power control achieved by the present invention. 
     The gain control of the multi-point hand-off process  200  is performed by the APC circuit as follows: 
     G Tot =G IF +G RF =Vapc IF *GS IF +Vapc RF *GS RF , where 
     Vapc IF =VapcMaster, Vapc RF =Vapc RF−min  when VapcMaster Min &lt;VapcMaster&lt;APC Handoff Level 1 , 
     Vapc IF =Vapc IF−mid , Vapc RF =VapcMaster when APC Handoff Level 1 &lt;VapcMaster&lt;APC Handoff Level 2 , 
     Vapc IF =VapcMaster, Vapc RF =Vapc RF−max  when APC Handoff Level 2 &lt;VapcMaster&lt;VapcMaster Max , 
     GS IF =the gain slope of the IF stage in dB/V=(total gain range of IF stage)/(control range of the IF stage in Volts) and 
     GS RF =the gain slope of the RF stage in dB/V=(total gain range of RF stage)/(control range of the RF stage in Volts). 
     These equations describe the instance where part of the IF gain range is exercised, then all of the RF gain is exercised and then the remaining portion of the IF gain range is exercised by the variation of the APC control signal VapcMaster. This can be seen pictorially in FIG. 4 which illustrates the transmitter output power attenuation (in dB) versus the level of the APC control signal VapcMaster (in volts). As is known in the art, attenuation corresponds to an amount of lessening of the gain. 
     The invention comprises an automatic and adjustable power control method and apparatus that utilizes a single control signal to control two frequency diverse variable gain stages of a transmitting portion of the handset by a multi-point hand-off technique. By effectively utilizing a single control signal, the present invention is capable of achieving an optimal output power control for the CDMA handset while reducing control circuitry and thus, lessening the design and cost of the handset. 
     The present invention is preferably implemented in the APC circuit by hardware. FIG. 5 illustrates one exemplary APC circuit  120   a  implemented using digital circuitry. The circuit  120   a  includes an analog-to-digital converter (ADC)  302 , two memory circuits  304 ,  306  and two digital-to-analog converters (DAC)  308 ,  310 . The ADC  302  is connected to the APC control signal VapcMaster and has multi-bit outputs connected to the memory circuits  304 ,  306 . The memory circuits  304 ,  306  can be read-only memory (ROM) or programmable read-only memory (PROM) containing digitally encoded voltage levels. The memory circuits  304 ,  306  are respectively connected to the two DACs  308 ,  310 . The output of the first DAC  308  is the Vapc IF  signal and the output of the second DAC  310  is the Vapc RF  as described above. When the analog APC control signal VapcMaster is received, the ADC  302  converts the signal into a digital signal which is applied to the memory circuits  304 ,  306  to look-up and obtain suitable digital voltage levels for Vapc IF  and Vapc RF . The two DACs  308 ,  310  convert the digital voltage signals into analog signals that are applied to the RF and IF stages of the transmit chain. 
     FIG. 6 illustrates a second exemplary APC circuit  120   b  implemented using digital circuitry. The circuit  120   b  includes an analog-to-digital converter (ADC)  302 , micro-controller  320  and two digital-to-analog converters (DAC)  308 ,  310 . The circuit  120   b  operates in a similar manner as the circuit  120   a  (FIG. 5) except that the micro-controller  320  calculates the new voltage levels as opposed to the look-up method used with the memory circuits  304 ,  306 . Since the micro-controller  320  can perform the calculations very fast, the single micro-controller  320  can be used to calculate and output the digital voltage levels for Vapc IF  and Vapc RF  in an alternating manner (thus, the digital voltages can be latched into the DACs  308 ,  310 ). 
     FIG. 7 illustrates an exemplary APC circuit  120 c implemented using analog circuitry. The circuit  120   c  includes four operational amplifiers (op-amps)  402 ,  404 ,  406 , 408  and a logic circuit  410  that are coupled together to generate suitable analog voltages for Vapc IF  and Vapc RF  without converting between analog and digital voltages. The APC control signal VapcMaster is applied to an input of all of the op-amps  402 ,  404 ,  406 ,  408 . The circuit  120   c  uses the logic circuit  410  to generate hold or latch signals HOLD which are applied to the first op-amp  402  to maintain or hold the Vapc IF  while the RF stage is being exercised and, likewise, to the fourth op-amp  408  to maintain or hold the Vapc RF  while the IF stage is being exercised. The logic circuit  410  generates the hold signals HOLD based on the outputs of the second and third op-amps  404 ,  406  which are comparing the APC control signal VapcMaster to their respective thresholds Vthreshold 1 , Vthreshold 2 . These thresholds Vthreshold 1 , Vthreshold 2  are set so that they correspond to the hand-off voltage levels (described above with reference to FIGS. 3 and 4) so that the logic circuit  410  may remove or apply the hold signal HOLD to the appropriate op-amp  402 ,  408 . An offset voltage OFFSET is used to offset the APC control signal VapcMaster so that the Vapc RF  and Vapc RF  can obtain different minimum (or maximum) voltage levels. The output of the first op-amp  402  is used as the Vapc IF  and the output of the fourth op-amp  408  is used as the Vapc RF . When the APC control signal VapcMaster is received, the circuit  120   c  generates the appropriate IF stage voltage Vapc IF  and RF stage Vapc RF  voltage as described above. 
     In addition, it must be noted that the present invention may be implemented in software or a combination of hardware and software. The invention may be implemented in any conventional CDMA cellular telephone and is not restricted to any particular CDMA cellular telephone circuit architecture. 
     While the invention has been described in detail in connection with the preferred embodiments known at the time, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.