Abstract:
A power amplifier circuit arrangement including a driver amplifier, a switch, an amplifier path having a band pass filter and a power amplifier, and a bypass path which bypasses the power amplifier when excess gain and output power are not needed. When an RF-analog signal from the driver amplifier is switched to the amplifier path, the signal is band-pass filtered and amplified. Then the signal is split into an in-phase and a quadrature signal. Either the in-phase or the quadrature signal is inverted and summed with the other of the in-phase or quadrature signal, and the summed signal is transmitted to an output port. When the RF-signal from the driver amplified is switched to the bypass path, the power amplifier is turned off and the bypass path directs the signal to the output of the power amplifier, which appears as a high impedance to the signal. The signal reflects off the power amplifier to the output port. This design preserves the benefits of bypassing the power amplifier by reducing the amount of switching loss introduced into the circuit.

Description:
This application is a Continuation In Part Application of co-pending U.S. patent application Ser. No. 09/158,456 entitled “High Efficiency Switched Gain Power Amplifier”, filed on Sep. 22, 1998 and assigned to the Assignee of the present invention. 
    
    
     BACKGROUND INFORMATION 
     I. Field of the Invention 
     The present invention relates generally to power gain control for a power amplifier circuit and particularly to a power application circuit having greater power conservation in wireless communication device, such as a CDMA wireless phone. 
     2. Description of the Related Art 
     In many electronic environments, such as most hand-held communication systems including code-division-multiple-access (CDMA) or any form of time-division-multiple access (TDMA) technology, RF power output from a mobile unit varies in large dynamic ranges. In a CDMA radiotelephone system, multiple signals are transmitted simultaneously at the same frequency. The signals are spread with different digital codes, thus allowing detection of the desired signal while the unintended signals appear as noise or interference to the receiver. Spread spectrum systems can tolerate some interference, and the interference added by each new mobile station increases the overall interference in each cell site. Each mobile station introduces a unique level of interference, which depends on its received power level at the cell site. 
     The CDMA system uses power control to minimize mutual interference. A precise power control is critical to avoid excessive transmitter signal power that is responsible for contributing to the overall interference of the system. Power of the individual mobile stations varies with the distance between the mobile station and the base station and the number of other subscriber mobile stations in that base station or sector. 
     In a typical hand-held wireless unit, the power amplifier is biased class AB to reduce power consumption during periods of low transmit power, but power continues to be consumed. Typically an isolator is used to isolate the power amplifier from the effects of load impedance in subsequent stages. One method to avoid continuous battery draw is to employ a means to bypass the amplifier with switches, and then remove DC power from the amplifier. Such a power amplifier circuit has a power amplifier and an isolator. An RF-input is connected to a pole of a first switch. When the amplifier is on, the switch connects the RF-input to an input of the power amplifier. The RF-signal is amplified and output to the isolator, and then transmitted through the second switch to the RF-output of the power amplifier circuit. To bypass the power amplifier, the first switch connects the RF-input to the bypass path and the second switch transmits the signal to the RF-output. The switching employed introduces loss as the signal is processed. The drawback of this design is that the amplifier must overcome the added switching loss during times that higher transmit power is required. This can tend to cancel the benefits of bypassing. 
     SUMMARY OF THE INVENTION 
     What is needed in the art is a cellular phone or mobile station having power amplifier circuit which conserves power by turning off and bypassing the power amplifier when power demand is low and by using a driver amplifier (“DA”) as the power output amplifier. 
     An object of the present invention is to increase the efficiency of power amplifier usage by providing a circuit to bypass the power amplifier or power amplifiers when power demand is low. 
     Another object of the present invention is to reduce the effects of power loss after a signal is amplified by a power amplifier. 
     Another object of the present invention is to provide an improved power amplifier which requires less parts and is less complex to build. 
     Yet another object of the present invention is to provide an improved power amplifier which is less expensive to build. 
     These objects and others may be realized by the invention disclosed herein. In a mobile station having a power amplifier circuit, a switch operates to direct the received signal from a driver amplifier to either an amplifier path containing a band-pass filter and a power amplifier, or a bypass path. The bypass path bypasses the power amplifier when the power amplifier capability is not required. During the periods of low power operation, the amplifier is turned off. When the signal is passed through the bypass path it enters the isolated port of a hybrid circuit. The signal is transmitted to the output of the power amplifier. The power amplifier appears as a large impedance which is highly reflective because it is turned off. The reflected signal is then routed to the output port or front end of the circuit. With this configuration, an output switch becomes unnecessary and the power loss after the signal is amplified is reduced. 
     A first band-pass filter is placed in the amplification path such that filtering is also bypassed when the power amplifier is bypassed. When greater power amplification of the signal is needed, the signal flow is directed through a transmitter chain containing the first band-pass filter and a power amplifier (“PA”). The first filter in the transmitter chain cleans up noise added by the DA. The PA amplifies the signal which then is transmitted through an isolator and a second filter at the output of the circuit which cleans up noise added by the PA. A benefit of bypassing the PA is that it no longer adds noise to the signal. The second filter at the output of the circuit still filters the added effects of the PA, and when the signal routes through the bypass path, the second filter reduces noise added by the driver amplifier. Therefore, the first filter becomes unnecessary when the signal is passed through the bypass path. 
     This power amplification circuit provides reduced loss at the end of the amplifier, whereby greater power using less current at the output may be achieved. The configuration also reduces the loss in the bypass path when changing modes from amplification to bypass. The driver amplifier therefore becomes the output amplifier. 
     In another aspect of the present invention, bypassing the power amplifier enables the driver amplifier to be driven harder because it is the dominating source of distortion in the chain. The driver amplifier may be driven to a greater degree in the non-linear region than could be accomplished when using the power amplifier. By expanding the region over which the driver amplifier is driven, the cellular phone may be operated using the driver amplifier for a longer period of time, thus conserving battery power by keeping the power amplifier off for longer periods of time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters correspond throughout and wherein: 
     FIG. 1 is a block diagram of a mobile station of the present invention; 
     FIG. 2 is a plan drawing of the first embodiment of the present invention; 
     FIG. 3 provides a block diagrammatic representation of a mobile station spread spectrum transmitter in which may be incorporated an efficient power amplifier of the present invention; 
     FIG. 4 shows an exemplary implementation of an RF transmitter included within the spread spectrum transmitter of FIG. 2; 
     FIG. 5 is a plan drawing of the second embodiment of the present invention; 
     FIG. 6 is a plan drawing of the third embodiment of the present invention; 
     FIG. 7 is a plan drawing of the fourth embodiment of the present invention; and 
     FIG. 8 is a plan drawing of a sixth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a mobile station of the present invention and its signal processing. A mobile station  100  comprises circuitry for interfacing with system memory and the user  102 . The memory and user interface  102  is connected to a digital processor  104  which controls the signal processing. A receiving chain comprises a receiving IF/baseband signal processing circuit  106  connected to the digital processor  104 , and a receiving RF-signal processing circuit  108 . A transmitting chain comprising a transmitting IF/baseband processing circuit  120  is connected to the digital processor  104 . A transmitting RF processing circuit  122  includes the power amplifier circuit arrangement described in more detail herein. 
     A duplexer  124  controls the signal flow from the receiving chain and the transmitting chain and an antenna  126 . A codec circuit  110  is connected to the digital processor  104 . The circuit elements illustrated in FIG. 1, except the transmitting signal processing  122  disclosed herein, are generally known to those of ordinary skill in the art. Accordingly, the foregoing description and block diagram of FIG. 1, in addition to the disclosure of the power amplifier circuit arrangement of the present invention, sufficiently enable one of ordinary skill in the art to make and use the mobile station of the present invention. 
     FIG. 2 is a schematic diagram showing the power amplifier aspect of the invention. A power amplifier circuit, indicated generally by reference numeral  10 , comprises a power amplifier  32 , a circulator  52 , a series of switches,  20 ,  24  and  42 , and bypass paths  34  and  36  around the power amplifier  32 . An RF-input  12  having an RF-signal to be amplified is connected to a pole of first switch  20 . When amplification of the RF-signal is required, the power amplifier  32  is turned on and the switch  20  connects the RF-input  12 , via a path  28 , to an input of the power amplifier  32 . The power amplifier transmits the RF-signal toward the circulator  52 . The circulator  52  routes the signal to a port of the RF-output  54 . 
     When power demand is low and the power amplifier is turned off, the switch  20  switches the RF-signal to a bypass network  48  comprising a bypass path  36  and an attenuated path  34 . To send the signal through the bypass path  36 , switches  24  and  42  switch to a first position such that the signal flows through bypass path  36 . Switches  24  and  42  can also switch the signal to flow through the attenuated path  34 . From switch  42  the signal is transmitted to an input of circulator  52 . The circulator  52  routes the signal to the port connected to the output  50  of the power amplifier  32 . The output of the power amplifier  50  appears as a high impedance to the signal and thus the signal is reflected back to the circulator  52 , which routes the signal to the port of the RF-output  54  of amplifier circuit  10 . 
     FIG. 3 is a schematic diagram illustrating the use of the power amplifier of the present invention in the signal processing circuitry of a mobile station. In an exemplary CDMA system, orthogonal signaling is employed to provide a suitable ratio of signal-to-noise on the mobile-station to base-station link, or the “reverse” channel. Data bits  200  consisting of, for example, voice converted to data by a vocoder, are supplied to an encoder  202  where the bits are convolutionally encoded. When the data bit rate is less than the bit processing rate of the encoder  202 , code symbol repetition may be used such that the encoder  202  repeats the input data bits  200  in order to create a repetitive data stream at a bit rate which matches the operative rate of the encoder  202 . In an exemplary embodiment the encoder  202  receives data bits  200  at a nominal bit rate (R b ) of 11.6 kbits/second, and produced R b /r=34.8 symbols/second, where “r” denotes the code rate (e.g. ⅓) of the encoder  202 . The encoded data is then provided to a block interleaver  204 . 
     With the 64-ary orthogonal modulator  206 , the symbols are grouped into characters containing log 2 64=6 symbols at a rate of (1/r)(R b /log 2 64)=5,800 characters/second, with there being 64 possible characters. In a preferred embodiment each character is encoded into a Walsh sequence of length  64 . That is, each Walsh sequence includes 64 binary bits or “chips”, there being a set of 64 Walsh codes of length  64 . The 64 orthogonal codes correspond to Walsh codes from a 64 by 64 Hadamard matrix wherein a Walsh code is a single row or column of the matrix. 
     The Walsh sequence produced by the modulator  206  is provided to an exclusive-OR combiner  208 , where it is then “covered” or multiplied at a combiner with a PN code specific to a particular mobile station. Such a “long” PN code is generated at a rate R c  by a PN long code generator  210  in accordance with a user PN long code mask. In an exemplary embodiment the long code generator  210  operates at an exemplary chip rate, R c , of 1.2288 Mhz so as to produce four PN chips per Walsh chip. The output of the exclusive -OR combiner  208  is split into identical signals A and B. Signals A and B are input into the exclusive-OR combiners  256  and  254  of FIG. 4 as described below. 
     FIG. 4 is a schematic diagram showing an exemplary implementation of the RF transmitter  250  in a mobile station. In CDMA spread spectrum applications, a pair of short PN sequences, PN I  and PN Q , are respectively provided by a PN I  generator  252  and a PN Q  generator  254  to exclusive-OR combiners  256  and  258 , along with the output A and B from exclusive-OR combiner  208  of FIG.  2 . The PN I  and PN Q  sequences relate respectively to in-phase (I) and quadrature phase (Q) communication channels, and are generally of a length (32,768 chips) much shorter than the length of each user long PN code. The resulting I-channel code spread sequence  260  and Q-channel code spread sequence  262  are then passed through baseband filters  264  and  266 , respectively. 
     Digital to Analog (D/A) converters  270  and  272  are provided for converting the digital I-channel and Q-channel information, respectively, into analog form. The analog waveforms produced by D/A converters  270  and  272  are provided with a local oscillator (LO) carrier frequency signals Cos (2πft) and Sin (2πft), respectively, to mixers  288  and  290  where they are mixed and provided to summer  292 . The quadrature phase carrier signals Sin (2πft) and Cos (2πft) are provided from suitable frequency sources (not shown). These mixed IF signals are summed in summer  292  and provided to mixer  294 . 
     Mixer  294  mixes the summed signal with an RF frequency from frequency synthesizer  296  so as to provide frequency upconversion to the RF frequency band. The RF may then be bandpass filtered  298  and provided to an efficient parallel stage RF amplifier  10  of the invention. The filter  298  removes undesired spurs caused from upconversion  296 . Another filter (not shown) may be located following the amplifier circuitry to remove undesired spurs when the circuit is operating in bypass mode. In a bypass mode, the previous driver amplifier becomes the output amplifier and filtering may be necessary to prevent extra spurs from mixing in the non-linearities of the amplifier. This filtering may be accomplished by another filter (not shown), thus the band-pass filter  298  may be located in the amplification path as illustrated in FIGS. 5,  6  and  7  discussed below. This also increases flexibility in choosing gain steps. 
     FIG. 5 illustrates a second embodiment of the invention wherein the power loss after the power amplifier is minimized. A driver amplifier  280  produces an analog signal, which is switched by a first switch  20  between an amplifier path  28  and a bypass path  30 . In the amplifier path  28 , the signal is band-pass filtered  298  and amplified by a power amplifier  32 . The amplified signal is split by a first hybrid circuit  60  to produce an in-phase signal and a quadrature signal ninety degrees out of phase. Either of the in-phase signal or quadrature signal is inverted by a coupler or a second hybrid circuit  64  to produced an inverted signal according to means known by those of ordinary skill in the art. The inverted signal and the un-inverted signal, i.e. the other of the in-phase or quadrature signal, are summed by a summing feature of the second hybrid circuit  64  and transmitted toward the RF-output port  54  or antenna (not shown). Prior to being transmitted from an antenna, the signal is again filtered by a filter (not shown) to reduce any unwanted spurs or other effects. 
     When the first switch  20  routes the signal to the bypass path  30 , the signal is transmitted to an isolated port of the second hybrid circuit  64 . The second hybrid circuit  64  splits the signal into an in-phase signal and a quadrature signal ninety degrees out of phase. The first hybrid circuit  60  inverts either the in-phase signal or the quadrature signal and sums the two signals. The summed signal is transmitted to the output of the power amplifier  32 . The power amplifier  32  in this scenario is turned off to conserve power. 
     The turned-off power amplifier appears as a large impedance or a reflective load to the signal, which therefore reflects back to the first hybrid circuit  60 . The reflected signal is split by the first hybrid circuit  60  into an in-phase signal and a quadrature signal ninety degrees out of phase, input into the second hybrid circuit  64 , where one of either the in-phase or quadrature signal is inverted. The inverted signal is summed with the other un-inverted signal, filtered, and transmitted to the output port  54  or antenna. 
     When the bypass path is used, a second switch  43  positioned in the bypass path selectively connects the isolated port of the second hybrid circuit  64  with the first switch  20 . However, when the amplifier path  28  is utilized, the second switch  43  selectively connects the isolated port of the second hybrid circuit  64  to route reflected signals to a terminating resistor  45 . When the power amplifier  32  is bypassed, the signal reflected off of the power amplifier  32  acting as a reflecting load is filtered by a filter (not shown) prior to being radiated by the antenna (not shown). The circuit of the present invention does not need an output switch after the power amplifier, which simplifies the circuit and reduces the power loss after the power amplifier  32 . 
     FIG. 6 illustrates a third and preferred embodiment of the present invention which provides greater minimization of power loss after the amplifying the signal with power amplifiers. This embodiment provides a driver amplifier  280  producing an analog signal. The analog signal is switched by a first switch  20  between an amplifier path  28  and a bypass path  30 . In the amplifier path, the signal is band-pass filtered  298 , split by a first hybrid circuit  60  into an in-phase signal and a quadrature signal ninety degrees out of phase. The in-phase signal and the quadrature signal are each independently amplified by a first amplifier  31  and a second amplifier  32 , respectively. One of the amplified in-phase signal or the amplified quadrature signal is inverted by the second hybrid circuit  64  to produce an inverted signal. The inverted signal and the other un-inverted signal are summed in the second hybrid circuit  64 , filtered by a filter (not shown) and fed toward the RF-output port  54  or antenna (not shown). 
     The bypass path  30  provides a path from the first switch  20  to an isolated port of the second hybrid circuit  64 . The signal is split into an in-phase signal and a quadrature signal the hybrid circuit  64 . The in-phase signal is transmitted to the output of the first power amplifier  31  which is turned off and therefore appears as a reflective load to the signal. The quadrature signal is transmitted to the output of the second power amplifier  32 , which is turned off and therefore appears as a reflective load to the signal. Each reflected signal again enters the second hybrid circuit  64 , where either the in-phase signal or the quadrature signal one of the split signals is inverted and summed with the other signal. The summed signal is output to the output port  54 . Each circuit in FIGS. 5 and 6 also contains a filter (not shown) after the power amplifier or power amplifiers. Accordingly, a signal reflected from the high impedance output of the power amplifier is still band-pass filtered to reduce unwanted effects. 
     When the bypass path is used, a second switch  43  connects the isolated port of the hybrid circuit  64  with the first switch  20 . However, when the amplifier path  28  is utilized, the switch  43  connects the isolated port of the second hybrid circuit  64  with ground through a resistor  45 , which routes any reflected signal to ground. The circuit of this arrangement does not need an output switch and therefore simplifies the circuit and reduces the power consumption. 
     Shunt switches  47   a,    47   b  can be used to shunt the output of the power amplifiers  31 ,  32  when using the bypass path  30 . This will ensure that the output of each power amplifier  31 ,  32  is reflective without introducing significant loss. The shunt switches  47   a,    47   b  could be implemented with a pin diode, FET switch or other means. 
     FIG. 7 is a fourth embodiment of the present invention wherein the analog signal is switched by a first switch  20  between a bypass path  30  and an amplifier path  28 . However, band-pass filtering  298  only occurs in the amplifier path  28 . Accordingly, the signal is band-pass filtered  298  and fed to the power amplifier  32 , amplified, and transmitted to the circulator  55 , which routes the signal towards the RF-output port. When the first switch  20  directs the analog signal through the amplifier path, the circulator  55  is connected to ground through a second switch  43  and a resistor  45 . Accordingly, with this configuration, when reflected or returned RF-signals enter the circulator  55  from the direction of the RF-output port, the reflected signal is routed by the circulator  55  to ground. When the first switch  20  switches the analog signal to the bypass path  30 , the second switch  43  connects the bypass path  30  to the circulator  55 , and the signal is routed toward the output of the amplifier. This will appear as a high impedance, reflecting the signal back through isolator (shunt)  55  and to RF-output port  54 . 
     As in FIG. 6, a shunt switch  47   a  may be used to shunt the output of power amplifier  32  when using the bypass path  30 . This ensures that the output of PA  32  is reflective without introducing significant loss. The shunt  47   a  may be a PIN diode, FET switch or other means. 
     FIG. 8 illustrates another aspect of the power amplifier circuit of FIG. 2 without the attenuating path  34 . An analog signal is fed from a driver amplifier  280  through a band pass filter  298  to a first switch  20 . The switch  20  alternates between a bypass path  30  and an amplifier path  28 , wherein a power amplifier  32  amplifies the signal. A second switch  42  transmits the analog signal from either the bypass path  30  or the amplifier path  28  to a circulator  55 , which routes the signal to the RF-output port  54 . 
     The previous description of the preferred embodiment are provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.