Patent Application
20070018718
1. Field of the Invention
The present invention relates to a microwave transmitter and, more specifically, to a microwave and a method thereof applicable to various transmitter specifications for wireless communication systems, to attain the function of multi-mode transmission.
2. Description of Related Art
In wireless communication handset apparatuses, the major DC (direct-current) power loss results from RF (radio-frequency) power amplifiers. Therefore, one key point of the research on the design of an RF power amplifier always lies in that the RF power amplifier has high linearity without distorting the amplified signal, and has high efficiency to extend the communication time as well. In particular, the digital modulation technique of orthogonal frequency division multiplex (OFDM), which will be widely adopted in the future wireless communication systems, is characterized by significant time-varying envelopes, with a peak-average power ratio (PAPR) much higher than one for the existing wireless communication systems. In other words, the envelopes for OFDM may vary more drastically with time and may consequently require higher linearity for the RF power amplifier.
According to the prior art, the traditional type of design for an RF power amplifier may follow the trade-off between the linearity and the efficiency thereof, wherein a required increase in the linearity would necessarily lead to a decrease in the efficiency. Especially when the power of a traditional microwave transmitter is controlled to have an output of small power, the DC bias is still kept at a voltage for an output of large power, thereby resulting in excessive DC power dissipation so that the RF power amplifier has a decreased efficiency of its dynamic operation.
In the light of such a problem, ROC Patent No. 578369 discloses a high-efficiency power amplifier system, which may dynamically adjust the voltage supply for the RF power amplifier according to the magnitude of the output of power, to decrease the power dissipation resulting from the DC bias for an output of small power. However, for amplifying an RF modulated carrier with time-varying envelopes, it is further necessary that the voltage supply for the RF power amplifier is adjusted in following up the variation of the envelope magnitude of the output RF modulated carrier so as to greatly increase the efficiency of the dynamic operation.
Thus, the well-known envelope elimination restoration (EER) architecture of transmitter in the existing literature applies switched RF power amplifiers, e.g., class-D, class-E and class-F amplifiers, which have the characteristic that the amplitude of the output RF carrier is proportional to the voltage supply. As a result, the envelope signal of the input RF modulated carrier and the carrier that contains the information of the phase can be separated from each other and transmitted to the voltage supply terminal and the RF input terminal of the RF power amplifier, respectively, so that the envelope signal of the input RF modulated carrier can modulate the voltage supply terminal dynamically for the RF power amplifier to fulfill the purpose to have highly dynamic operation efficiency.
Referring to
In the block diagram as shown in
However, the EER transmitter according to the prior art applies the analogy technique to separate the envelope signal 103 from the phase-modulated carrier 104 and ultimately reconstructs the RF modulated carrier 107 at the output terminal, the obtained RF modulated carrier 107 has modulation accuracy not better than the traditional microwave transmitter that applies the IQ-modulation technique, where “I” is the in-phase component of the waveform, and “Q” represents the quadrature component. After the envelope signal 103 passes the low-pass filter 203 of the class-S modulator 105, the high-frequency components of the envelope signal 103 would be filtered off so that the amplified envelope signal would be distorted for the low-voltage region with high-frequency components, as shown in
For better modulation accuracy, U.S. Pat. No. 6,377,784 provides a polar modulation architecture, as shown in
Besides, in case of a modulation signal characterized by zero-crossing, such as QPSK or QAM, its phase would drastically change by 180° when the vector locus of the signal gets across the zero. Now the frequency generator 403 having the function of phase modulation typically cannot afford an adequate bandwidth for generating a phase-modulated carrier that has a drastically changing phase. Therefore, currently the polar modulation architecture is applicable successively to the multi-mode communication system that is not characterized by zero-crossing, such as the 2G-GSM and 2.5G-EDGE dual-mode transmitters, but is not applicable to the wireless communication system that employs a zero-crossing modulation signal, such as the 2G-GSM and 3G-CDMA dual-mode transmitters.
In the EER architecture of transmitter, when the supply voltage terminal of the switched RF power amplifier 106 is meeting a higher voltage of the envelope signal 103, the RF input terminal of the switched RF power amplifier 106 would requires a higher power of the input phase-modulated carrier 104 so as for the transistor to switch between a saturation region and a cutoff region while keeping the switched RF power amplifier 106 in a high-efficiency mode of operation. However, when the supply voltage terminal is meeting a lower voltage of the envelope signal 103, an equal power of the input phase-modulated carrier 104 would make both the gain and the efficiency of the switched RF power amplifier 106 decreased instead while causing the phase-modulated carrier 104 at the RF input terminal to leak to the output terminal, with an influence on the quality of the RF modulated carrier 107 at the output terminal. So, for the EER architecture of transmitter, U.S. Pat. No. 6,256,482 provides a method of dynamically adjusting the power of the phase-modulated carrier at the RF input terminal depending on the envelope magnitude that can effectively improve the efficiency of the dynamic operation for the EER transmitter but, it provides no solution to the problem described above that the EER architecture lacks modulation accuracy.
The RF power amplifier used in traditional microwave transmitters needs a trade-off between linearity and efficiency, whereas the EER architecture of transmitter has the advantage that both high linearity and high efficiency can be achieved. However, the main disadvantages of the EER architecture of transmitter include inadequate modulation accuracy, distortion that easily occurs the envelope signal is processed by the pulse-width modulator, decrease in the efficiency of dynamic operation due to fixing the power of the input carrier, and leakage of the carrier. However, no methods currently presented can overcome these disadvantages completely.
In view of this, the present invention provides a novel architecture of microwave transmitter, which largely introduces the baseband digital processing technique, as being capable of not only increasing the modulation precision for the signal but also adapting to various modulation specifications for wireless communication systems to attain the function of multi-mode transmission.
It is one object of the present invention to provide an architecture of microwave transmitter to improve the EER architecture of transmitter, by largely introducing the baseband digital processing technique to promote the tailor-made degree for IC (integrated circuit) design.
It is another object of the present invention to provide a architecture of microwave transmitter to improve the EER architecture of transmitter, by utilizing the baseband digital delta-sigma modulation technique to promote the accuracy and amplification efficiency for the envelope signal and by utilizing the pre-distortion technique to endow the pre-distorted IQ-modulated carrier with a time-varying characteristic so that the power of the input carrier can be adjusted flexibly and, thereby, the problems with respect to the efficiency of dynamic operation and the leakage of the carrier can be reformed.
To fulfill the purpose described above, the microwave transmitter of the present invention performs a two-terminal dynamic modulation with respect to the voltage supply terminal and the RF input terminal of a RF power amplifier, the modes of modulation including envelope modulation, phase modulation and IQ modulation, wherein the modulated signal at the voltage supply terminal may be an envelope signal, a pre-distorted envelope signal, or a modulated signal containing components of envelopes, while the modulated signal at the RF input terminal may be an IQ-modulated carrier, a pre-distorted IQ-modulated carrier, a phase-modulated carrier, a pre-distorted phase-modulated carrier, or a phase-modulated carrier containing components of envelopes.
The microwave transmitter of the present invention has the envelope signal generated directly by a baseband digital processor and processed by a digital delta-sigma modulator instead of the pulse-width modulator as required, wherein the digital delta-sigma modulator does not need a source of triangle waves and, thus, can be integrated into the baseband digital circuit.
Further, the microwave transmitter of the present invention replaces the phase-modulated carrier having constant envelope magnitude with the pre-distorted IQ-modulated carrier for input to the RF input terminal of the RF power amplifier, endowing the pre-distorted IQ-modulated carrier with a time-varying characteristic so that the power of the input carrier can be adjusted flexibly and, thereby, the problems with respect to decrease in the efficiency of dynamic operation and leakage of the carrier can be reformed, wherein the IQ-modulated carrier, as having been processed with the pre-distortion technique, is combined with the envelope signal for the RF power amplifier to reconstruct the power-amplified RF modulated carrier without distortion at the RF output terminal.
The microwave transmitter realized according to the present invention and the wireless communication handset apparatus performed in light of the teaching of the present invention can reform the disadvantage of the existing EER architecture of transmitter with baseband digital technique, in contrast to the trade-off between high linearity and high efficiency of traditional microwave transmitters. Except for keeping the characteristic that both high linearity and high efficiency can be achieved, the present invention further promotes the quality of the output RF modulated carrier and the efficiency of the dynamic operation and, also, adapts more easily to various modulation specifications for wireless communication systems to attain the function of multi-mode transmission.
Although the present invention will be full described by reference to the appended drawings for preferred embodiments of the present invention, it will be understood before the description that those skilled in the art may modify the invention described herein while acquire the function of the present invention. Therefore, it will be understood that the following description is a general disclosure to those skilled in the art and, thus, the structure of the present invention should be applicable to different architectures of microwave transmitter. The application of the present invention should not be only limited to the preferred embodiments in the following description.
First, referring to
E=√{square root over (I2Q2)}. (1)
In (1), E is given as the amplitude in the polar coordinate and, also, represents the envelope signal corresponding to the input IQ signals, wherein the operations of squaring and rooting are not easy to achieve with a digital circuit. For this, refer to the CORDIC algorithm disclosed by Ray Andraka in FPGA '98. Proceedings of the 1998 ACM/SIGDA Sixth International Symposium on Field Programmable Gate Arrays, pp. 191-200 (22-24, Feb. 1998), wherein the desired magnitude of the envelope is successively approximated by iteration. Then the digital envelope signal obtained passes the delta-sigma modulator 502 to convert to a two-stage signal. The architecture of the delta-sigma modulator 502 is shown by reference to
Y=X+(1−z−1)e, (2)
where e represents the quantified noise introduced by the quantifier. From (2), it is found that the output signal Y equals to the input signal X plus the quantified noise after difference while the difference is equivalent to an action of driving the energy of the signal toward high frequency in the frequency domain. The signal Y obtained at the output terminal is a two-stage pulse wave signal being applicable to the high-efficiency switched amplifier 503 for amplification, and, as it passes the low-pass filter 504 to have the quantified noise that have been driven towards high frequency filtered off, an amplified input envelope waveform is obtained. This amplified envelope signal is input to the voltage supply terminal of an RF power amplifier 508, so that the carrier output from the RF power amplifier 508 is amplitude-modulated by the time-varying envelope signal from the voltage supply terminal.
Along the path for the pre-distorted IQ modulated signal processing, the architecture of transmitter of the present invention comprises a first pre-distorter 505, a plurality of digital-to-analog converters 506 and an IQ-modulator 507. The present invention has the input IQ signals passing the digital first pre-distorter 505 and then has the pre-distorted IQ signals converted to the corresponding analog signal through the plurality of digital-to-analog converters 506, thereby producing the IQ-modulated carrier with the IQ-modulator 507 as a signal at the RF input terminal of an RF power amplifier 508. This endows the input carrier with a time-varying envelope characteristic so that the power of the input carrier can be adjusted flexibly and, thereby, the problems with respect to the efficiency of dynamic operation and the leakage of the carrier can be reformed. Nevertheless, the IQ-modulated carrier, as having been processed with the pre-distortion technique, is combined with the envelope signal for the RF power amplifier 508 to reconstruct the power-amplified RF modulated carrier without distortion at the output terminal. In different embodiments of the present invention, it is as well that the input IQ signals pass the first pre-distorter 505 at first and the output signals are then input to the envelope generator 501 and the plurality of digital-to-analog converters 506, respectively.
In the architecture of multi-mode microwave transmitter of the present invention, the first pre-distorter 505 uses the digital technique to compensate the nonlinear relation between the input and output signals of the transmitter. The major causes come from the nonlinear phenomena in the RF power amplifier 508, which may be the amplifier circuit such as one of class-A, class-B, class-AB, class-C, class-D, class-E or class-F. The circuitry functions of the first pre-distorter 505 include changing the IQ baseband signal, the envelope signal, the phase signal or the amplitude of the RF carrier, for compensating the nonlinear phenomena of the elements contained in the transmitter circuit and thereby seeking an improvement of the parameters, e.g., the modulation accuracy and the linearity, of the RF-modulated carrier at the output terminal.
The embodiments of the present invention have advantages in achieving hardware implementation, including that the adopted envelope generator 501, the delta-sigma modulator 502 and the first pre-distorter 505 are realized in a manner of the baseband digital processing, that the high-efficiency switched amplifier 503 and the low-pass filter 504 may be realized by using the baseband analog signal processing technique, and the plurality of digital-to-analog converters 506 is realized by using the baseband mixed signal processing technique, wherein those circuits may be altogether referred to as a multi-mode operation efficiency promoting baseband processor 509. Since the existing design of the baseband signal-processing chip would lead to functions that may be fairly powerful, which tend to meet various modulation specifications for wireless communication systems, the technique of the present invention may suitably apply to the multi-mode wireless systems. If the multi-mode operation efficiency promoting baseband processor 509 is disabled, then the remaining IQ-modulator 507 and RF power amplifier 508 may be combined to be a traditional architecture of IQ-modulated microwave transmitter 510 that has low efficiency but high linearity; if the multi-mode operation efficiency promoting baseband processor 509 is enabled, then it is improved to be a architecture of multi-mode microwave transmitter that achieves both high efficiency and high linearity. This means that the traditional architecture of IQ-modulated microwave transmitter may be deemed a special example of the present embodiment and can be extended to two architectures of transceiver chip of a wireless handset apparatus, as further described in the following.
Referring
Referring
According to the embodiments shown in
In addition, an important characteristic of the transmitter of the present invention may be found from
Referring
Along the path for the pre-distorted and delayed IQ modulated signal processing, the architecture of transmitter of the present invention comprises a first pre-distorter and delay control unit 112, a plurality of digital-to-analog converters 116 and a IQ-modulator 117. The present invention has the input IQ signals passing the first pre-distorter and delay control unit 112, and then has the pre-distorted and delay-corrected IQ signals converted to the corresponding analog signals through the plurality of digital-to-analog converters 116, thereby producing the IQ-modulated carrier with the IQ-modulator 117, as a signal at the RF input terminal of the RF power amplifier 118. This endows the input carrier with a time-varying envelope characteristic so that the power of the input carrier can be adjusted flexibly and, thereby, the problems with respect to the efficiency of dynamic operation and the leakage of the carrier can be reformed. Nevertheless, the IQ-modulated carrier, as having been processed with the pre-distortion technique, is combined with the envelope signal for the RF power amplifier 118 to reconstruct the power-amplified RF modulated carrier without distortion at the output terminal. Said delay control unit is used for coordinating the two paths for signal processing, so as to synchronize the signals along the twp paths. In different embodiments of the present invention, it is as well that the input IQ signals pass the first pre-distorter at first and the output signals are then input to the envelope generator and the plurality of digital-to-analog converters, respectively.
Because of the process-drift problem in the manufacturing process, the elements would show slight variations; in use of the circuits, the temperature would often change with the change in the environment and the operation time. With a variety of change in the external environment, the characteristic of the circuits would also change significantly and, therefore, the output of the RF power amplifier can be feedback to the pre-distorter under the requirement for robustness, as shown in
Referring to
Along the path for the delayed IQ modulated signal processing, the architecture of transmitter of the present invention comprises a delay control unit 122, a plurality of digital-to-analog converters 126, a IQ-modulator 127, a tunable gain amplifier 128 and a feedback control unit 140, wherein the feedback control unit 140 comprises an envelope detector 141, an analog-to-digital converter 142 and a second pre-distorter 143. The envelope detector 141 detects the output terminal of the RF power amplifier 128′ to produce the feedback envelope signal, the feedback envelope signal is digitized through the analog-to-digital converter 142, and the digitized feedback envelope signal together with the delayed digital envelope signal from the envelope generator is received by the second pre-distorter 143.
The present invention has the input IQ signals passing the delay control unit 122, and then has the delay-corrected IQ signals converted to the corresponding analog signals through the plurality of digital-to-analog converters 126, thereby producing the IQ-modulated carrier with the IQ-modulator 127, as a signal at the RF input terminal of the RF power amplifier 128′ after amplification by the tunable gain amplifier 128.
The gain of the above-described tunable gain amplifier 128 is determined by the output of the second pre-distorter 143, which receives the output signal from the analog-to-digital converter 142 (digitized feedback envelope signal) and the output delayed signal from the envelope generator 121 (digital envelope signal), to produce a control signal for controlling the gain of the tunable gain amplifier 128. In different embodiments of the present invention, it is as well that the input IQ signals pass the delay control unit at first and the output signals are then input to the envelope generator and the plurality of digital-to-analog converters, respectively.
Referring to
The present invention has the input IQ signals passing the envelope generator 131 to generate the corresponding envelope signal. The digital envelope signal obtained passes the delay control unit 132 and then passes the delta-sigma modulator 133 to convert to an at least two-stage signal. The signal at the output terminal of the delta-sigma modulator 113 is an at least two-stage pulse wave signal, being converted to a current supply for an RF power amplifier 138′ by using the at least one bit control current source 134, and, as it passes the low-pass filter 135 to have the quantified noise that have been driven towards high frequency filtered off, an amplified input envelope waveform is obtained. This envelope signal is the current supply for the RF power amplifier 138′, for which the current supply is controlled to fulfill the purpose to control the RF power amplifier 138′, so that the carrier output from the RF power amplifier 138′ is amplitude-modulated by the time-varying envelope signal from the current supply terminal.
Along the path for the delayed IQ modulated signal processing, the architecture of transmitter of the present invention comprises a delay control unit 132, a plurality of digital-to-analog converters 136, a IQ-modulator 137, a tunable gain amplifier 138 and a feedback control unit 150, wherein the feedback control unit 150 comprises an envelope detector 151, an analog-to-digital converter 152 and a second pre-distorter 153. The envelope detector 151 detects the output terminal of the RF power amplifier 138′ to produce the feedback envelope signal, the feedback envelope signal is digitized through the analog-to-digital converter 152, and the digitized feedback envelope signal together with the delayed digital envelope signal from the envelope generator is received by the second pre-distorter 153.
The present invention has the input IQ signals passing the delay control unit 132, and then has the delay-corrected IQ signals converted to the corresponding analog signals through the plurality of digital-to-analog converters 136, thereby producing the IQ-modulated carrier with the IQ-modulator 137, as a signal at the RF input terminal of the RF power amplifier 138′ after amplification by the tunable gain amplifier 138. The gain of the above-described tunable gain amplifier 138 is determined by the output of the second pre-distorter 153, which receives the output signal from the analog-to-digital converter 152 (digitized feedback envelope signal) and the output delayed signal from the envelope generator 131 (digital envelope signal), to produce a control signal for controlling the gain of the tunable gain amplifier 138. In different embodiments of the present invention, it is as well that the input IQ signals pass the second pre-distorter at first and the output signals are then input to the envelope generator and the plurality of digital-to-analog converters, respectively. In different embodiments of the present invention, it is as well that the input IQ signals pass the delay control unit at first and the output signals are then input to the envelope generator and the plurality of digital-to-analog converters, respectively. After a detailed description of the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that various changes and modifications can be performed without departing the scope and spirit of the appended claim, while the present invention is not limited to the implementation of the embodiments set forth in the specification.
| Number | Date | Country | Kind |
|---|---|---|---|
| 94120407 | Jun 2005 | TW | national |
| Number | Date | Country | |
|---|---|---|---|
| 60812097 | Jun 2006 | US |
