Patent Application
20120002755
1. Field of the Invention
This invention relates to using a multi-level pulse modulation technique to implement a polar transmitter, and more particularly, to a multi-level pulse modulated polar transmitter and a method of generating multi-level envelope signals carrying modulated RF signal that may enhance the efficiency and bandwidth of a power amplifier and reduce out-of-band emissions.
2. Description of Related Art
In general, a power amplifier has long been known as the most power-consuming component in a radio-frequency (RF) transmitter. By improving the power amplifier efficiency, the overall battery life can be greatly increased. The envelope elimination and restoration (EER) method, which was first proposed in “Single-sideband transmission by envelope elimination and restoration” (Proc. of the IRE, pp. 803-806, July 1952, L. R. Kahn), may efficiently amplify an RF signal. The EER method splits the RF signal into a constant-envelope modulated signal and an envelope signal, amplifies the constant-envelope modulated signal, and restores the signal based on the envelope signal such that high overall power efficiency may be attained.
The EER method is implemented in “An envelope elimination and restoration power amplifier using a CMOS dynamic power supply circuit” (IEEE MTT-S Int. Microwave Symp. Dig., vol. 3, pp. 1591-1522, June 2004, J.-H. Chen, K. U-Yen, and J. S. Kenney) and “L-band transmitter using Kahn EER technique” (IEEE Trans. Microwave Theory Tech., vol. 46, no. 12, pp. 2220-2225, December 1998, F. H. Raab, B. E. Sigmon, R. G. Myers, and R. M. Jackson), in which a highly efficient power supply circuit is used to dynamically modulate the drain or collector of a non-linear, but highly efficient RF power amplifier. One of the major problems in implementing a Kahn EER transmitter is to synchronize the phase and envelope paths. The non-synchronization of the phase and envelope paths may create unwanted out-of-band emissions. Conventional EER transmitters use an L-C low-pass filter to filter the output of the switching envelope amplifier or dynamic bias circuit. The low-pass filter, however, creates significant delay that requires the phase data to be delayed accordingly using shift registers or delay circuits. For these transmitters, the phase path may require as many as 16 bits per clock for storage. Using the shift registers to store such data may adversely increase the area and cost of the transmitter.
Pulse modulation of the input signals using sigma-delta modulation (Σ-Δ Modulation) for implementing a Kahn EER transmitter has been proposed in “An improved Kahn transmitter architecture based on Delta-Sigma Modulation” (IEEE MTT-S Int. Microwave Symp. Dig., vol. 3, pp. 1327-1330, June 2004, Y. Wang), “An EER transmitter architecture with burst-width envelope modulation based on triangle-wave comparison PWM” (Proc. IEEE Int. Symp. PIMRC, pp. 1-5, September 2007, M. Taromaru, N. Ando, T. Kodera, and K. Yano) and “A transmitter architecture for nonconstant-envelope modulated modulation” (IEEE Trans. Circuit and Syst. II, vol. 53, no. 1, pp. 13-17, January 2006, C. Berland, I. Hibon, J. F. Bercher, M. Villegas, D. Belot, D. Pache, and V. Le Goasccoz). The main benefit of using this technique is the omission of the low-pass filter in the envelope path. By omitting the low-pass filter, the delay in the envelope path is reduced significantly, and hence synchronizing the phase and envelope paths using shift registers may be simplified. However, the use of the pulse-modulated EER method requires high-quality band-pass filters to filter the unwanted out-of-band emissions created by pulse modulation or SDM noises, which hampers the wide use of the EER method. Pulse modulation of the input signals using pulse-width modulation (PWM) was shown in “A transmitter architecture for nonconstant-envelope modulated modulation” (IEEE Trans. Circuit and Syst. II, vol. 53, no. 1, pp. 13-17, January 2006, C. Berland, I. Hibon, J. F. Bercher, M. Villegas, D. Belot, D. Pache, and V. Le Goasccoz), but was concluded as unattractive since spurious emissions are too high.
The aforesaid conventional EER transmitters require the use of envelope detectors and radio frequency (RF) limiters to obtain constant-envelope modulated RF signals. Thanks to the advancement of modern digital signal processing technology, it is now possible to directly generate the phase and envelope signals digitally to implement a polar transmitter. The polar transmitter may be applied in cellular phones for CDMA2000 and W-CDMA standards. In the related applications, a high-quality bass-pass filter is required at the output end of the transmitter, to suppress the unwanted out-of-band emissions generated from the PWM. The modern cellular phones supporting CDMA2000 and W-CDMA standards have high-quality surface-acoustic-wave (SAW) filters between the antennas and the power amplifiers. However, unless the PWM sampling frequency is sufficiently high, the SAW filter alone is not adequate to suppress the unwanted out-of-band emissions.
Therefore, how to provide a polar transmitter that may resolve the drawbacks of the prior art, to suppress the out-of-band emissions generated from the PWM and enhance the signal bandwidth and efficiency of the power amplifier, is crucial for handset power amplifier development.
In view of the aforementioned problems of the prior art, the present invention provides a multi-level pulse modulated polar transmitter that includes an envelope signal input end for receiving input envelope signals; a constant-envelope modulated RF signal input end for receiving constant-envelope modulated RF input signals; a pulse modulation module for receiving the input envelope signals and generating a plurality of pulse modulation control signals of the input envelope signals; a plurality of signal modulation modules, each for receiving one of the constant-envelope modulated RF input signals and modulating the received one of the constant-envelope modulated RF input signals according to one of the multiple pulse modulation control signals, so as to generate pulsed-envelope modulated RF signals; and a plurality of power amplification modules, each for receiving the pulsed-envelope modulated RF signals carrying phase information, amplifying power of the pulsed-envelope modulated RF signals carrying phase information, and outputting the amplified pulsed-envelope modulated RF signals.
In another aspect of the present invention, a method of generating a multi-level pulsed-envelope modulated RF signal, comprising: receiving a plurality of corresponding pulse modulation control signals and constant-envelope modulated RF input signals by using a plurality of signal modulation modules; modulating the constant-envelope modulated RF input signals according to the pulse modulation control signals by using the signal modulation modules, so as to generate pulsed-envelope modulated RF signals carrying phase information; and combining the pulsed-envelope modulated RF signals generated by the signal modulation modules to generate multi-level pulse modulated RF signals.
In yet another aspect of the present invention, a method of generating multi-level pulse modulated RF signals, comprising: combining a plurality of pulsed-envelope modulated RF signals to generate multi-level pulse modulated RF signals.
Compared to the prior art, the multi-level pulse modulated polar transmitter of the present invention performs pulse modulation and signal combining processes with multiple pulse modulation control signals, to generate multi-level envelope signals. Therefore, the resolution is enhanced and the envelope path and the phase path can be easily synchronized.
The invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:
The following illustrative embodiments are provided to illustrate the disclosure of the present invention, these and other advantages and effects can be apparently understood by those in the art after reading the disclosure of this specification. The present invention can also be performed or applied by other different embodiments. The details of the specification may be on the basis of different points and applications, and numerous modifications and variations can be devised without departing from the spirit of the present invention.
Refer to
The envelope signal input end 103 receives envelope signals E(t). The constant-envelope modulated RF signal input end 105 receives constant-envelope modulated RF signals SCERF.
The pulse modulation module 102 receives and pulse modulates the envelope signals E(t) to generate a plurality of pulse modulation control signals E(n) that may have the same or different pulse widths, pulses of each of the pulse modulation control signals E(n) having the same or different phases.
The signal modulation modules 104 receive the constant-envelope modulated RF signals SCERF. Each of the signal modulation modules 104 modulates one of the constant-envelope modulated RF signals SCERF that it receives according to one of the multiple pulse modulation control signals E(n), and generates a pulsed-envelope modulated RF signal 104S that carries phase information in a pulsed envelope. Accordingly, each of the signal modulation modules 104 may perform a pulse modulation process on one of the constant-envelope modulated RF signals SCERF that it receives according to one of the multiple pulse modulation control signal E(n).
In the first embodiment, the signal modulation modules 104 may be implemented by various signal modulators, mixers, switches or logic circuits. Note that the multi-level pulse modulated polar transmitter 100 of the present invention may also employ other pulse modulation techniques similar to the pulse width modulation, such as the Σ-Δ modulation.
The power amplification modules 106 receive and amplify the pulsed-envelope modulated RF signals 104S output from the signal modulation modules 104, and output a plurality of output signals 106S with power being amplified.
Note that the envelope signals E(t) received at the envelope signal input end 103 are generated by RF input signals input at an RF input signal input end (not shown), and the constant-envelope modulated RF signals SCERF received at the constant-envelope modulated RF signal input ends 105 are also generated by the RF input signals input at the input signal input end (not shown). The RF input signals generate the envelope signals E(t) and constant-envelope modulated RF signals SCERF. The RF input signals may be in-phase quadrature signals (IQ modulated signals). Preferably, the envelope signals E(t) are the square root of a sum of squares of in-phase signals I(t) and quadrature signals Q(t) of the RF input signals, i.e., E(t)=√{square root over (I2(t)+Q2(t))}{square root over (I2(t)+Q2(t))}.
An embodiment of a polar transmitter of the present invention is described in accordance with
Refer to
The power splitter 201 receives constant-envelope modulated RF signals CERF of RF input signals, and splits them into a plurality of constant-envelope modulated RF signals SCERF that may have the same or different power. In the second embodiment, the total power of the constant-envelope modulated RF signals SCERF is approximately equal to the power of the constant-envelope modulated RF signals CERF. Preferably, a Wilkinson power splitter may be used to implement the power splitter 201, for splitting the power of the constant-envelope modulated RF signals CERF of the RF input signals into a plurality of output paths.
The pulse modulator 202 receives and performs a pulse modulation process on envelope signals E(t) of RF input signals, and generates a plurality of pulse modulation signals that may have different pulse widths and phases. The multiple pulse modulation signals are then transmitted to the corresponding signal modulators 204. Pulses of each of the pulse modulated signals may have different phases and widths. In the second embodiment, the pulse modulator 202 may be a pulse-width modulator, Σ-Δ modulator, or a modulator generating a plurality of digital signals, as shown in
The signal modulators 204 receive the corresponding constant-envelope modulated RF signals SCERF. Each of the signal modulators 204 modulates one of the constant-envelope modulated RF signals SCERF that it receives according to its corresponding pulse modulation signal, and generates pulsed-envelope modulated RF signals that carry phase information in a pulsed envelope. In the second embodiment, the Σ-Δ modulation technique, as well as the multiple pulse-width modulation technique, may be used to achieve the object of modulating the constant-envelope modulated RF signals SCERF. In the present invention, the signal modulator 204 may be implemented by transistors such as a single-pole single-throw CMOS switch, discrete circuit switching components, or any other circuit components that may achieve a signal modulation effect. For example, the signal modulators 204 may be implemented by various signal modulators, mixers, switches or logic circuits. A plurality of weighted RF power amplifiers 206 that are in the same size may be implemented in the second embodiment.
The RF power amplifiers 206 receive and amplify the pulsed-envelope modulated RF signals output from the signal modulators 204, and output a plurality of output signals with power being amplified. In the second embodiment, class-D, -E, -F, or other high-efficiency power amplifiers can be used to implement the RF power amplifiers 206. Also, the RF power amplifiers 206 may have the same weights, to achieve a better output effect.
The power combiner 208 receives and combines the output signals output from the RF power amplifiers 206, and generates and outputs multi-level pulse modulated RF output signals 208S. In the second embodiment, a Wilkinson power combiner is used to implement the power combiner 208, for combining the output signals, with the power being amplified, into a single output path, and outputting the multi-level pulse modulated RF output signals 208S.
The band-pass filter 210 receives the multi-level pulse modulated RF output signals 208S output from the power combiner 208. The band-pass filter 210 has a predetermined passband, such that the RF output signals pass only signal components that have a frequency within the predetermined frequency band, i.e., RFOUT.
In the second embodiment, a plurality of pulsed-envelope modulated RF signals may be combined to generate the multi-level pulse modulated RF output signals 208S.
A multi-level pulse modulated polar transmitter according to the present invention may be applied to a wireless mobile device for various standards. Refer to
Each of the signal modulation modules 304 modulates the received constant-envelope modulated RF signals according to one of the received pulse modulation control signals E(n)″ that receives, and generates corresponding pulsed-envelope modulated RF signals. The RF input signals applied to the circuit structure shown in
The present invention uses multiple pulse modulation control signals to resolve the problems of spurious emissions. RF output signals are restored by filtering the multi-level pulse modulated RF signals.
The present invention uses a plurality of multiple pulse modulation control signals to perform a pulse modulation process in order to enhance the bandwidth of a transmitter and reduce spurious noises. This property has a significant effect on removing the out-of-band emissions created by the pulse modulation.
Refer to
Refer to
Compared to the prior art, the multi-level pulse modulated polar transmitter of the present invention uses a plurality of pulse-envelope modulated RF signals to generate a multi-level pulse modulated RF signal carrying phase information within.
The foregoing descriptions of the detailed embodiments are only illustrated to disclose the features and functions of the present invention and not restrictive of the scope of the present invention. It should be understood to those in the art that all modifications and variations according to the spirit and principle in the disclosure of the present invention should fall within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 099121632 | Jul 2010 | TW | national |
