KR20130065293A - Transmitter using piecewise delta-sigma modulation and signal generation method thereof - Google Patents

Abstract

PURPOSE: A transmitter using an interval delta-sigma modulation method and its signal generation method are provided to increase encoding efficiency or amplification efficiency. CONSTITUTION: A transmitter includes a polar converter (110), an interval delta-sigma modulator (120), a mixer (130) and a power amplifier (160). The polar converter separates an amplitude signal and a phase signal from a baseband signal. The interval delta-sigma modulator of 1-bit delta-sigma modulates or bypasses the amplitude signal according to a reference level. The mixer mixes the phase signal including an amplitude component and the envelope signal including a frequency component and transmits the phase signal to a DAC (140). The power amplifier amplifies the mixed signal. [Reference numerals] (110) Polar converter; (120) Interval delta-sigma modulator; (150) Up-converter; (160) Power amplifier; (AA) Status signal; (BB) Envelope signal; (CC) RF output

Description

Transmitter using interval delta-sigma modulation and signal generation method thereof {TRANSMITTER USING PIECEWISE DELTA-SIGMA MODULATION AND SIGNAL GENERATION METHOD THEREOF}

The present invention relates to a communication system, and more particularly, to a transmitter using a high efficiency delta-sigma modulation scheme and a signal generating method thereof.

Recently, a mobile communication system is a system of a multi-carrier modulation method such as orthogonal frequency division multiplexing (OFDM) in a conventional code division multiple access (CDMA) system for high data transmission speed. Is developing. For example, WIMAX, WIBro, and 3G Long Term Evolution (LTE) series communication systems adopt OFDM modulation. A disadvantage of the OFDM system is that the Peak to Average Power Ratio (PAPR) of the transmission signal is high due to the combination of a plurality of carriers. For this reason, what has emerged as a transmission method for increasing transmission efficiency is a method of separating and amplifying a phase signal and an envelope signal. That is, a phase signal is input to the switching power amplifier using polar coordinates, and an envelope signal is applied to the power amplifier. The envelope signal is digitized into a 1-bit signal for changes in level using sigma-delta modulation (SDM) or pulse width modulation (PWM) schemes. The envelope signal will then be encoded into a continuous envelope signal in the discontinuous envelope. In this case, the power amplifier always operates in the saturation region, which maximizes the efficiency of the power amplifier.

However, when using this 1-bit encoding method, there is a problem of lowering coding efficiency. Coding efficiency is expressed as a sum of noise generated when quantizing 1-bit and a desired signal, that is, a ratio of power of a desired signal to total power. When the general delta-sigma modulation method is used, quantization noise occurs because the time-varying envelope signal is quantized into a 1-bit pulse signal. Since the power amplifier must consume power to amplify this noise power, the efficiency of the final power amplifier is lowered.

SUMMARY OF THE INVENTION An object of the present invention is to provide a transmitter and a signal generation method thereof for providing a power amplifier using a period delta-sigma modulation scheme to solve the above problems.

According to an embodiment of the present invention, a transmitter includes a polar converter that separates an amplitude signal and a phase signal from an input signal, and an interval in which the amplitude signal is output as an envelope signal by 1-bit delta-sigma modulation or bypassing according to a reference level. A delta-sigma modulator, a mixer for mixing the phase signal and the envelope signal, and a power amplifier for amplifying the mixed signal.

According to an embodiment of the present invention, a method of generating a transmission signal includes: separating an input signal into a phase signal and an amplitude signal, detecting a level of the amplitude signal, and 1-bit of the amplitude signal according to the detected level Delta-sigma modulation or bypassing the amplitude signal to provide an envelope signal, and mixing and amplifying the phase signal and the envelope signal.

According to an embodiment of the present invention, a high coding efficiency and an amplifier efficiency are expected through a transmitter using a high efficiency delta-sigma modulation scheme and a signal generation method thereof.

1 is a block diagram schematically illustrating a transmitter according to an exemplary embodiment of the present invention.
FIG. 2 is a block diagram illustrating an exemplary configuration of the interval delta-sigma modulator of FIG. 1.
3 is a waveform diagram sequentially illustrating the operation of the interval delta-sigma modulator of FIG. 2.
4 is a diagram illustrating a waveform of an output signal by the interval delta-sigma modulator of FIG. 2.
5 is a flowchart illustrating a method of generating an envelope signal according to an exemplary embodiment of the present invention.
6 is a graph showing a change in coding efficiency according to a reference value K of the interval delta-sigma modulator of the present invention.
7 is a graph showing the frequency spectrum of the envelope signal of the present invention.
8 is a graph showing the efficiency of a power amplifier using a period delta-sigma modulator according to an embodiment of the present invention.

The foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the claimed invention. Therefore, the present invention is not limited to the embodiments described herein and may be embodied in other forms. The embodiments disclosed herein are provided so that the disclosure can be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In this specification, when it is mentioned that a certain element includes an element, it means that it may further include other elements. In addition, each embodiment described and illustrated herein includes its complementary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram schematically illustrating a structure of a transmitter according to an exemplary embodiment of the present invention. Referring to FIG. 1, the transmitter 100 includes a polar converter 110, a period delta-sigma modulator 120, a mixer 130, a DAC 140, an up-converter 150, and a power amplifier 160. Include.

The polar converter 110 generates a phase signal Φ (t) and an amplitude signal a (t) with reference to the input mutually orthogonal in-phase signal I (t) and quadrature signal Q (t). The polar converter 110 processes the input in-phase signal I (t) and quadrature signal Q (t) to generate a phase and an amplitude including information. The polar converter 110 may include, for example, a processor that performs a CORDIC algorithm (COordinate Rotation DIgital Computer Algorithm). The CORDIC algorithm is a hardware-optimized algorithm that allows complex and diverse mathematical operations to be implemented in a simple structure of bitwise shift and addition (no multiplier).

Interval delta-sigma modulator 120 modulates amplitude signal a (t) from polar converter 110 into envelope signal E (t). The interval delta-sigma modulator 120 bypasses the amplitude signal a (t) according to a reference level or performs lowpass delta-sigma modulation. For example, the interval delta-sigma modulator 120 outputs the delta-sigma modulation without the delta-sigma modulation when the level of the amplitude signal a (t) is higher than the reference level. The interval delta-sigma modulator 120 performs delta-sigma modulation on the amplitude signal a (t) when the level of the amplitude signal a (t) is less than or equal to the reference level. Therefore, the interval delta-sigma modulator 120 performs delta-sigma modulation according to the level of the amplitude signal a (t). Interval delta-sigma modulator 120 may perform normalization on the amplitude signal a (t) to select a reference level.

By the mixer 130, the envelope signal E (t) and the phase signal Φ (t) of the present invention are mixed. The mixer 130 may combine the amplitude component included in the envelope signal E (t) with the frequency component included in the phase signal Φ (t). The mixed signal of the envelope signal E (t) and the phase signal Φ (t) is transmitted to the digital-to-analog converter 140. The digital-to-analog converter 140 upconverts the mixed signal of the envelope signal E (t) and the phase signal Φ (t) to the RF band. The up-converted signal is amplified by the power amplifier 160.

In the above, the transmitter structure of the present invention for performing selective delta-sigma modulation according to the level of the amplitude signal a (t) has been briefly described. Quantization noise can be reduced for an envelope signal higher than a reference level through the interval delta-sigma modulator 120 of the present invention. This is because amplitude signals higher than the reference level are bypassed without quantization processing. Therefore, it is possible to reduce the noise power generated when amplifying the signal included in the quantization noise, and to increase the coding efficiency accordingly. In addition, it can be applied to a C-class power amplifier operating at a low bias in accordance with the selection of the reference level, it can be applied as a high efficiency power amplifier.

In addition, if the scheme of regenerating the envelope using the interval delta-sigma modulation method of the present invention can achieve high coding efficiency and amplification efficiency, a duplexer is used instead of a bandpass filter in the subsequent stage of the power amplifier 160. Can be provided. Therefore, by applying the embodiment of the present invention, it is possible to configure a transmitter having a simple structure.

FIG. 2 is a block diagram exemplarily illustrating the interval delta-sigma modulator of FIG. 1. 2, the interval delta-sigma modulator 120 includes a level selection delta-sigma modulator 121, a level selector 122, and an adder 123.

The level selection delta-sigma modulator 121 performs delta-sigma modulation only on the amplitude signal a (t) below the input selected level. The level selection delta-sigma modulator 121 performs selective delta-sigma modulation with reference to a clock of the provided reference level 1 / K and frequency fs. For example, the level select delta-sigma modulator 121 performs 1-bit delta-sigma modulation on a signal at a level equal to or lower than 1 / K of the level of the normalized amplitude signal a (t). The level select delta-sigma modulator 121 then stops 1-bit delta-sigma modulation for the signal higher than l / K of the level of the normalized amplitude signal a (t). The signal output by the level select delta-sigma modulator 121 corresponds to the first envelope signal E1 (t). Here, 1 / K at the level of the normalized amplitude signal a (t) is referred to as a reference level. K, which defines the reference level, will be referred to as a reference value.

The level selector 122 cuts out the amplitude signal a (t) below the reference level 1 / K and outputs only the amplitude signal a (t) above the reference level 1 / K. For example, the level selector 122 blocks a signal having a level equal to or lower than the reference level l / K among the levels of the normalized amplitude signal a (t). The level selector 122 outputs a signal higher than the reference level l / K among the levels of the normalized amplitude signal a (t). The signal output by the level selector 122 corresponds to the second envelope signal E2 (t).

The adder 123 adds the first envelope signal E1 (t) output from the level select delta-sigma modulator 121 and the second envelope signal E2 (t) output from the level selector 122. For example, the adder 123 is a first envelope signal E1 (continuous signal output from the level select delta-sigma modulator 121 for a signal equal to or greater than the reference level l / K among the levels of the normalized amplitude signal a (t). will print t). And the adder 123 is a 1-bit delta-sigma modulated second envelope signal E2 (t) provided from the level selector 122 for a signal lower than the reference level l / K among the levels of the normalized amplitude signal a (t). Will print The envelope signal E (t) finally output by the adder 123 will output a signal higher than the reference level as a continuous signal, and a signal below the reference level will be output as a 1-bit delta-sigma modulated digital signal.

3 is a timing diagram illustrating the function of the interval delta-sigma modulator of FIG. 2. Referring to FIG. 3, the waveform diagram (a) shows a waveform obtained by normalizing the input amplitude signal a (t). The waveform diagram (b) shows the first envelope signal E1 (t), the waveform diagram (c) shows the second envelope signal E2 (t), and the waveform diagram (c) shows the envelope signal E (t) that is output.

Referring first to the waveform diagram (a), it shows a normalized amplitude signal a (t). Normalization can be performed by dividing the amplitude signal a (t) by the absolute value a (t). Normalized amplitude signals will not have a maximum value of '1'. Then, the reference value K defining the reference level of the level selection delta-sigma modulator 121 (see FIG. 2) and the level selector 122 (see FIG. 2) is set. Here, for example, it is assumed that the reference value K is '3'. Therefore, the reference level is '1/3'. The level select delta-sigma modulator 121 and the level selector 122 will operate based on '1/3'.

The waveform diagram (b) shows the waveform of the first envelope signal E1 (t). The level select delta-sigma modulator 121 blocks amplitude signals higher than the reference level '1/3'. The level selection delta-sigma modulator 121 may perform 1-bit delta-sigma modulation on an amplitude signal having a level below the reference level '1/3'. When the level selection delta-sigma modulator 121 performs the delta-sigma modulation on the amplitude signal a (t) through sampling and quantization, the level change is only changed for values having a level below the reference level '1/3'. Will record the information. This is a 1-bit delta-sigma modulation operation. The change in level will be transferred to the 1-bit data stream.

The waveform diagram (c) shows the waveform of the second envelope signal E2 (t). The level selector 122 blocks when the level of the normalized amplitude signal a (t) is equal to or less than the reference level '1/3'. The level selector 122 bypasses the amplitude signal a (t) having a level higher than the reference level '1/3' without additional modulation. As shown in the waveform diagram (c), only the continuous signals of the second envelope signal E2 (t) higher than the reference level '1/3' are shown.

The waveform diagram (d) is a waveform diagram showing the envelope signal E (t) in which the first envelope signal E1 (t) and the second envelope signal E2 (t) are combined. The envelope signal E (t) is a signal in which envelope signals of different signaling methods are combined based on the reference level '1 / K'. However, it is possible to increase the coding efficiency by the appropriate reference value 'K' by the envelope signal E (t) in this manner.

4 is a waveform diagram showing an exemplary form of the envelope signal E (t) of the present invention. Referring to FIG. 4, the envelope signal E (t) is output as a 1-bit delta-sigma modulated signal in a signal level section below the reference level and as a continuous signal in a signal level section above the reference level. In FIG. 4, the characteristic of the envelope signal E (t) will be described by taking the case where the reference value K is 3 as an example.

By the interval delta-sigma modulator 120 of the present invention, the amplitude signal a (t) at a level below the reference level '1/3' is regenerated into a 1-bit digital signal. In other words, a level less than '1/3' in the original amplitude signal will be coded with a value of either level '0' or level '1/3' by interval delta-sigma modulation. For level '0' where the amplitude signal a (t) at a level lower than the reference level '1/3' is encoded, this means that there is little input signal at the power amplifier 160. Therefore, the power amplifier 160 only needs to amplify the envelope signal E (t) equal to or greater than '1/3' level. This means you do not have to use class AB or class A power amplifiers that provide amplifier capability for all amplitude levels. This means that a Class-C amplifier operating at a low power amplifier bias can be used as a power amplifier. Class C amplifiers use a very low bias, which means they are not amplified at levels with small envelope sizes, which can distort the signal. However, according to the coding method used in the present invention, an envelope signal having a reference level '1/3' or less is modulated with level information of '1/3' and '0'. Therefore, in the transmitter of the present invention, a class-C amplifier capable of operating at a level of '1/3' may be used.

5 is a flowchart briefly illustrating a modulation method according to an exemplary embodiment of the present invention. Referring to FIG. 5, the interval delta-sigma modulator 120 of the present invention bypasses the envelope signal to 1-bit delta-sigma modulation or a continuous signal according to a reference level. In more detail,

In step S110, the interval delta-sigma modulator 120 receives the amplitude signal a (t) from the polar converter 110. Here, it will be appreciated that the step of receiving the amplitude signal a (t) at the interval delta-sigma modulator 120 may include a sampling and quantization process for the amplitude signal.

In step S120, the interval delta-sigma modulator 120 normalizes the amplitude signal a (t). For normalization to the amplitude signal a (t) the amplitude signal a (t) can be divided by the absolute value | a (t) |. Normalized amplitude signals will not have a maximum value of '1'.

In step S130, the interval delta-sigma modulator 120 detects whether the level of the normalized amplitude signal is below or above the reference level 1 / K. If the level of the normalized amplitude signal is below the reference level 1 / K, the procedure moves to step S140 for 1-bit delta-sigma modulation. On the other hand, if the level of the normalized amplitude signal is higher than the reference level 1 / K, the procedure moves to step S150 for bypassing the continuous signal.

In step S140, the level selection delta-sigma modulator 121 (see FIG. 2) of the interval delta-sigma modulator 120 performs 1-bit delta-sigma modulation on the level of the input amplitude signal a (t). That is, the level select delta-sigma modulator 121 will output the 1-bit delta-sigma modulated first envelope signal E1 (t).

In step S150, the level selector 122 (see Fig. 2) will selectively output only the normalized amplitude signal a (t) of the signal interval higher than the reference level 1 / K. That is, the level selector 122 selects only a signal having a level higher than 1 / K and outputs the second envelope signal E2 (t).

In step S160, the adder 123 (see FIG. 2) receives the first envelope signal E1 (t) output from the level select delta-sigma modulator 121 and the second envelope signal E2 (t) output from the level selector 122. Add. For example, the adder 123 is a first envelope signal E1 (t) which is a continuous signal output from the level select delta-sigma modulator 121 for a signal of l / K or more among the levels of the normalized amplitude signal a (t). Will print And the adder 123 is a 1-bit delta-sigma modulated second envelope signal E2 (t) provided from the level selector 122 for a signal lower than the reference level l / K among the levels of the normalized amplitude signal a (t). Will print The envelope signal E (t) finally output by the adder 123 will output a signal higher than the reference level as a continuous signal, and a signal below the reference level will be output as a 1-bit delta-sigma modulated digital signal.

6 is a graph showing an effect according to an embodiment of the present invention. Referring to FIG. 6, the coding efficiency of the transmitter increases in a certain interval as the reference value K increases. By using such interval delta-sigma modulation, it is possible to exhibit higher coding efficiency characteristics than the method of delta-sigma modulation all amplitude signals. This is because the amount of quantization noise generated in the delta-sigma modulation step during the period delta-sigma modulation of the present invention is low. The increase in coding efficiency changes with the reference value K. Coding efficiency for the change in the reference value K gradually increases until the threshold is reached, as shown. When the reference value K is 1, it is only about 45% lower than the coding efficiency of a Doherty amplifier using typical delta-sigma modulation. However, as the reference value K increases, the coding efficiency increases in the form of a logarithmic function. Here, it can be seen that as the reference value K increases to 2 or more, average drain efficiency and average channel efficiency of the power amplifier decrease. However, despite this decrease in efficiency, it shows an amplifier efficiency of about 5% or more compared to a typical Doherty amplifier at the point where the reference value K is 5.8.

However, if the reference value K becomes too large, the signal processed by 1-bit delta-sigma modulation in the amplitude signal almost disappears. In this case, therefore, a general envelope signal is applied to the power amplifier 160, so that it is difficult to expect an improvement in amplification efficiency. Therefore, it is important to determine the appropriate reference value K. The optimized reference value K may be determined according to the efficiency of the power amplifier 160 itself and the characteristics of the signal used (eg, PAPR). As an example, for 3G LTE signals with a PAPR of 8.5 dB, the Doherty power amplifier exhibits optimal efficiency at a reference value K of about 5-6. And, for a general switching power amplifier or a C-class bias power amplifier, it can be estimated that the reference value K of 3 to 3.5 provides the optimum efficiency.

7 is a graph showing a frequency spectrum of a transmission signal according to an embodiment of the present invention. Referring to FIG. 7, it can be seen that when the reference value K is set to 3, the noise power located at the outside of the center frequency is relatively low. This effect means the reduction of quantization noise by delta-sigma modulation of the present invention.

8 is a graph illustrating encoding efficiency of power amplifiers according to an embodiment of the present invention. Referring to FIG. 8, amplification efficiencies of a B-class power amplifier using a general delta-sigma modulation technique and a C-class power amplifier using a delta-sigma modulation technique of the present invention are shown. If you set the amplifier's output backoff to about 6dB, then at this point, a B-class power amplifier is about 35% efficient. If the power amplifier is configured with an output power backoff of about 6 dB, then at this point, a C-class power amplifier using the interval delta-sigma modulation technique is about 40.2% efficient. Therefore, when using the C-class power amplifier to apply the modulation technique of the present invention can be expected to increase the efficiency of about 7 ~ 10%.

As a result, the modulation technique of the present invention enables the use of a C-class or Doherty power amplifier with high efficiency without using a general AB-class or B-class power amplifier. Therefore, an efficiency increase of about 5 to 10% can be expected. In addition, the interval delta-sigma modulation scheme of the present invention is simpler than the general delta-sigma modulation scheme and has excellent coding efficiency, and thus does not amplify unnecessary noise.

So far I looked at the center of the preferred embodiment for the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover the modifications and variations of this invention provided they fall within the scope of the following claims and equivalents.

110: Polar Converter
120: interval delta-sigma modulator
121: Level Selection Sigma-Delta Modulator
122: level selector
123: adder
130: mixer
140: DAC
150: up-converter
160: power amplifier

Claims (12)

A polar converter separating the amplitude and phase signals from the baseband signal;
A period delta-sigma modulator for outputting the amplitude signal as an envelope signal by 1-bit delta-sigma modulation or bypassing the amplitude signal;
A mixer for mixing the phase signal and the envelope signal; And
And a power amplifier for amplifying the mixed signal. The method of claim 1,
The interval delta-sigma modulator bypasses the amplitude signal if the level of the amplitude signal is higher than the reference level. 3. The method of claim 2,
And the interval delta-sigma modulator outputs the amplitude signal by 1-bit delta-sigma modulation when the level of the amplitude signal is equal to or lower than the reference level. The method of claim 1,
The reference level is determined in consideration of the coding efficiency of the interval delta-sigma modulator and the amplification efficiency of the power amplifier. The method of claim 1,
Wherein said power amplifier is a class C biased power amplifier or a Doherty amplifier. The method of claim 1,
A digital-analog converter for converting the output of the mixer into analog form; And
And an up-converter for upconverting the signal output from the digital-analog converter to an RF band. The method of claim 1,
The interval delta-sigma modulator,
A level selection delta-sigma modulator for providing only a 1-bit delta sigma modulation of the amplitude signal having a level equal to or lower than the reference level as a first envelope signal;
A level selector for selectively outputting only the amplitude signal section higher than the reference level, and blocking the amplitude signal section equal to or lower than the reference level to provide as a second envelope signal; And
And an adder that adds the first envelope signal and the second envelope signal to provide the envelope signal. Separating the baseband signal into a phase signal and an amplitude signal;
Detecting a level of the amplitude signal;
Providing the amplitude signal as an envelope signal by 1-bit delta-sigma modulation or bypassing the amplitude signal according to the detected level; And
And amplifying the mixed phase signal and the envelope signal. The method of claim 8,
Normalizing the level of the amplitude signal. The method of claim 9,
Comparing the level of the normalized amplitude signal with a reference level. 11. The method of claim 10,
In the step of providing the envelope signal,
And if the level of the normalized amplitude signal is higher than the reference level, the amplitude signal is bypassed. 11. The method of claim 10,
In the step of providing the envelope signal,
And performing 1-bit delta-sigma modulation on the amplitude signal when the level of the normalized amplitude signal is equal to or lower than the reference level.

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