KR101603231B1 - Band-pass Delta Sigma Transmitter - Google Patents

Abstract

The present invention relates to a band-pass delta sigma signal transmitter, and more particularly, to a digital IF unit for converting an I / Q signal received from a base band into an IF signal. A multi-bit bandpass delta sigma modulator for sampling the IF signal and outputting a multi-bit quantized IF signal; An RF up-modulating unit for converting the multi-bit quantized IF signal into a multi-bit quantized RF signal; And a power amplifier for amplifying the multi-bit quantized RF signal.

Bandpass delta sigma, multi-bit, mobile communication, transmitter

Description

Band-pass Delta Sigma Transmitter [0002]

[0001] The present invention relates to a transmitter structure applied to a mobile communication system, and more particularly, to an RF amplifier with an envelope having a large Peak to Average Power Ratio (PAPR) The present invention relates to a transmitter that maximizes the efficiency of a power amplifier by applying a digital signal quantized with an N-level (multi-bit) RF signal. In order to achieve this, a band-pass delta sigma modulator which quantizes the RF signal into N-level is included. Since the quantized signal is N-level, this also has a certain PAPR value. The present invention relates to a transmitter that implements a high-efficiency power transmission system using an M-way Doherty power amplifier having a maximum efficiency in a digital signal size.

2. Description of the Related Art [0002] In recent mobile communication systems, a system having a multi-carrier modulation scheme such as OFDM (Orthogonal Frequency Division Multiplexing) has been developed in a CDMA (Code Division Multiple Access) system for high data transmission speed. For example, WIMAX, WIBro and 3G Long Term Evolution (LTE) systems employ OFDM modulation schemes. The OFDM system has a high peak to average power ratio (PAPR) of a transmission signal due to summation of carriers.

Therefore, various methods for increasing the transmission efficiency in a mobile communication system are being discussed. The EER (Envelop Elimination and Restoration) method of inputting a phase signal to a power amplifier and applying envelope information to a bias portion of a power amplifier using polar coordinates ) Method and an ET (Envelope Traking) method of modulating a bias of a power amplifier while applying a general complex I / Q signal instead of a phase signal as an input of the power amplifier.

The EER method maximizes the efficiency because an envelope-canceled signal is input to the power amplifier. However, it requires a broadband matching of the power amplifier due to band extension problem of the phase input signal. In addition, since the temporal error between the envelope information signal and the phase output signal is very sensitive, it is difficult to configure the hardware. Although theoretically efficiency is slightly reduced to compensate for this, an ET structure for modulating the bias of a power amplifier according to the size of an input signal has recently been attracting much attention, using a general complex I / Q upconversion signal as an input signal .

However, since both of the above two methods, that is, the EER method and the ET method, are required to modulate the baud to the envelope signal, the overall transmission efficiency is a value obtained by multiplying the efficiency of the bias modulator by the total efficiency of the power amplifier .

However, since both the EER and ET structures can not implement 70 to 80% of the efficiency of the bias modulator, it is difficult to implement the high-efficiency characteristics technically, and thus the EER and ET structures have limitations.

Meanwhile, another method of a high-efficiency transmission structure is a method of applying 1-bit band-pass delta-sigma processing to an RF up-modulated signal and applying it to a power amplifier. For this purpose, the bandpass delta sigma modulator has a drawback that it must operate at a clock speed four times faster than the RF carrier frequency, and the 1-bit digitized signal contains quantization noise, which is amplified together in the power amplifier And has a disadvantage of lowering the efficiency compared to the magnetic signal.

1 is a diagram illustrating a structure of a conventional high efficiency transmitter.

1, the polar converter 120 converts an I / Q signal output from the baseband, that is, the modem 110, into a polar coordinate system, and outputs envelope information to the bias modulator 140. FIG. If the signal output to the RF up-modulating unit 130 is a cosine / sine function, it operates as an EER system because it is a phase information signal. If it is an I / Q signal, it operates as an ET system. The RF up-converted signal is radiated to the antenna through a duplexer, a filter, and the like through the power amplifier 150.

The envelope information extracted from the polar converter 120 is input to the bias modulator 140 and amplified and modulated according to the bias value of the power amplifier 150 and then input to the drain or collector of the power amplifier 150. At this time, the low-frequency components of the envelope information are provided to the high-efficiency buck converter 160, the high-frequency components of the envelope information are provided to the linear Op-amp included in the bias modulator 140, And the voltage and current waveforms supplied to the bias of the voltage / current waveform become the desired envelope information.

However, as mentioned above, when the power consumed by the bias modulation unit 140 and the burst conversion unit 160 is large and the information is the wideband envelope information, the bias modulation unit 140 has to operate at a high speed, There is a problem that the efficiency of the power amplification system is lowered.

2 shows a structure of another high efficiency transmitter according to the prior art.

2, the I / Q signal output from the modem unit 210 is converted into an IF signal by the digital IF unit 220 and is converted into an RF carrier frequency by using the RF up-modulator 230 Thereafter, the 1-bit bandpass delta sigma modulator 240 digitizes the 1-bit signal into a 1-bit signal. The 1-bit digitized signal is input to the high-efficiency power amplifier 250 and is output, which is a method in which only the desired in-band signal is restored by the duplexer and the band-pass filter. In order to realize this, the 1-bit bandpass delta sigma modulator 240 has a disadvantage of performing a modulation operation at a clock speed at least four times faster than the RF frequency. For example, in order to digitize 1-bit RF frequency signals corresponding to 2 GHz, a sampling clock of 8 GHz is required.

Since the 1-bit digitized signal has already been quantized to 1-bit, the quantization noise is distributed over the entire band of the oversampling clock frequency, and the desired signal and the quantization noise signal are simultaneously applied to the power amplifier 250, Has a disadvantage in that the efficiency of a desired in-band signal is lowered.

SUMMARY OF THE INVENTION The present invention has been conceived to solve the above-described problems, and it is an object of the present invention to provide a multi-bit band pass delta sigma modulator which receives an IF signal, converts the signal into an N-level signal, Level delta sigma modulator by reducing the clock speed of the band-pass delta sigma modulator by outputting an N-level signal having an RF frequency by using an up-modulating unit, and inputting the N-level quantized digital signal to the power amplifier, And a signal transmitter.

It is another object of the present invention to provide a band-pass delta filter which ultimately transmits an N-level RF digital signal with high efficiency by using an M-way Doherty power amplifier having an optimum efficiency according to a characteristic distribution of an RF signal quantized at N- Sigma signal transmitter.

According to an aspect of the present invention, there is provided a digital IF receiver comprising: a digital IF unit for converting an I / Q signal received from a base band into an IF signal; A multi-bit bandpass delta sigma modulator for sampling the IF signal and outputting a multi-bit quantized IF signal; An RF up-modulating unit for converting the multi-bit quantized IF signal into a multi-bit quantized RF signal; And a power amplifier for amplifying the multi-bit quantized RF signal.

As described above, according to the present invention, it is possible to prevent a power amplifier from amplifying unnecessary quantization noise by providing a transmitter using a band-pass delta sigma modulator incorporating a multi-bit quantizer, It is possible to realize a wideband high efficiency power amplification system when applied to an actual base station terminal and also to miniaturize the system due to high efficiency.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

3 is a diagram illustrating a structure of a bandpass delta sigma signal transmitter according to an embodiment of the present invention.

3, the bandpass delta sigma signal transmitter 300 includes a modem 310, a digital IF unit 320, a multi-bit band pass delta sigma modulator A modulator 330, an RF up-converter 340, and a power amplifier 350. [

The digital IF unit 320 converts the I / Q signal received from the modem unit 310, i.e., the baseband, into an IF signal. Here, the IF frequency of the IF signal may be determined according to the system or may vary depending on the hardware configuration when the system is implemented, and is generally determined in the tens MHz band.

The multi-bit bandpass delta sigma modulator 330 samples the IF signal at a clock speed (4 * f _IF ) corresponding to four times the IF frequency. Here, the multi-bit bandpass delta sigma modulator 330 can be largely divided into a resonator and a quantizer, and the configuration types thereof can be classified into various groups. However, the technical feature of the present invention is that multi-bit bandpass delta sigma Since it is not in the modulator 330, detailed description related to the implementation of the multi-bit bandpass delta sigma modulator 330 will be omitted.

In the present invention, the multi-bit band pass delta sigma modulator 330 is characterized in that the quantizer outputs the input signal in multi-bit rather than 1-bit output. The sampled IF signal is quantized into multi-bits and quantization noise is generated. In the present invention, this quantization noise is spread up to half of the oversampling frequency.

When a conventional 1-bit quantizer is used, it seems that the input of the power amplifier processes only 1-bit "on" and "off" states to ensure high efficiency characteristics. However, Since the quantization noise generated by quantization with -bit is mixed together, the efficiency of the in-band signal at the final output of the power amplifier is reduced. Because the maximum power of the power amplifier is determined and the DC power consumption is determined accordingly, the efficiency is determined. When the 1-bit signals are all in-band signals, high efficiency operation occurs. However, When the quantized noise power is mixed, a loss as much as the quantized power with respect to the output signal is generated, and the overall in-band efficiency is reduced.

In order to solve such a problem, the present invention uses a multi-bit quantizer instead of a 1-bit quantizer as a means for minimizing quantization noise. When 1 bit is used, the quantization noise is reduced by 6dB. Therefore, when the minimum 2 bits (0, 1, 2, 3) state is used, the quantization noise is smaller by 6dB than when the 1-bit quantizer is used , So that the power amplifier does not output unnecessary quantization noise.

For example, when a bandpass delta sigma modulator using a 2-bit quantizer is used, the output of the multi-bit bandpass delta sigma modulator 330 shown in FIG. 3 corresponds to 0, 1, 2, And the sampling rate is the oversampling rate of the bandpass delta sigma modulator.

The RF up-modulating unit 340 converts the IF-signal quantized at the N-level into an RF signal. In detail, the RF up-modulating unit 340 converts an IF-signal quantized at the N-level into an RF signal at the IF-frequency and converts the signal quantized at the N-level into an N-level quantized signal at the RF carrier . A detailed description thereof will be given later with reference to FIG.

On the other hand, the RF signal quantized at the N-level is input to the power amplifier, and the RF signal quantized at the N-level has a peak-to-average value. That is, in order to drive a high efficiency power amplifier, a constant envelope signal (1-bit) without envelope information must be applied. Since the N-level quantized RF signal has PAPR, the power amplifier always saturates in the peak efficiency region It is impossible to operate in the state.

To solve this problem, a Doherty power amplifier is used as the power amplifier 350 in the present invention. The Doherty power amplifier combines a carrier power amplifier and a peak power amplifier. When two coupled structures (2-way) are used, the Doherty power amplifier has maximum efficiency at an output power as low as about 6dB at maximum output. A 3-way Doherty power amplifier When the structure is used, it has characteristics of maximum efficiency at an output power as low as about 9 dB.

Assuming that the N-level is quantized to 2 bits and the maximum size of the signal input to the power amplifier is 3, the signal size can be 0, 1, 2, and 3, Is 9 dB. If the 3-way Doherty power amplifier structure is applied, even if the 2-bit quantized signal has the PAPR, the power of the N-level quantized signal can be reduced without decreasing the efficiency The amplifier can output with high efficiency.

4 is a block diagram of a multi-bit band pass delta sigma modulator according to an embodiment of the present invention.

Referring to FIG. 4, the multi-bit band pass delta sigma modulator 330 includes quadratic resonators 410, 420, 430, and 440 and a multi-bit quantizer 450. In Fig. 4, the parameter values of a, b, c, and g are determined according to the size of the oversampling ratio and the input signal.

In addition, the multi-bit band pass delta sigma modulator 330 may further include a MUX and additional devices for outputting an IF signal quantized at the N-level.

5 is a diagram illustrating a configuration of an RF up-modulating unit 340 according to an embodiment of the present invention.

Referring to FIG. 5, the RF up-modulator 340 according to the present invention converts an IF-signal quantized at the N-level output from the multi-bit quantizer 450 of FIG. 4 into a plurality of AND gates 510, 520, 530) to an RF signal.

That is, the N-level quantized IF signal output from the multi-bit quantizer 450 is input to the plurality of AND gates 510, 520, and 530 on a stage-by-stage basis, and the RF signal generated in the frequency generator 540 And is output through the combiner 550. [ For example, if a quantized IF signal of 2 bits is to be input, the output of the multi-bit quantizer 450 is all stuck to "high", which is fed by a number of AND gates 510, 520, 530 The RF signal generated by the frequency generator 540 is multiplied by the AND function and output to the combiner 550, thereby generating a signal of size "3" at the RF frequency. The remaining 1 or 2 states are generated by the same algorithm, and the 0 state where no output is to be output is converted to the "0" state by the output of the multi-bit quantizer 450.

When the RF up-modulating unit 340 according to the present invention is used, an RF signal whose magnitude is quantized to an N-level at an RF frequency is generated. At this time, the N value of the N-level is determined considering both the channel width of the system, the oversampling ratio, the adjacent channel ratio of the final output, and the efficiency degradation characteristics of the high efficiency power amplifier.

Accordingly, the functions of the plurality of AND gates 510, 520, and 530 are made into an array according to the optimized N value, and the RF signal is also converted into the N-level quantized signal.

6 is a diagram illustrating a configuration of a power amplifier according to an embodiment of the present invention.

Referring to FIG. 6, the power amplifier 350 according to the present invention includes an M-way Doherty power amplifier, which includes a carrier power amplifier 610 for amplifying a carrier of a multi-bit quantized RF signal, A peak power amplifier 620 for amplifying the peak power, a quarter wave transformer 630 for power coupling, an offset line 640 for correcting the phase error occurring in the power coupling, and a 35-ohm transform line (650), and the like.

The power amplifier 350 according to the present invention further includes a phase error correction line 660 for compensating for a 90-degree phase error caused by incorporating the quarter-wave transformer 630 into the peak power amplifier 620.

The M-way Doherty power amplifier determines the M level according to the N value. That is, the optimum N value is determined according to the bandwidth of the system and the IF frequency, and if the probability distribution of the IF signal quantized at the N-level is determined, the maximum value M value having the maximum efficiency is determined.

7 is a diagram illustrating output characteristics of a multi-bit band pass delta sigma modulator when a quantizer having N = 3 (2 bits) is used in the present invention.

Referring to FIG. 7, (a) shows the output of the multi-bit bandpass delta-sigma modulator 330 on the time axis and shows that the output of the RF signal is quantized to 0, 1, , And it is found that the probability distribution is the largest in the "1" state.

(b) is a diagram showing the output of the multi-bit bandpass delta sigma modulator 330 as a probability function distribution on a state-by-state basis. As described above, it has the largest probability distribution in the " Quot; 3 "state. ≪ / RTI >

Therefore, by using Doherty power amplifiers with the best efficiency in the "1" state, the efficiency of the overall transmission system can be maximized.

8 is a view showing a frequency spectrum of an RF signal quantized in the present invention.

8A is a view showing a frequency spectrum of a quantized RF signal, FIG. 8B is an enlarged view of a frequency spectrum of -25 MHz to 25 MHz in FIG. 8A, and N = 3 (2 bits ), The adjacent channel interference ratio is lowered to 40 dBc or less. The quantization noise in the high frequency range of 50 MHz or more, that is, the spectrum due to noise shaping is filtered by the band-pass filter and the duplexer built in the final stage of the power amplifier.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

1 shows a structure of a conventional high efficiency transmitter,

2 shows a structure of another high efficiency transmitter according to the related art,

3 is a diagram illustrating a structure of a bandpass delta sigma signal transmitter according to an embodiment of the present invention,

4 is a diagram illustrating a configuration of a multi-bit band pass delta sigma modulator according to an embodiment of the present invention;

5 is a diagram illustrating a configuration of an RF up-modulating unit 340 according to an embodiment of the present invention.

6 is a diagram illustrating a configuration of a power amplifier according to an embodiment of the present invention.

7 is a diagram illustrating output characteristics of a multi-bit band pass delta sigma modulation unit when a quantizer having N = 3 (2 bits) is used in the present invention,

8 is a view showing a frequency spectrum of an RF signal quantized in the present invention.

Description of the Related Art

310: modem section 320: digital IF section

330: multi-bit band pass delta sigma modulator 340: RF up-modulator

350: Power amplifiers 410, 420, 430, 440: Resonators

450: Multi-bit quantizer 510, 520, 530: AND gate

540: Frequency generator 550: Coupler

610: Carrier power amplifier 620: Peak power amplifier

630: Quarter wave transformer 640: Offset line

650: 35 ohm transform line 660: phase error correction line

Claims (7)

A digital IF unit for converting an I / Q signal received from the baseband into an IF signal; A multi-bit bandpass delta sigma modulator for sampling the IF signal and outputting a multi-bit quantized IF signal; An RF up-modulating unit for converting the multi-bit quantized IF signal into a multi-bit quantized RF signal; And And a power amplifier for amplifying the multi-bit quantized RF signal, Wherein the multi-bit bandpass delta sigma modulator includes a fourth order resonator and a multi-bit quantizer, Wherein the RF up- A plurality of AND gates for mixing the multi-bit quantized IF signal output from the multi-bit quantizer and the RF signal generated by the frequency generator; And A combiner for combining and outputting the mixed signals; Band delta sigma signal transmitter. The method according to claim 1, Wherein the multi-bit bandpass delta-sigma modulator samples the IF signal at a clock speed corresponding to four times the IF frequency. delete delete The power amplifier according to claim 1, A carrier power amplifier for amplifying a carrier of the multi-bit quantized RF signal; A peak power amplifier amplifying a peak power of the multi-bit quantized RF signal; A quarter wave transformer for power coupling of the power amplifier; And An offset line for correcting a phase error occurring in power coupling of the power amplifier; Band delta sigma signal transmitter. The method according to claim 1, Wherein the power amplifier is a Doherty power amplifier. 6. The power amplifier according to claim 5, A phase error correction line for compensating for the 90-degree phase error caused by the quarter-wave transformer to the peak power amplifier; Band delta sigma signal transmitter.

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