KR20110068605A - Band-pass delta sigma transmitter - Google Patents

Abstract

PURPOSE: A bandpass delta sigma signal transmitter which uses a band pass delta signal modulator is provided to prevent the unnecessary quantization noise of a power amplifier. CONSTITUTION: A digital IF(Intermediate Frequency) unit(320) converts an I/Q signal which is received from a baseband to an IF signal. A multi-bit band pass delta sigma modulating unit(330) outputs the IF signal through the sampling of the IF signal. An RF up converter(340) converts the quantized IF signal into the quantized RF signal. A power amplifier(350) amplifies the quantized RF signal.

Description

Band-pass Delta Sigma Transmitter

The present invention relates to a transmitter structure applied to a mobile communication system, and more particularly, to apply an RF complex signal having an envelope having a large peak to average power ratio (PAPR) to an input of a power amplifier for high efficiency power amplification. Rather, the present invention relates to a transmitter that maximizes the efficiency of a power amplifier by applying a digital signal in which an RF signal is quantized to N-level (multi-bit). To this end, it includes a band pass delta sigma modulator that quantizes the RF signal to N-level, and since it is quantized to N-level, it also has some PAPR value, so the most signal out of N-level signal probability distribution is output. The present invention relates to a transmitter for implementing a high-efficiency power transmission system using an M-way Doherty power amplifier having a maximum efficiency at a digital signal level.

Recently, a mobile communication system has been developed from a conventional code division multiple access (CDMA) based system for a high data transmission rate to a system having a multi-carrier modulation scheme such as orthogonal frequency division multiplexing (OFDM). For example, WIMAX, WIBro, and 3G Long Term Evolution (LTE) series systems employ OFDM modulation. Such an OFDM system has a disadvantage in that a peak to average power ratio (PAPR) of a transmission signal is high due to summation of carriers.

Therefore, various methods for increasing the transmission efficiency in a mobile communication system have been discussed. The EER (Envelop Elimination and Restoration), which uses a polar coordinate to input a phase signal to the power amplifier and applies envelope information to the bias portion of the power amplifier, has been discussed. And an Envelop Traking (ET) method that modulates the bias of the power amplifier while applying a typical Complex I / Q signal rather than a phase signal as the input of the power amplifier.

The EER method maximizes efficiency because a signal without an envelope is input as an input of a power amplifier, but has a disadvantage in that broadband matching of the power amplifier is required due to a band extension problem of a 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. In order to compensate for this, the efficiency is slightly reduced, but the ET structure that uses a general Complex I / Q up-conversion signal as the input signal and modulates the bias of the power amplifier according to the magnitude of the input signal has received much attention recently. .

However, since the two methods, that is, the EER method and the ET method, must modulate the bias according to the envelope signal, the overall transmission efficiency is a value obtained by multiplying the efficiency of the bias modulator by the overall efficiency of the power amplifier as shown in Equation 1 below. Indicates.

However, both the EER and ET structures have limitations of the EER and ET structures because they can only implement 70-80% of the efficiency of the bias modulator and are difficult to technically implement high efficiency characteristics.

On the other hand, another method of the high efficiency transmission structure is a method of applying a 1-bit band pass delta sigma to the RF amplifier to the power amplifier. The bandpass delta sigma modulator has the disadvantage of operating at a clock speed four times faster than the RF carrier frequency, and the 1-bit digitized signal contains quantization noise, which is then amplified together in the power amplifier. It has the disadvantage of lowering the efficiency compared to the magnetic signal.

1 is a view showing the structure of a high efficiency transmitter according to the prior art.

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

The envelope information extracted by the polar converter 120 is input to the bias modulator 140, 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. In this case, the low frequency component of the envelope information is provided to the buck converter 160 having high efficiency, and the high frequency component of the envelope information is provided to the linear op-amp included in the bias modulator 140 to provide the final power amplifier 150. The voltage and current waveforms supplied to the bias of become the desired envelope information.

However, as mentioned above, when the power consumption of the bias modulator 140 and the buck converter 160 is large, and also wide envelope information, the bias modulator 140 may operate at a high speed. Since there is a characteristic to consume more, there is a problem to lower the efficiency of the power amplification system.

2 is a view showing the structure of another high efficiency transmitter according to the prior art.

Referring to FIG. 2, the I / Q signal output from the modem unit 210 is converted into an IF signal by the digital IF unit 220, which is up-converted to an RF carrier frequency using the RF up-modulator 230. Then, it is digitized into a 1-bit signal using the 1-bit band pass delta sigma modulator 240. The 1-bit digitized signal is input to the high efficiency power amplifier 250 and outputted, 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 implement this, the 1-bit band pass delta sigma modulator 240 has a disadvantage that the modulation operation must be performed at a clock speed that is at least four times faster than the RF frequency. For example, in order to 1-bit digitization of an RF frequency signal corresponding to 2 GHz, a sampling clock of 8 GHz is required.

In addition, since the 1-bit digitized signal is already 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 so that the final signal is finally obtained. Has the disadvantage of lowering the efficiency of the desired in-band signal.

The present invention has been made in order to solve the above problems, and receives an IF signal and processes it with a multi-bit band pass delta sigma modulator, converts the signal to N-level, and then RF upconverts it. Band-pass delta sigma reduces the clock speed of the band-pass delta sigma modulator by outputting it as an N-level signal having an RF frequency by using an up-modulation section, and inputs a digital signal quantized in N-level to the power amplifier to provide a band pass delta sigma The object is to provide a signal transmitter.

Another object of the present invention is to use a M-way Doherty power amplifier having an optimal efficiency according to the characteristic distribution of the N-level quantized RF signal, thereby finally band band delta for transmitting N-level RF digital signal with high efficiency Provides a sigma signal transmitter.

The present invention for achieving the above object, Digital IF unit for converting the I / Q signal received from the base band to the IF signal; A multi-bit band pass delta sigma modulator for sampling the IF signal and outputting a multi-bit quantized IF signal; An RF up-modulator 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, by providing a transmitter using a band pass delta sigma modulator with a multi-bit quantizer, it is possible to prevent the power amplifier from amplifying unnecessary quantization noise, The high efficiency degradation factor can be eliminated, and when applied to a base station terminal, it is possible not only to implement a broadband high efficiency power amplification system, but also to bring down the size of the system due to the high efficiency.

Hereinafter, an embodiment 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 illustrates a structure of a band pass delta sigma signal transmitter according to an embodiment of the present invention.

Referring to FIG. 3, the band pass delta sigma signal transmitter 300 according to the present invention includes a modem unit 310, a digital IF unit 320, and a multi-bit band pass delta sigma modulator. A modulator 330, an RF up converter 340, a power amplifier 350, and the like.

The digital IF unit 320 converts the I / Q signal received from the modem unit 310, that is, the baseband, into an IF signal. In this case, the IF frequency of the IF signal may be determined for each system or may vary depending on a hardware configuration when the system is implemented, and is generally determined in the tens of MHz bands.

The multi-bit band pass 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 band pass delta sigma modulator 330 may be largely divided into a resonator and a quantizer, and its configuration type may also be classified into various groups, but the technical features of the present invention are multi-bit band pass delta sigma. Since it is not present in the modulator 330, a detailed description related to the implementation of the multi-bit band pass 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 outputting the input signal in 1-bit. As the sampled IF signal is quantized in multi-bits, quantization noise is generated. In the present invention, the quantization noise is spread to half of the oversampling frequency.

When the conventional 1-bit quantizer is used, it seems that the input of the power amplifier processes only the 1-bit "on" and "off" states to guarantee high efficiency characteristics, but the actual 1-bit signal includes an in-band signal and 1 The quantization noise produced by quantization at -bit is mixed together, reducing the efficiency of the in-band signal at the power amplifier's final output. Because the maximum output 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, but the 1-bit signals When quantized noise power is mixed, there is a loss of quantization power relative to the output signal, which reduces the overall in-band efficiency.

In order to solve this problem, the present invention uses a multi-bit quantizer instead of a 1-bit quantizer as a method for minimizing quantization noise. When using 1 bit more, the quantization noise generated decreases by 6dB. When using at least 2 bit (0, 1, 2, 3) state, the quantization noise is 6dB smaller than using 1-bit quantizer. As a result, the power amplifier does not output unnecessary quantization noise.

For example, when a band pass delta sigma modulator using a 2-bit quantizer is used, the outputs of the multi-bit band pass delta sigma modulator 330 shown in FIG. 3 correspond to 0, 1, 2, and 3. The sampling rate is the over sampling rate of the band pass delta sigma modulator.

The RF uplink modulator 340 converts the N-level quantized IF signal into an RF signal. In detail, the RF uplink modulator 340 muxes the N-level quantized IF signal with the RF carrier to convert the quantized signal from the IF frequency to the N-level quantized signal from the RF carrier to the N-level quantized signal. Do this. Detailed description thereof will be described later with reference to FIG. 5.

On the other hand, the N-level quantized RF signal is input to the power amplifier and output, and the N-level quantized RF signal also has a PAPR since it has a magnitude of the peak-to-average value. That is, a constant envelope signal (1-bit) without envelope information must be applied to drive a high efficiency power amplifier. Since an N-level quantized RF signal has a PAPR, the power amplifier is always saturated in the peak efficiency region. It will not work in a state.

In order to solve this problem, the present invention uses a Doherty power amplifier as the power amplifier 350. The Doherty power amplifier combines a carrier power amplifier and a peak power amplifier to achieve maximum efficiency at output power as small as about 6 dB at maximum output when two coupling schemes (2-way) are used. When the structure is used, it has a characteristic of maximum efficiency at an output power of about 9 dB.

Assuming that the N-level is quantized to 2 bits, and assuming that the maximum magnitude of the signal input to the power amplifier is 3, the magnitude of the signal may be 0,1.2.3, and the maximum magnitude of 3 is 1 Power magnitude up to 9dB. Therefore, if the N-level quantized signal occurs most frequently in the section of “1” in the probability distribution, when the 3-way Doherty power amplifier structure is applied, even if the 2-bit quantized signal has a PAPR, the power is not reduced. The amplifier can output with high efficiency.

4 is a diagram illustrating a configuration 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 a fourth-order resonators 410, 420, 430, and 440 and a multi-bit quantizer 450. In FIG. 4, parameter values of a, b, c, and g are determined according to the oversampling ratio and the magnitude of the input signal.

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

5 is a diagram illustrating a configuration of an RF uplink modulator 340 according to an embodiment of the present invention.

Referring to FIG. 5, the RF uplink modulator 340 according to the present invention receives an N-level quantized IF signal output from the multi-bit quantizer 450 of FIG. 4. Up-converting to the RF signal using 530.

That is, the N-level quantized IF signal output from the multi-bit quantizer 450 is input to a plurality of AND gates 510, 520, and 530 per stage, and the RF signal generated by the frequency generator 540 is different from the IF signal. It is mixed and output through the combiner 550. For example, assuming that a 2-bit quantized IF signal is input, the outputs of the multi-bit quantizer 450 are all "high", which is caused by multiple AND gates 510, 520, 530. The RF signal generated by the frequency generator 540 is multiplied by an AND function and output to the combiner 550, thereby generating a signal having a magnitude of "3" at the RF frequency. The remaining 1 and 2 states are also generated by the same algorithm, and the 0 state, which should be no output, is converted to the "0" state of the multi-bit quantizer 450.

Using the RF up-modulator 340 according to the present invention, an RF signal quantized to an N-level at an RF frequency is generated. In this case, the N value of the N-level is determined in consideration of the channel width of the system, the oversampling ratio, the adjacent channel ratio of the final output, and the efficiency deterioration characteristics of the high efficiency power amplifier.

Thus, the function of the multiple AND gates 510, 520, 530 is an array according to the optimized N value, and the RF signal is also converted to an N-level quantized signal.

6 is a view showing the configuration of a power amplifier according to an embodiment of the present invention.

6, the power amplifier 350 according to the present invention is a M-way Doherty power amplifier, a carrier power amplifier 610 for amplifying a carrier of a multi-bit quantized RF signal, a multi-bit quantized RF signal Peak power amplification unit 620 for amplifying peak power, quarter wave transformer 630 for power coupling, offset line 640 for correcting phase error generated during power coupling, and 35 ohm transform line for 50 ohm matching 650 and the like.

In addition, the power amplifier 350 according to the present invention further includes a phase error correction line 660 that compensates for the 90-degree phase error generated by embedding the quarter wave transformer 630 with the peak power amplifier 620.

For M-way Doherty power amplifiers, the M level is determined by the N value. That is, if the optimal N value is determined according to the bandwidth and the IF frequency of the system, and the probability distribution of the IF signal quantized to the N-level is determined, the M value having the maximum efficiency is determined to the maximum probability value.

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

Referring to FIG. 7, (a) shows the output of the multi-bit band pass delta sigma modulator 330 on the time axis, and it can be seen that the output of the RF signal is quantized to 0, 1, 2, and 3. It can be seen that the most likely distribution in the "1" state.

(b) is a diagram showing the probability function distribution for each state of the output of the multi-bit band pass delta sigma modulator 330, and as described above, has the most probability distribution in the "1" state, "2", It can be seen that there is a small probability distribution in the "3" state.

Thus, by using the most efficient Doherty power amplifier in the "1" state, the efficiency of the overall transmission system can be maximized.

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

Referring to FIG. 8, (a) is a diagram showing a frequency spectrum of a quantized RF signal, (b) is a diagram showing an enlarged frequency spectrum between -25 MHz and 25 MHz in (a), and N = 3 (2 bit). It can be seen that when the quantizer () is used, the adjacent channel interference ratio is lowered to 40 dBc or less. Quantization noise in the high frequency region above 50 MHz, ie the spectrum due to noise shaping, is filtered by a band pass filter and duplexer built into 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 not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a view showing the structure of a high efficiency transmitter according to the prior art;

2 is a view showing the structure of another high-efficiency transmitter according to the prior art;

3 is a diagram illustrating a structure of a band pass 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 uplink modulator 340 according to an embodiment of the present invention;

6 is a view showing the configuration of a power amplifier according to an embodiment of the present invention;

7 is a view showing the output characteristics of the multi-bit band pass delta sigma modulator when using a quantizer having N = 3 (2 bit) in the present invention,

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

<Description of Symbols for Main Parts of Drawings>

310: modem unit 320: digital IF unit

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

350: power amplifier 410, 420, 430, 440: resonator

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

540: frequency generator 550: combiner

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 converting the I / Q signal received from the baseband into an IF signal; A multi-bit band pass delta sigma modulator for sampling the IF signal and outputting a multi-bit quantized IF signal; An RF up-modulator 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; Band pass delta sigma signal transmitter comprising a. The method of claim 1, And the multi-bit band pass delta sigma modulator samples the IF signal at a clock speed corresponding to four times the IF frequency. The method of claim 1, And the multi-bit band pass delta sigma modulator comprises a fourth-order resonator and a multi-bit quantizer. The method of claim 3, wherein the RF up-modulation unit, A plurality of AND gates for mixing the multi-bit quantized IF signal output from the multi-bit quantizer and the RF signal generated in the frequency generator; And A combiner for combining and outputting the mixed signal; Band pass delta sigma signal transmitter comprising a. The method of claim 1, wherein the power amplifier, A carrier power amplifier configured to amplify a carrier of the multi-bit quantized RF signal; A peak power amplifier configured to amplify the 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 generated during power combining of the power amplifier; Band pass delta sigma signal transmitter comprising a. The method of claim 1, And said power amplifier is a Doherty power amplifier. The method of claim 6, wherein the power amplifier, A phase error correction line that compensates the peak power amplifier for a 90 degree phase error generated by the quarter wave transformer; The band pass delta sigma signal transmitter further comprising.

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