CN102299689B - High-efficiency double-frequency power amplifier design method based on envelop following technology - Google Patents

Abstract

The present invention provides a design method of a high-efficiency dual-frequency power amplifier based on the envelope tracking technology. The envelope tracking technology and the Doherty technology can be used simultaneously to further improve the efficiency of the power amplifier. Irrelevant, it can be applied to multi-frequency concurrent systems, and the envelope tracking technology can be used in combination with the digital pre-distortion technology to improve the linearity of the power amplifier while improving efficiency. In addition, the envelope tracking is relatively simple to implement, and the modules are independent. The same The structure can be applied to various power amplifier modules.

Description

Design Method of High Efficiency Dual-band Power Amplifier Based on Envelope Tracking Technology

technical field

The invention relates to the technical field of power amplifier design of wireless communication technology, in particular to a design method of a high-efficiency dual-frequency power amplifier based on envelope tracking technology.

Background technique

In contemporary wireless communication systems, the energy consumption of the system is an indicator of much concern. The radio frequency power amplifier is the core of the wireless base station, and its efficiency is the decisive factor affecting the efficiency of the base station. A variety of wireless communication technology standards and modulation modes make the signal have a higher power peak-to-average ratio (PAPR). For example, the peak-to-average ratio of the WCDMA single-carrier original signal is about 10.2dB, and that of TD-SCDMA is about 12dB, and OFDM will produce a larger peak-to-average ratio. In order to linearly amplify non-constant envelope modulation signals, power backoff is generally used to reduce the output distortion of class A or class AB power amplifiers to an allowable range. But for peak-to-average ratio signals, the power backoff severely degrades the power amplifier efficiency. That is, there is inevitably a trade-off between linearity and efficiency in power amplifier design. Therefore, pursuing high efficiency and maintaining linearity have become two hot spots in current power amplifier research.

Common technologies to improve power amplifier efficiency include switch mode (Class E) amplifier technology, Doherty technology, LINC technology, and envelope tracking technology (Envelope Tracking).

The drain efficiency of the power amplifier can be obtained by the following formula:

$\mathrm{<span\; class="notranslate">\; \&eta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}}$

In the formula, is the fundamental frequency output power; P ₀ =I ₀ V _dc is the DC power; I ₁ , V ₁ are the output fundamental wave voltage and current amplitudes respectively. I ₀ is a direct current, and V _dc is a direct current bias voltage. When the operating point range of the power amplifier is selected, the conduction angle is basically constant, is a constant. The efficiency η of the drain is only related to the ratio of V ₁ to V _dc . If the drain efficiency is to be improved, then this ratio must be as large as possible and kept as constant as possible. And the power added efficiency:

$\mathrm{<span\; class="notranslate">\; PAE</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&eta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; )</span>$

Therefore, the power added efficiency is directly proportional to the drain efficiency.

Envelope tracking technology is realized by using the principle that the efficiency of the amplifier is the best when it works in a saturated state. The basic idea is to determine the power supply voltage of the amplifier according to the envelope amplitude of the input RF signal: when the envelope is small, a low voltage power supply is used, and the voltage increases with the The envelope amplitude is increased and adjusted appropriately, so that the amplifier can work in the saturation region of the corresponding supply voltage under different power inputs, reducing power loss and achieving high efficiency.

Some working modes such as Class E and Class F power amplifiers can achieve very high drain efficiency, and ideally reach 100% drain efficiency, but the disadvantage of this type of power amplifier is that its linearity is relatively poor. The power amplifier of the Doherty structure has both higher efficiency (compared to class AB amplifier) and better linearity (compared to class C amplifier), and has been widely used in wireless communication base stations. However, due to its structural characteristics, the bandwidth is limited and cannot meet the requirements of broadband systems.

Therefore, a technical problem that needs to be solved urgently by those skilled in the art is: how to innovatively propose an effective measure to overcome the defects existing in the prior art and meet the requirements of practical applications.

Contents of the invention

The technical problem to be solved by the present invention is to provide a design method of a high-efficiency dual-frequency power amplifier based on envelope tracking technology. The designed power amplifier realizes the further improvement of the efficiency of the dual-frequency Doherty power amplifier through the envelope tracking technology, which can be realized in It is suitable for the power amplifier in the final radio frequency output of the mobile communication base station, has high efficiency, and can realize dual-frequency concurrent work at the same time.

In order to solve the above problems, the present invention discloses a method for designing a high-efficiency dual-frequency power amplifier based on envelope tracking technology, including:

The original digital signal is divided into two outputs, one is the envelope signal, the other is the delayed original signal, and the two outputs are respectively converted into analog signals by digital-to-analog conversion;

The envelope signal provides a bias voltage for the drain of the Doherty power amplifier through a linear voltage amplifier;

The high-voltage side current detection amplifier detects the output current of the linear voltage amplifier, and controls the voltage-controlled current source through the output voltage, and uses the current source to provide current for the drain bias terminal of the Doherty power amplifier;

The output signal of the envelope amplifier is input to the DC bias terminal of the dual-frequency concurrent Doherty power amplifier, and the delayed original signal is input to the input terminal of the Doherty power amplifier to be amplified by the Doherty power amplifier;

The output signal of the Doherty power amplifier is coupled back to the DSP, and the sampled signal is compared with the original signal to determine the delay length;

Wherein, the envelope amplifier includes a linear part, a nonlinear part, a detection resistor and a hysteresis comparator. The linear part includes an operational amplifier and a class AB push-pull output stage, and the nonlinear part includes a PMOS switch tube, a diode and an inductor.

Preferably, the input and output sequences are correlated, and the delay value with the largest correlation coefficient is used for delay.

Preferably, the typical value of the delay is 10 ns.

Preferably, when amplified by a Doherty power amplifier, its gain depends on the transistors used.

Preferably, when the type of the transistor is Cree24010, the output power at the 1dB compression point can reach 42dBm under the operating voltage of 48V.

Compared with the prior art, the present invention has the following advantages:

The present invention provides a design method of a high-efficiency dual-frequency power amplifier based on the envelope tracking technology. The envelope tracking technology and the Doherty technology can be used simultaneously to further improve the efficiency of the power amplifier. Irrelevant, it can be applied to multi-frequency concurrent systems, and the envelope tracking technology can be used in combination with the digital pre-distortion technology to improve the linearity of the power amplifier while improving efficiency. In addition, the envelope tracking is relatively simple to implement, and the modules are independent. The same The structure can be applied to various power amplifier modules.

Description of drawings

Fig. 1 is a schematic diagram of a design method of a high-efficiency dual-frequency power amplifier based on envelope tracking technology described in a specific embodiment of the present invention;

Fig. 2 is the high-efficiency dual-band Doherty power amplifier structure schematic diagram based on envelope tracking technology described in the specific embodiment of the present invention;

Fig. 3 is a schematic structural diagram of the functional module of the envelope amplifier described in the specific embodiment of the present invention;

Fig. 4 is the envelope amplifier circuit block diagram described in the specific embodiment of the present invention;

Fig. 5 is the envelope amplifier efficiency and load resistance relation diagram described in the specific embodiment of the present invention;

Fig. 6 is the output signal of the high-efficiency dual-frequency/multi-frequency Doherty power amplifier based on the envelope tracking technology described in the specific embodiment of the present invention in the frequency domain with the original signal and the signal comparison figure after direct amplification; Wherein, Fig. 6a is a signal with a carrier frequency of 960MHz, and Figure 6b is a signal with a carrier frequency of 2GHz.

Detailed ways

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

The basic principle of the Doherty circuit is to separately amplify the average part and the peak part of the input signal, and then synthesize them to obtain high efficiency. Due to the active load-pulling characteristics of the Doherty structure, the power amplifier can guarantee higher efficiency within a certain power back-off range, and meet the amplification requirements of modulation signals with different peak-to-average ratios. The combination of envelope tracking technology and Doherty power amplifier can realize high efficiency and high linearity power amplifier. It is suitable for power amplifiers in the final RF output of mobile communication base stations, and its output power and signal bandwidth have higher indicators than traditional envelope tracking amplifiers. This puts forward higher requirements on the output voltage and speed of the envelope amplifier that amplifies the envelope signal. While meeting these requirements, it is also necessary to ensure that the envelope amplifier has a high efficiency, so as to ensure the efficiency of the overall power amplifier. In addition, since the envelope signal and the original signal are simultaneously input to the DC terminal and the signal terminal of the power amplifier in order to realize envelope tracking, time alignment of the two signals needs to be completed.

With reference to Fig. 1, show a kind of design method schematic diagram of the high-efficiency dual-frequency power amplifier based on envelope tracking technology of the present invention, described method specifically comprises:

In step S101, the original digital signal is divided into two outputs, one is an envelope signal, and the other is a delayed original signal, and the two outputs are respectively converted into analog signals through digital-to-analog conversion;

Step S102, the envelope signal provides a bias voltage for the drain of the power amplifier through the linear voltage amplifier;

Step S103, the high-voltage side current detection amplifier detects the output current of the linear voltage amplifier, and controls the voltage-controlled current source through the output voltage, and uses the current source to provide current for the drain bias terminal of the power amplifier;

Step S104, inputting the output signal of the envelope amplifier into the DC bias terminal of the dual-frequency concurrent Doherty power amplifier, and simultaneously inputting the delayed original signal into the input terminal of the power amplifier for amplification by the power amplifier;

In step S105, the output signal of the power amplifier is coupled back to the DSP, and the sampled signal is compared with the original signal to determine the delay length.

Among them, the input and output sequences are correlated, and the delay value with the largest correlation coefficient is taken for delay. The typical value of delay is 10ns.

When a power amplifier is amplified, its gain depends on the transistors used.

When using the transistor model as Cree24010, the output power of the 1dB compression point can reach 42dBm under the operating voltage of 48V.

Referring to Figure 2, first of all, it is necessary to determine the high-efficiency dual-band Doherty power amplifier structure based on envelope tracking technology. The invention proposes a high-efficiency power amplifier structure based on envelope tracking technology. It is generally divided into four parts: DSP digital processing, envelope amplifier, dual-frequency/multi-frequency concurrent Doherty power amplifier and voltage coupling feedback loop.

The DSP digital processing module processes the I/Q data of the digital domain signal and outputs the envelope At the same time, the I/Q data is delayed by Δt, where Δt can be obtained through prior training, and the baseband I/Q signal of the power amplifier is complexly correlated to synchronize the input and output data, and the delay with the highest correlation is Δt. At the same time, appropriate pre-distortion processing can be performed on the I/Q data for a specific power amplifier.

Then, determine the envelope amplifier structure. The envelope amplifier of the present invention adopts the structure of a linear-assisted switch-mode voltage converter, which is composed of a wide-band linear part (but low efficiency) and a narrow-band switching part (high efficiency), as shown in FIG. 3 . The linear part and the switch part are connected by the detection resistor R _sense , and the current and voltage of each part have the following relationship:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; linear</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; Rload</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; sw</span>}}\\ {\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; Rload</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; load</span>}}\end{array}\right.$

If i _Rload →0, then i _sw →V _s /R _load , which means that the voltage on the load is synchronized with the voltage source, and the current source provides almost all the power.

Such a structure is intended to achieve power separation between the linear part and the switching part, while taking into account high efficiency and broadband. For WiMAX baseband signals, 99% of the envelope signal energy is concentrated below 8MHz, so the bandwidth of the envelope amplifier needs to reach at least 80MHz to meet the linearity requirements of the power amplifier.

Referring to Figure 4, a general block diagram of the envelope amplifier is shown.

The linear part is amplified by an operational amplifier and a class AB push-pull output stage. The common-mode output voltage of the push-pull output stage needs to be adjusted according to the PAPR of the input signal and the peak DC bias voltage of the power amplifier. The voltage stability of the linear part is strong, which can provide a stable envelope amplification voltage, which is equivalent to a voltage source;

The linear part can amplify the voltage, but due to the limited output current of the op amp and the push-pull output stage used, and the low efficiency, it is difficult to provide enough power for the drain of the power amplifier. The nonlinear part has high efficiency and mainly provides power to the drain of the power amplifier. It is composed of a PMOS switch tube, a diode and an inductor. A resistor R _sense for detecting the direction of the current and a hysteresis comparator detect the magnitude of the output current of the linear part to control the switch. When the output current of the linear part is large, the comparator outputs a low level, and the PMOS transistor switch is turned on. At this time, the cathode voltage of the diode is V _DD , the diode is turned off, and the switch supplies power to the drain bias; when the output current of the linear part is small or In the reverse direction, the comparator outputs a high level, and the PMOS tube switch is turned off. Due to the existence of the inductance, it is necessary to keep the current from jumping. At this time, the diode is turned on and supplies power to the drain bias. That is, when i _linear *R _sense <h, V _D =0; when i _linear *R _sense >h, V _D =V _SS ; in other cases, V _D remains unchanged.

Adjust the parameters to complete the envelope amplifier, and realize the efficiency as shown in Figure 5, which can reach 71%.

Design a DSP-based digital pre-distortion algorithm to reduce the nonlinearity of the power amplifier and improve the gain reduction caused by envelope tracking. Synchronizing the envelope signal is performed by performing complex correlation on the baseband signal of the power amplifier.

Referring to Figures 6a-6b, it shows that two different WiMAX signals are used as baseband signals, respectively modulated with carrier frequencies of 960MHz and 2000MHz. The comparison between the output signal and the original signal, the blue curve is the input original signal spectrum, the red curve is the signal spectrum directly amplified by the power amplifier module, and the black curve is the signal spectrum amplified by the power amplifier using envelope tracking technology. It can be seen that while the efficiency is improved, the deterioration of the linearity is small, within an acceptable range.

The high-efficiency dual-frequency/multi-frequency Doherty power amplifier based on the envelope tracking technology of the present invention uses the envelope tracking technology as the design basis for improving the efficiency of the dual-frequency/multi-frequency Doherty power amplifier. The envelope tracking technology amplifies the envelope of the input signal as a drain bias, which can realize the power tube to work in a saturated state under low input power, thereby improving the drain efficiency. The high-efficiency dual-frequency/multi-frequency Doherty power amplifier based on the envelope tracking technology of the present invention has a clear structure, is simple to realize, can effectively improve the additional efficiency of the drain electrode, and does not affect the linearity.

Above, the design method of a high-efficiency dual-frequency power amplifier based on envelope tracking technology provided by the present invention has been introduced in detail. In this paper, specific examples have been used to illustrate the principle and implementation of the present invention. The above embodiments The description is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation and scope of application. In summary, As stated above, the content of this specification should not be construed as limiting the present invention.

Claims (4)

1. a design method based on the high-efficiency dual-band power amplifier of envelope tracking technology, it is characterized in that, comprising: The original digital signal is divided into two outputs, one is the envelope signal, the other is the delayed original signal, and the two outputs are respectively converted into analog signals by digital-to-analog conversion; The envelope signal provides a bias voltage for the drain of the Doherty power amplifier through a linear voltage amplifier; The high-voltage side current detection amplifier detects the output current of the linear voltage amplifier, and controls the voltage-controlled current source through the output voltage, and uses the current source to provide current for the drain bias terminal of the Doherty power amplifier; The output signal of the linear voltage amplifier is input to the DC bias terminal of the dual-frequency concurrent Doherty power amplifier, and the delayed original signal is input to the input terminal of the Doherty power amplifier, which is amplified by the Doherty power amplifier; The output signal of the Doherty power amplifier is coupled back to the DSP, and the sampled signal is compared with the original signal to determine the delay length; Wherein, the linear voltage amplifier includes a linear part, a nonlinear part, a detection resistor and a hysteresis comparator, the linear part includes an operational amplifier and a class AB push-pull output stage, and the nonlinear part includes a PMOS switch tube, a diode and an inductor. 2. The method of claim 1, wherein: Correlate the input and output sequences, and take the delay value with the largest correlation coefficient for delay. 3. The method of claim 1, wherein: When amplified by a Doherty amplifier, the gain depends on the transistors used. 4. The method of claim 3, wherein: When using the transistor model as Cree24010, the output power of the 1dB compression point can reach 42dBm under the operating voltage of 48V.