JP2008066867A - Power amplifier control unit, and mobile communication terminal unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly control the supply voltage of a power amplifier to load variation, while removing an isolator. <P>SOLUTION: A transmission power detector 127 detects transmission power, and a reflection power detector 128 detects reflection power from an antenna 115. A phase detector 120 detects the phase of the reflection power. A DCDC controller 109 controls a DCDC converter 103 based on the outputs of the transmission power detector 127, the reflection power detector 128 and the phase detector 120, and variably controls a supply voltage VDD to be supplied to a power amplifier 111. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mobile communication terminal device, and more particularly to a power amplifier control device thereof.

  The demand for cost reduction and size reduction required for terminal RF circuits due to the thinning and miniaturization of the terminal shape due to the multi-functionalization and design refinement of recent mobile phone terminal devices (hereinafter simply referred to as terminals). Has become very large.

  It is said that the isolator connected to the power amplifier output of the transmission block has been reduced in mechanical size to the limit, and further miniaturization cannot be expected. Therefore, it can be said that it is desirable to remove the isolator if possible from the viewpoint of miniaturization and cost reduction. The isolator is an important component that absorbs the reflected power from the antenna due to fluctuations in the antenna impedance so that the load of the power amplifier always looks 50 ohms. Therefore, if the isolator is removed, the output signal of the power amplifier may be distorted, or desired characteristics may not be obtained. It is necessary to carefully consider the influence.

  FIG. 2 shows a transmission block configuration of a general CDMA (Code Division Multiple Access) mobile phone terminal. This transmission block includes a battery 201, a DCDC converter 203, a coil 204, a capacitor 205, a baseband processing unit 206, an RF modulator and variable gain unit 208, a power amplifier 211, a directional coupler 213, an isolator 214, an antenna 215, a transmission A power detection unit 227 is included.

  In the transmission block, a certain level of transmission output is determined by a command from the base station. Since the power amplifier 211 is adjusted so as to be most efficient at the maximum power, it is used so that the DCDC converter 203 applies a low power supply voltage VDD and operates efficiently when the output is low. FIG. 3 shows how VDD is generated by the DCDC converter 203 in accordance with the output power. In the case of a low terminal output, a low VDD is supplied, and in the case of a high output, a high VDD is supplied. A data table corresponding to this figure is held in the baseband processing unit 206. The baseband processing unit 206 controls the DCDC converter 203 with the control signal VCNTL according to the output level. A normal DCDC converter IC is configured to output a voltage proportional to the control signal VCNTL. In a general CDMA terminal, VDD_MIN = 1.0V in FIG. 3 and VDD_MAX = 3.5V.

  The I and Q signals to be transmitted and the transmission power level Pow are sent from the baseband processing unit 206 to the RF modulator and variable gain unit 208. A desired RF signal is output from the output of the RF modulator and variable gain device 208 and input to the power amplifier 211. After being amplified to a desired output level by the power amplifier 211, the output signal is input to the antenna 215 and transmitted. Further, in order to detect whether or not the actual output level is correctly transmitted to a desired level, the transmission signal is partially coupled using the directional coupler 213 and input to the transmission power detection unit 227. The detection voltage VDET_F output from the detection unit is fed back to the baseband processing unit 206 and used to finely adjust the transmission power level Pow.

  Also, if the user holds the antenna or terminal, or places the terminal on a metal desk or the like, the antenna input impedance will deviate from 50 ohms, and power will be reflected from the antenna to the amplifier. The isolator 214 has a function of absorbing the reflected power, and the load of the power amplifier 211 always looks 50 ohms.

  The operation of the amplifier when the load impedance fluctuates will be described with reference to FIG. FIG. 4 shows how the distortion (Adjacent Channel Power leakage Ratio: ACPR) and current consumption (IDD) of the power amplifier output a predetermined maximum output when the load impedance fluctuates. The change is indicated by contour lines on the Smith chart. Contour lines indicated by alternate long and short dash lines indicate ACPR [dBc], and contour lines indicated by broken lines indicate IDD [mA].

  The power supply voltage VDD = 2.5V, and the signal is based on HPSK modulation used in the IS-2000 system. In the IS-2000 system, ACPR specifications (specifications) are defined, and the ACPR of the terminal output signal is required to be a value lower than -42 dBc. When the terminal is in an ideal free space state, the load is generally 50Ω at the center of the Smith chart (center triangle in the figure). At that time, ACPR = −48 dBc, IDD = 500 mA. Now, for example, if the load fluctuates in the direction of arrow A, it degrades to near ACPR = −42 dBc, IDD = 600 mA, and the operation is just a spec.

  Conventionally, various attempts have been made to remove the isolator. However, as can be seen in Non-Patent Document 1, most methods rely on the good linearity of the device to forcibly remove the isolator. In general, when designing a power amplifier, there is a trade-off between linearity and power consumption. Therefore, the efficiency of the power amplifier is always sacrificed when this method is used. Also, even if the antenna impedance deviates significantly from 50Ω, unnecessary radiation power such as ACPR must always meet the specifications, so an adjustment circuit must be inserted between the power amplifier and the antenna to meet the specifications. Must not. The design of this adjustment circuit is very time-consuming, and the development cost of the mobile phone terminal increases accordingly.

  On the other hand, there is a method in which a variable matching circuit and a load detection circuit are inserted between the power amplifier and the antenna, the load fluctuation is detected, and the load of the power amplifier is controlled to 50 ohms. Although this method has good load fluctuation suppression characteristics, there is a problem that the loss of the variable matching circuit inevitably increases. In order to offset this loss, the output of the power amplifier must be further increased, resulting in an increase in power consumption. Another problem is that it is very difficult to implement a variable matching circuit.

  In Non-Patent Document 2, a variable matching circuit using a variable capacitance and an inductor is used. In order to realize the variable capacitance, a method in which capacitors and semiconductor switches connected in cascade are arranged in parallel along the main path. In this case, a semiconductor switch is inserted in parallel to the output RF path of the power amplifier. I have to prepare. In Non-Patent Document 2, this is realized by using a very expensive technology called Silicon-on-Sapphire, which is unrealistic in terms of cost when applied to an actual terminal. In addition, a method using MEMS and a method using a varactor have been proposed, but none of them is satisfactory in terms of cost and performance.

The method of Patent Document 1 employs a method of improving the distortion characteristics of the power amplifier by detecting the antenna reflected power caused by the antenna load fluctuation by the directional coupler and increasing the power supply voltage by the DCDC converter. Generally, when the power supply voltage of the power amplifier is made higher than the level assumed at the time of design, the load map of IDD does not substantially change, but the load map of ACPR has a feature that a region with low distortion spreads (see Patent Document 1). . Therefore, in Patent Document 1, when the detected reflected power becomes large, the power supply voltage VDD of the power amplifier is boosted and a high voltage is applied to control deterioration of distortion.
JP 2003-338714 A Tetsuo Sato, Chris Grigorean, “Design Advantages of CDMA Power Amplifier Built with MOSFET Technology”, Microwave Journal, Oct. 2002 Dongjiang Qiao, David Choi, Yu Zhao, Dylan Kelly, Tsaipi Hung, Donald Kimball, Mingyuan Li, and Peter Asbeck, "Antenna Impedance Mismatch Measurement and Correction for Adaptive CDMA Transceivers", 2005 IEEE MTT-S International Microwave Symposium Digest

  Although the isolator can be removed according to the method described in Patent Document 1, there are the following problems.

  That is, according to the load map of the power amplifier, there is a region where the distortion characteristics are sufficiently satisfied without increasing the power supply voltage. For example, such a region corresponds to the region of arrows B and C in FIG. However, in the technique described in Patent Document 1, only the magnitude (amplitude) of the reflected power is detected. Therefore, when the reflected power is present, the voltage is always boosted to a high voltage, resulting in unnecessary power consumption. Become. In Patent Document 1, consideration is given to using a supply current monitor circuit (current detection resistor) so as not to increase the voltage in a load region where the current is high. Consumption will occur.

  Further, as shown in region C of FIG. 4, even if the reflection is large and the current is not large, there are not a few regions where the distortion satisfies the specifications and the power supply voltage does not need to be boosted. Then, as much as boosting, wasteful power consumption occurs.

  Furthermore, even in the load region where the reflection is large and the current is large as in the region A of FIG. 4, there is a portion where the distortion has deteriorated to the limit of the spec out, and the power source is said to be unnecessarily high. In other words, there is a problem of malfunction, that is, distortion increases when the voltage is lowered.

  The present invention has been made in such a background, and intends to more appropriately control the power supply voltage of the power amplifier with respect to load fluctuations while removing the isolator.

  A power amplifier control apparatus according to the present invention includes a power amplifier that amplifies a transmission signal supplied to an antenna, voltage varying means that changes a battery voltage and supplies the power amplifier as a power supply voltage, and amplitude and phase of reflected power from the antenna. And a control means for controlling the voltage varying means according to at least the detected amplitude and phase.

  The control means can more appropriately control the power supply voltage of the power amplifier with respect to load fluctuations by considering not only the amplitude but also the phase of the reflected power from the antenna.

  The control means has a data table storing at least the amplitude and phase of the reflected power and the control value of the power supply voltage of the power amplifier associated with the reflected power, and the detected amplitude and phase The data table is referred to, and a control value corresponding to the detected amplitude and phase is output to the voltage varying means.

  A mobile communication terminal apparatus according to the present invention is a mobile communication terminal apparatus including a transmission block, and includes the transmission block having the above-described configuration.

  According to the present invention, by removing an expensive isolator having a large size, it is possible to contribute to a reduction in terminal manufacturing cost and a reduction in terminal size. In addition, even if the reflected power cannot be absorbed by removing the isolator, the power amplifier power supply voltage is controlled in consideration of not only the amplitude but also the phase of the reflected power. It became possible to solve the problem of power consumption.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a transmission block of the mobile phone terminal device according to the present embodiment. This configuration avoids characteristic deterioration due to fluctuations in the antenna load of the power amplifier.

  This transmission block includes a DC power supply (battery) 101, a DCDC converter 103, a coil 104, a capacitor 105, a baseband processing unit 106, an RF modulator and variable gain unit 108, a DCDC control unit 109, a power amplifier 111, and a directional coupler. 113, an antenna 115, low-pass filters 121 and 122, multipliers 123 and 124, a π / 2 phase shifter 125, a transmission power detection unit 127, and a reflected power detection unit 128. In this embodiment, the DCDC converter 103 is dedicated for step-down. The elements 121 to 125 constitute a phase detector 120 that detects the phase of the reflected signal Pr.

  Compared with the general power amplifier shown in FIG. 2, the power amplifier 111 is adjusted so as to obtain a desired output characteristic even with a low power supply voltage. A general power amplifier is adjusted to obtain a desired characteristic at VDD = 3.5V, but the power amplifier 111 of FIG. 1 is adjusted to operate at a lower voltage, for example, VDD = 2.5V. Keep it. That is, adjustment is made so that VDD_MAX in FIG. 3 is 2.5V. In general, when a power amplifier adjusted at VDD = 2.5V is operated at a high power supply voltage, for example, VDD = 3.5V, linearity is enhanced and characteristics such as distortion and gain are robust against load fluctuations. become. Instead, as the power supply voltage increases, power consumption increases and power efficiency deteriorates. However, unlike Patent Document 1, since the boost converter is not used, the efficiency is higher.

  The main operations related to the present invention of the transmission block of FIG. 1 will be described below. A method of generating a desired output is the same as that of the transmission block shown in FIG.

  A part of the transmission signal (forward output signal) Pf of the directional coupler 113 is input to the transmission power detection unit 127, and a detection output VDET_F is obtained. A part of the reflected signal (reverse direction output signal) Pr of the directional coupler 113 is input to the reflected power detector 128, and a detection output VDET_R is obtained.

  The transmission signal (forward output signal) Pf is further branched, one being input to the multiplier 123 as it is, and the other being input to the multiplier 124 via the π / 2 phase shifter 125. The reflected signal (reverse direction output signal) Pr is also branched and input to the multipliers 123 and 124 as they are.

The phase component signals P_gamma_I and P_gamma_Q output from the multipliers 123 and 124 are expressed as follows. Now, assuming that Pf = A · cos (2πf · t) and antenna impedance (reflection coefficient) Γ = | Γ│ · exp (j · φ),
Pr = A ・ │Γ│ ・ cos (2πf ・ t + φ)
It becomes. At this time, the multiplier output P_gamma_I is
P_gamma_I ＝ A ・ cos (2πf ・ t) ・ A ・ │Γ│ ・ cos (2πf ・ t + φ)
＝ A ²・ │Γ│ ・ 0.5 ・ [cos (2 ・ 2πf ・ t) + cos (-φ)]
P_gamma_Q = A ・ sin (2πf ・ t) ・ A ・ │Γ│ ・ cos (2πf ・ t + φ)
＝ A ²・ │Γ│ ・ 0.5 ・ [cos (2 ・ 2πf ・ t) + sin (φ)]
It becomes. Here, f represents the carrier frequency, and the conversion gain of the multiplier is assumed to be 1.

The first term in the parenthesis in the above equation is blocked by the low-pass filters 121 and 122, and the phase component signal P_gamma_BB_I, Q is as the following equation consisting of the second term.
P_gamma_BB_I ＝ k ・ │Γ│ ・ cos (φ)
P_gamma_BB_Q ＝ k ・ │Γ│ ・ sin (φ)

  If it is desired to obtain | Γ | more accurately, | Γ | may be obtained from the relationship | Γ | ∝VDET_R.

  As described above, the antenna reflection coefficient Γ can be accurately obtained from the three pieces of information of | Γ |, cos (φ), and sin (φ).

  When this configuration is adopted, it is necessary to use a multiplier or a mixer, but a simple one with inferior performance compared to that mounted on an RF modulator or the like is sufficient, and it is integrated into a modulator IC or the like ( If integrated), the size will not be so large.

The DCDC control unit 109 calculates Γ based on | Γ |, cos (φ), and sin (φ). As is well known, the relationship between Γ and φ includes Γ = α + jβ, φ = arctan (β / α), and | Γ | = √ (α ² + β ² ) <1. Based on the obtained Γ and the load map of the power amplifier as shown in FIG. 4 measured in advance, the output voltage of the DCDC converter is finely controlled. For example, when the output is the maximum output and the antenna impedance is fluctuating in the direction of B, since there is a margin for distortion, the power supply voltage VDD is controlled to be maintained at 2.5V. Further, when the load fluctuates in the direction A, since the distortion is greatly deteriorated, the power supply voltage is controlled to be increased to a level at which the distortion satisfies the specifications. Such control is realized, for example, by providing a data table in which input parameters and output parameters are stored in association with each other and referring to the data table as necessary.

  FIG. 5 schematically shows a configuration example of such a data table 500. In this example, the magnitude of transmission power (VDET_F), phase φ (P_gamma_BB_I, P_gamma_BB_Q), and the magnitude of reflected power (VDET_R), which are input parameters, are stored in association with the control value VCNTL, which is an output parameter. Yes.

  According to the present embodiment, by detecting not only the magnitude of the reflected power but also its phase, the power supply voltage of the power amplifier can be adjusted more appropriately. Further, by using not a step-up / step-down switching power supply circuit but a step-down converter circuit as the voltage varying means, the circuit scale can be reduced and the efficiency can be improved.

  FIG. 6 shows a configuration example of a transmission block according to the second embodiment of the present invention. Elements that are the same as those shown in FIG. 1 are given the same reference numerals, and redundant descriptions are omitted.

  The transmission block in FIG. 6 differs from the transmission block in FIG. 1 in that the DCDC control unit 109 in FIG. 1 outputs a multilevel control signal, whereas the DCDC control unit 109a in FIG. Is output. Further, a switching element (SW) 600 (for example, FET) whose conduction is controlled in accordance with the binary control signal is provided. Switching element 600 selectively applies battery voltage VBAT directly to power amplifier 111 in accordance with a binary control signal from DCDC control unit 109a. Specifically, when the antenna reflection is small, the DCDC control unit 109a always turns off the switching element 600 and sets the output of the DCDC converter 103 to VDD. The VDD at this time is V1 or V2 depending on the magnitude of the output power Pout. When the antenna reflection is large, the switching element 600 is turned OFF and the output of the DCDC converter 103 is set to VDD when the output power Pout is smaller than a predetermined magnitude PowerX, but switching is performed when the output power Pout is equal to or greater than the predetermined magnitude PowerX. The element 600 is turned ON and the battery voltage VBAT is set to VDD. At this time, the DCDC converter 103 is turned off (non-operating state). In order to use the data table 500 shown in FIG. 5 for such an operation, the value of VCNTL is made binary (“0” or “1”), and the switching element 600 and the DCDC converter 103 are Binary switching data for complementary ON / OFF control is added.

  FIG. 7 shows how the power supply voltage VDD of the power amplifier 111 in FIG. 6 is controlled. As can be seen from this figure, when the reflected power of the antenna is smaller than the predetermined value, as shown in FIG. 7A, when the output power Pout is less than the predetermined value PowerX, the DCDC converter 103 becomes the output voltage V1. . Therefore, the power supply voltage VDD is maintained at V1. When the output power Pout is equal to or greater than the predetermined value PowerX, the DCDC converter 103 becomes the output voltage V2. Therefore, the power supply voltage VDD is maintained at V2. When the reflected power of the antenna is greater than or equal to a predetermined value, as shown in FIG. 7B, when the output power Pout is less than the predetermined value PowerX, the DCDC converter 103 becomes the output voltage V1, but the output power Pout is predetermined. Above the value PowerX, the battery voltage VBAT is directly at VDD. As can be seen from the graph of FIG. 3, the preferable VDD curve rises gently until the output power reaches a predetermined value, and then rapidly increases after exceeding the predetermined value. Therefore, even if the power supply voltage is controlled in a binary manner as shown in FIG. 7, the efficiency does not decrease so much, and the control can be simplified. In addition, since the DCDC converter 103 is in a non-operating state at the time of high reflection and high output power, the operating power becomes zero.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made. For example, the magnitude of the reflected power is detected by the reflected power detector 128, but it can also be obtained by calculation based on the output of the phase detector 120.

It is a figure which shows the structure of the transmission block of the mobile telephone terminal device in embodiment of this invention. It is a figure which shows the transmission block structure of a general CDMA mobile telephone terminal. It is a graph which shows the mode of VDD production | generation according to output electric power by the DCDC converter shown in FIG. Smith chart showing how the power amplifier distortion (ACPR) and current consumption (IDD) change when the load impedance changes and the power amplifier outputs a predetermined maximum output. It is. It is a figure which shows typically the structural example of the data table used by embodiment of this invention. It is a figure which shows the structural example of the transmission block which concerns on the 2nd Embodiment of this invention. It is a graph which shows the mode of control of power supply voltage VDD of the power amplifier shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 103 ... Converter, 104 ... Coil, 105 ... Capacitor, 106 ... Baseband processing part, 108 ... Variable gain device, 109 ... Control part, 109a ... Control part, 111 ... Power amplifier, 113 ... Directional coupler, 115 ... Antenna , 120 ... phase detector, 121, 122 ... low pass filter, 123, 124 ... multiplier, 125 ... phase shifter, 127 ... transmission power detector, 128 ... reflected power detector, 201 ... battery, 203 ... DCDC converter, 204 ... Coil, 205 ... Capacitor, 206 ... Baseband processing unit, 208 ... Variable gain unit, 211 ... Power amplifier, 213 ... Directional coupler, 214 ... Isolator, 215 ... Antenna, 227 ... Transmission power detection unit, 500 ... Data table, 600 ... switching element

Claims (7)

A power amplifier for amplifying a transmission signal supplied to the antenna;
Voltage varying means for changing the battery voltage and supplying the power amplifier as a power supply voltage;
Detection means for detecting the amplitude and phase of the reflected power from the antenna;
And a control means for controlling the voltage varying means according to at least the detected amplitude and phase.   The control means has a data table storing at least the amplitude and phase of the reflected power and the control value of the power supply voltage of the power amplifier associated with the reflected power, and the detected amplitude and phase 2. The power amplifier control device according to claim 1, wherein the data table is referred to, and a control value corresponding to the detected amplitude and phase is output to the voltage varying means.   The power amplifier is adjusted so that a desired output characteristic can be obtained with a predetermined power supply voltage relatively low with respect to the battery voltage, and the voltage varying means steps down the battery voltage to be equal to or lower than the predetermined power supply voltage. The power amplifier control device according to claim 1, further comprising a DCDC converter.   The power amplifier control device according to claim 1, wherein the control means performs multi-value control on the voltage variable means.   The control means performs binary control of the voltage variable means, and the voltage variable means is a DCDC converter that controls ON / OFF according to a binary output of the control means to step down the battery voltage to the predetermined voltage, and the reflection The power amplifier control device according to claim 1, further comprising: a switch that directly applies a battery voltage to the power amplifier when the power is equal to or greater than a predetermined value.   The detection means for detecting the phase includes a first multiplier that multiplies the reflected signal from the antenna and the transmission signal to the antenna, a phase shifter that shifts the transmission signal to the antenna by 2 / π, and the phase shifter. A second multiplier for multiplying the output of the phase shifter by the reflected signal from the antenna, and first and second low-pass filters for low-pass filtering the outputs of the first and second multipliers, respectively. Item 4. The power amplifier control device according to Item 1. In a mobile communication terminal device provided with a transmission block,
The transmission block is:
A power amplifier for amplifying a transmission signal supplied to the antenna;
Voltage varying means for changing the battery voltage and supplying the power amplifier as a power supply voltage;
Detection means for detecting the amplitude and phase of the reflected power from the antenna;
And a control means for controlling the voltage varying means according to at least the detected amplitude and phase.

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