KR20050057927A - Power amplifier for ofdm system terminal and method for biasing the same - Google Patents

Abstract

The present invention relates to a power amplifier for a terminal using an orthogonal frequency division multiplexing system (OFDM) and a biasing method thereof. In particular, the power amplifier for a terminal includes first and second driving stages, a power stage and a bias circuit. The first driving stage supplies driving power to the power stage, and the power stage amplifies and outputs the power supplied from the first driving stage. The second driving stage is inserted between the first driving stage and the power stage to drastically reduce the bias current of the power stage. The bias circuit applies bias to the first and second drive stages and the power stage. According to the present invention, by reducing the operating current of the power amplifier power stage for the terminal of the OFDM system, it is possible to reduce the unnecessary operating current of the OFDM terminal while satisfying the high PAPR of the OFDM system by using the power gain expansion characteristics of the power amplifier.

Description

Power amplifier for handset using orthogonal frequency division multiplexing system and biasing method {POWER AMPLIFIER FOR OFDM SYSTEM TERMINAL AND METHOD FOR BIASING THE SAME}

The present invention relates to a power amplifier and a biasing method for a terminal using an orthogonal frequency division multiplexing system, and more particularly, to an orthogonal frequency division multiplexing (OFDM) having a high peak to average power ratio (PAPR). The present invention relates to a structure of a power amplifier capable of reducing power consumption of a terminal without affecting system performance, and a biasing method thereof.

As a prior art, Korean Patent Application No. 1998-23776 (filed Jun. 23, 1998) discloses "an apparatus and method for controlling output power of a mobile communication terminal", wherein a power supply device controls a high frequency power amplifier and predetermined control. And a power supply device for varying the bias voltage and the bias current of the high frequency power amplifier, and a control unit for determining an output level according to the received signal strength and controlling the power supply devices according to the determined output level. Disclosed is an output power control apparatus and method which can reduce power consumption by effectively amplifying power by amplifying power by controlling bias / current of a power amplifier, which will be described in detail with reference to FIG. 1.

1 is a view showing a power amplifier structure that can increase the power efficiency of a mobile communication terminal using a controller according to the prior art.

Referring to FIG. 1, the controller 104 includes a separate memory to reduce DC power consumption of the power amplifiers 102 and 103. At this time, the memory stores the bias voltage values, the bias current control values, and the control values of the automatic gain amplifier, which are required to obtain a transmission signal having an optimum output level corresponding to the strength of the detected hand signal.

Received signal strength detection (RSSI) detection unit 105 detects the strength of the signal received from the base station to notify the control unit 104, the control unit 104 is notified from the received field strength detection unit 105 According to the received signal strength, the bias value, the bias current control value, and the automatic gain control value stored in the internal memory are read and supplied to each component.

The bias voltage control value and the bias current value are used as control values for adjusting the optimum bias voltage and bias current required by the power amplifiers 102 and 103. The automatic gain control value is a control value for controlling the power gain of the automatic gain amplifier 107 to obtain the power level required at the final output stage RF _out . In this case, the automatic gain control value should be determined in consideration of the power gains of the power amplifiers 102 and 103 which are changed by the bias voltage control value and the bias current control value.

On the other hand, when the control unit 104 intends to use the above-described control values in the form of a voltage value, the control unit 104 should be provided with an internal configuration or an additional configuration for generating a voltage value by the control of the control unit 104. The controller 104 may be included in a mobile station modem (MSM) or configured using a separate ASIC circuit. Here, reference numeral 101 denotes a variable power supply unit, 106 denotes a control signal line of the controller 104, 108 denotes a local oscillator, 109 denotes a mixer, and 110 denotes an amplifier.

However, the power amplifier structure of the control type as described above has the following problems.

First, the addition of additional components increases the cost of the terminal due to the nature of the terminal. This increases the area of the wafer, even if manufactured by ASIC, and requires additional cost.

Second, additional memory, control and variable supplies cause additional power consumption because they are active devices.

Third, the power amplifier structure described above has a backoff amount of about 3 dB due to the maximum power-to-average power ratio (PAPR) of the terminal in a cellular system such as IS-95 or CDMA, which can satisfy the effective maximum efficiency of the amplifier. However, in the case of a large amount of backoff such as OFDMA, the power gain compression point of the power amplifier for the terminal must be considerably high, and the operating current is large, so that the effective power part is difficult to expect an increase in efficiency when the above structure is applied. There is this.

Meanwhile, Korean Patent Application No. 2001-1032 (filed Jan. 8, 2001) discloses a "power control device for a mobile communication terminal", and the power control device for such a mobile communication terminal is a transmission signal input from the outside. A driving amplifier connected to the output of the driving amplifier, the first power amplifier suitable for a maximum power output for amplifying the signal for transmission to the outside through an antenna, and a transmission signal bypassed from the driving amplifier in the low power output mode A second power amplifier for amplifying with efficiency, switching means located at inputs and outputs of the drive amplifier to selectively switch inputs to the drive amplifier, and selective control of the switching means and control of activation or deactivation of the amplifier. It consists of control means, and it demonstrates concretely with reference to FIG.

FIG. 2 is a diagram illustrating a power amplifier structure capable of increasing power efficiency of a mobile communication terminal using a switch according to the prior art, and illustrates a method of switching amplifiers connected in parallel according to output power levels.

Referring to FIG. 2, first, the second power amplifier 202 is connected in parallel with the first power amplifier 203 so that the signal bypassed by the driving amplifier 201 at the time of input of the low power reception signal may be used to obtain the maximum efficiency for the power. It consists of an amplifier of the size that it can have. Here, the switches 204a and 204b are three-way switches, and two terminals are inserted into transmission lines at the front and rear ends of the driving amplifier 201 and selectively connected to a common terminal. Have.

In addition, the circuit of the mobile communication terminal receiver 206 transmits an external control signal to the control means 205 when the signal received from the base station falls below a predetermined level or voltage, and the control means 205 receives the drive amplifier 201. By activating the first switch 204a, 204b to transmit the transmission signal to the first power amplifier 203 through the drive amplifier 201.

However, the power amplifier structure of the control type using the switch as described above has the following problems.

First, power amplifiers connected in parallel have a problem of increasing price because additional amplifiers are required.

Second, because the structure requires a switch, the power consumption due to the switch can not be ignored, and there is a problem of additional price increase.

Third, in the case of a large amount of backoff such as OFDMA, the power gain compression point of the power amplifier for the terminal should be considerably high, and because the operating current is large, it is difficult to effectively increase the efficiency when the above structure is applied. There is a problem.

As described above, in the case of using the controller and the comparator in the module part of the power amplifier according to the prior art, or by inserting a switching element to bypass the transmission signal according to the size of the received signal (Bypass) or use a parallel amplifier In this case, it is impossible to realize the actual OFDM terminal due to the increased volume or additional cost. Also, because the OFDM system uses many subcarriers, the high PAPR results in a high maximum power output of the terminal. Since the average output power required and used is small, causing unnecessary power consumption of the terminal, a biasing structure is required to reduce the operating current of the OFDM terminal power amplifier and satisfy the linearity due to high PAPR.

An object of the present invention for solving the above problems is to provide a power amplifier and a biasing method for an OFDM terminal that can reduce the power consumption of the power amplifier in a terminal system having a large PAPR.

In addition, another object of the present invention is to design a power amplifier for an OFDM terminal, considering the volume and price, and to reduce the unnecessary operating current in the power amplifier when considering the high PAPR corresponding power addition efficiency (PAE: Power Added) An object of the present invention is to provide a power amplifier and a biasing method for an OFDM terminal which can increase battery life by increasing efficiency.

According to one aspect of the present invention for achieving the above object, a power amplifier for an OFDM system terminal,

A first driving stage supplying driving power; A power stage for amplifying and outputting power of the first driving stage; A second driving stage inserted between the first driving stage and the power stage to drastically reduce the bias current of the power stage; And a bias circuit for applying a bias to the first and second driving stages and the power stage.

Here, class AB biasing close to class A is preferably applied to the transistors of the power amplifiers used in the first and second driving stages.

In addition, the DC current consumption is reduced through the power gain expansion phenomenon due to the AB-class biasing close to the A class applied to the second driving stage.

In addition, the power stage is composed of a plurality of transistors connected in parallel, it is preferable to apply a class B biasing close to the class B.

In addition, after the power stage is biased to a section in which the power gain is constant with respect to the increase in the maximum output power level of the OFDM terminal, the power stage operates so that the output power requirement up to the peak power level is 1 kW power gain compression point. It is desirable to be.

A biasing method of a power amplifier for an OFDM terminal according to another aspect of the present invention,

a) biasing the first driving stage supplying the driving power to the class AB close to the class A; b) biasing the second driving stage inserted between the first driving stage and the power stage to the class AB close to the class A so as to rapidly reduce the bias current of the power stage which amplifies and outputs the power of the first driving stage; step; And c) biasing the power stage to an AB class close to the B class.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

Hereinafter, a power amplifier and a biasing method for an OFDM terminal according to an embodiment of the present invention will be described in detail.

Before describing a power amplifier structure and a biasing method according to an embodiment of the present invention, a conventional power amplifier will be briefly described.

The power amplifier handles a large signal instead of a small signal, where the small signal refers to a voltage whose amplitude of the signal voltage is much lower than the power supply voltage. On the other hand, a large signal has a value in which the amplitude of the signal voltage is almost close to the power supply voltage. Power amplifiers also handle high power, which means approximately 1 watt or more of power. The output stage of these power amplifiers requires linearity, and the degree of linearity is determined by total harmonic distortion (THD). Since the amount of power handled by the power amplifier is large, it is desirable to reduce the power consumed by the output transistor if possible. It is also possible to adopt small and light power supplies, so power consumption of the power amplifier should be kept as low as possible. Associated with this is power conversion efficiency. However, it does not achieve the maximum power conversion efficiency and the device's minimum power consumption at the same time.

The power amplifier is divided into class A amplifier, class B amplifier, class AB amplifier and class C amplifier by dividing the amplifier according to the position of its operating point. Here, the class A amplifier refers to an amplifier designed to position the operating point in the center of the active region so that a full period of 360 ° is output when a sinusoidal AC input signal is applied, and the class B amplifier is located at the boundary between the active region and the blocking region. The amplifier is designed so that the operating point is located and the signal is output only during the half period of 180 °. Class A amplifier refers to an amplifier having the intermediate characteristics of Class A and Class B amplifiers. Class C amplifiers indicate that the operating point is located in the cutoff region, and only a period of less than 180 ° appears as an output. In terms of power conversion efficiency, Class C is the highest, followed by Class B, Class AB, and Class A. The reason why the class A is the lowest is that the operating point current flows and power is consumed in the transistor element even when the input signal is not applied. Class B, on the other hand, consumes power from the transistor only when an input signal is applied.

3 is a diagram illustrating a power amplifier structure and a biasing method built in a terminal using an OFDM system according to an embodiment of the present invention.

Referring to FIG. 3, the structure of the power amplifier 300 according to the embodiment of the present invention includes two driving stages 301 and 302, a power stage 303, and a bias circuit 304. The transistor area of the power amplifier used for the driving stages 301 and 302 is small and performs a class AB biasing close to the A class, and serves to influence the gain of the entire power amplifier.

In the case of the power amplifier of the power stage 303 having the largest power consumption in the conventional power amplifier structure, the high output of the power amplifier is because the number of transistors connected in parallel is large and the operating current value used to obtain a constant gain is large. Power stage in the range is very large power consumption, shortening the terminal battery life.

In the embodiment of the present invention, the biasing method of the power stage 303 is characterized by reducing the power consumption for the operating current by biasing closer to the B class than the general AB class. .

In the biasing method of the power stage 303, when the amplifier is operated in the class AB close to the class B, the input power is increased as the negative portion of the output current signal is clipped, thereby increasing the DC current.

The increased DC current increases the trans-conductance (Gm) value among the transistor characteristics, and as the input power increases, the power gain increases. This phenomenon is called power gain extension, and as the operating current decreases, the amount of current to be clipped increases rapidly according to the input power.

In addition, when the current bias of the transistors used in the power stage 303 is low, the power gain is constant to some extent depending on the output power, and suddenly, the power gain expansion occurs. According to the embodiment of the present invention, OFDM is used by using the power gain extension. The amplifier is biased to the maximum output power level of the terminal system to a period where the power gain is constant, and then the amplifier is operated so that the output power requirement up to the peak power level is 1 kW power gain compression point.

In addition, in the case of bipolar transistors, reducing the operating current reduces the power gain at a small input power level compared to operating the normal operating current, but the compression gain is almost the same and the linearity does not change much. The reduction of the power gain due to the reduction of the operating current of 303 can be solved by adding one driving stage amplifier 302 to the driving stage 301 of the preceding stage.

Substantially the additional driving stage 302 is implemented as three to four transistors, so the additional cost and power consumption can be almost neglected. This extends the battery life of the terminal by reducing the operating current in a practically commercially available power amplifier structure and bias method of the OFDM terminal system.

4 is a diagram showing an output power and a power gain extension curve of a power amplifier according to an embodiment of the present invention, and an output power level and an highest output level according to PAPR of an OFDM terminal system.

Referring to FIG. 4, the power gain is flattened up to the average power level of OFDM, and the increase in power gain up to the peak power level required by the PAPR is caused by the power gain expansion phenomenon. Since the power gain expansion phenomenon is not a phenomenon due to the nonlinearity of the transistor but a phenomenon due to the increase of the DC current according to the bias condition, there is virtually no distortion due to the nonlinearity of the OFDM symbol having a very large peak power.

FIG. 5 is a diagram illustrating a comparison between input power and output power by a power amplifier biasing method and a general biasing method according to an embodiment of the present invention. A diagram showing input power versus output power of a power amplifier operated in a sudden manner.

As shown in FIG. 5, it can be seen that in FIG. 5, reducing the bias current of the power amplifier decreases only the power gain but hardly changes the maximum power point of the amplifier.

6 is a view showing a comparison between the power gain and the ACP according to the output power of the power amplifier biasing method and the general biasing method according to an embodiment of the present invention, when the power stage is operated in the AB class close to the B class It shows gain curve and ACP of power stage operated in normal AB class. Here, the ACP represents Adjacent Channel Power and is determined as the self channel power / male channel power.

As such, when operating the power stage in the class AB close to the class B, as shown by the reference B, the amount of operating current can be reduced to less than half, as shown by reference C in Figure 6, non-linear It can be seen that the distortion of the signal due to the noise is almost unchanged at about 2 to 3 kHz compared to the power amplifier operated in the AB class.

FIG. 7 is a diagram illustrating a comparison of PAE according to the output power of the power amplifier biasing method and the general biasing method according to an embodiment of the present invention. A diagram showing DC current consumption and PAE of a power amplifier operated in a sudden manner.

The PAE of this power amplifier is expressed as output power versus DC power consumption, which is closely related to the OFDM terminal battery consumption. As shown in FIG. 7, when the biasing according to the embodiment of the present invention is used rather than the general method, it can be seen that the PAE is increased compared with the case of operating in the AB class. Therefore, the operating current is very small in the range of the output power. Can be reduced by more than half.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto, and various other changes and modifications are possible.

According to the present invention, by providing a structure of a power amplifier that can be embedded in the OFDM terminal, it is possible to satisfy the high PAPR and extend the battery life of the terminal through the power gain expansion phenomenon according to the bias method of the driving stage and the power stage. .

1 is a view showing a power amplifier structure that can increase the power efficiency of a mobile communication terminal using a controller according to the prior art.

2 is a view showing a power amplifier structure that can increase the power efficiency of the mobile communication terminal using a switch according to the prior art.

3 is a diagram illustrating a power amplifier structure and a biasing method for a terminal using an OFDM system according to an embodiment of the present invention.

4 is a diagram illustrating an output power and a power gain extension curve of a power amplifier according to an embodiment of the present invention, and a maximum output level according to an output power level and a maximum power to average power ratio (PAPR) of an OFDM terminal system.

FIG. 5 is a diagram illustrating input power vs. output power by a power amplifier biasing method and a general biasing method according to an exemplary embodiment of the present invention.

FIG. 6 is a diagram illustrating a comparison between power gain and ACP according to output power of a power amplifier biasing method and a general biasing method according to an exemplary embodiment of the present invention.

FIG. 7 is a diagram illustrating the efficiency of power units according to output power by the power amplifier biasing method and the general biasing method according to an embodiment of the present invention.

Claims (8)

In a power amplifier for a terminal using an Orthogonal Frequency Division Multiplexing (OFDM) system, A first driving stage supplying driving power; A power stage for amplifying and outputting power of the first driving stage; A second driving stage inserted between the first driving stage and the power stage to drastically reduce the bias current of the power stage; And A bias circuit for applying a bias to the first and second driving stages and the power stage; Power amplifier for orthogonal frequency division multiplexing system terminal comprising a. The method of claim 1, A power amplifier for an orthogonal frequency division multiplexing system terminal, characterized by applying AB-class biasing close to class A for transistors of power amplifiers used in the first and second driving stages. The method of claim 2, Power amplifier for orthogonal frequency division multiplexing system terminal, characterized in that the DC current consumption is reduced through the power gain expansion due to the AB-class biasing close to the class A applied to the second drive stage. The method according to claim 1 or 2, The second driving stage is a power amplifier for a quadrature frequency division multiplexing system terminal, characterized in that consisting of three to four transistors. The method of claim 1, The power stage is composed of a plurality of transistors connected in parallel, power amplifier for orthogonal frequency division multiplexing system terminal, characterized in that the B-class biasing close to the B class is applied. The method according to claim 1 or 5, After biasing the power stage to a section where the power gain is constant with respect to the increase in the maximum output power level of the OFDM terminal, operating the power stage such that the output power requirement up to the peak power level is 1 kW power gain compression point. A power amplifier for orthogonal frequency division multiplexing system terminals. A method of biasing a power amplifier for a terminal using an orthogonal frequency division multiplexing (OFDM) system, a) biasing the first driving stage supplying the driving power to the class AB close to the class A; b) biasing the second driving stage inserted between the first driving stage and the power stage to the class AB close to the class A so as to rapidly reduce the bias current of the power stage which amplifies and outputs the power of the first driving stage; step; And c) biasing the power stage to the class AB close to the class B; A biasing method of a power amplifier for orthogonal frequency division multiplexing system terminal comprising a. The method of claim 7, wherein C), Biasing the power stage to a section in which a power gain is constant with respect to an increase in the maximum output power level of the OFDM terminal; And Operating the power stage such that the output power requirement up to the peak power level is 1 kW power gain compression point; A biasing method of a power amplifier for orthogonal frequency division multiplexing system terminal comprising a.