KR20050029998A - Power combining method for power combining structure having arbitrary electric length for doherty amplifier - Google Patents

Abstract

A power connection method for the power combining structure of Doherty amplifier with an arbitrary electric length is provided to realize the miniaturization of Doherty amplifier by improving the physical length of the lambda/4 transmission line of power connection unit. A power connection method for the power combining structure of Doherty amplifier with an arbitrary electric length includes the steps of: calculating(201) the ABCD parameters of the impedance transformer and the impedance inverter at the lambda/4 transmission line of the micro-strip structure; calculating(203) the ABCD parameters of the impedance transformer and the impedance inverter of the power connection structure to be transformed; calculating(205) the impedance and the capacitance of the impedance inverter and the impedance transformer; calculating(207) the arbitrary length and the capacitance of the impedance inverter and the impedance transformer in response to the calculated impedance and the capacitance; constructing(209) the impedance inverter and the impedance transformer in response to the calculated transmission length and the capacitor; connecting(211) the impedance inverter and the impedance transformer, and substituting one capacitor for the two capacitors connected at the connection position in parallel; and implementing(213) the impedance inverter and the impedance transformer.

Description

POWER COMBINING METHOD FOR POWER COMBINING STRUCTURE HAVING ARBITRARY ELECTRIC LENGTH FOR DOHERTY AMPLIFIER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Doherty amplifier, and in particular, to improve the power coupling structure of the power coupling unit that combines the outputs of the carrier amplifier and the peak amplifier constituting the Doherty amplifier, and converts them into transmission lines and lumped elements having an arbitrary electrical length. The present invention relates to a power combining method of a Doherty amplifier, which enables miniaturization of an amplifier.

In general, the Doherty Amplifier is a high-efficiency amplifier of a large power transmitter. In general, the Doherty Amplifier improves the anode efficiency by power combination of a Class B amplifier (or Class AB) and a Class C amplifier.

1 is a view illustrating a conventional Doherty amplifier. As shown, the Doherty amplifier 100 includes a carrier amplifier 10 for linearly amplifying a carrier and a peak amplifier for amplifying only a peak signal simultaneously with load modulation. It is composed of (20), it is designed to have the optimum efficiency in order to be able to transfer the maximum output of the two amplifiers to the load resistor (60).

The carrier amplifier 10 operates at the point where the output begins to saturate for maximum linear efficiency, and the peak amplifier 20 is used to maintain the linearity of the output signal when the carrier amplifier begins to saturate.

The Doherty amplifier 100 includes a circuit 30 over 90 ° on an input side and a power combiner 40 on an output side. The 90 ° or more circuit 30 and the power coupler 40 are typically implemented with a microstrip or stripline technique.

The power combiner 40 generally includes an impedance inverter 40a having an impedance of 50 Ω and a quarter wavelength, and also an impedance transformer 40b having a quarter wavelength and an impedance of about 35 Ω. In response to amplifier 10, the carrier and the outputs of peak amplifiers 10, 20 are interconnected.

At this time, if the impedance of the impedance inverter 40a is Z _T , the impedance Z _T2 of the impedance transformer 40b is

Ω.

The 90 ° or more circuit 30 is for compensating for the phase difference between the paths of the carrier amplifier 10 line and the peak amplifier line 20, and preferably has 1/4 wavelength at an impedance of 50 Ω.

As shown in FIG. 1, the Doherty amplifier 100 combines the outputs of the carrier amplifier 10 and the peak amplifier 20 in a combination circuit 50 such as a common node through a λ / 4 power combiner 40. Let's do it.

In general, the bias of the carrier amplifier 10 is operated in class B, the peak amplifier 20 is operated in class C. This allows the peak amplifier to operate from the region where the maximum output level is 6dB back off.

The basic operation principle of the Doherty amplifier 100 may be described as an active load pull due to the output current of the peak amplifier 20. The operation of the Doherty amplifier 100 may be divided into three parts, a low power level region, an intermediate power level region in which load modulation occurs, and a maximum power level region.

1) Low power level range

In the low power level region, the peak amplifier is designed not to operate and to be viewed as an open circuit with an appropriate impedance offset. At this time, the carrier amplifier 2 R _OPT: operating in (R _OPT optimum load impedance of the amplifier), which are operated by a common Class B amplifier (or class AB). Accordingly, the efficiency of the carrier amplifier is simultaneously increased as the output power is increased and saturated at the point of 6dB-off from the maximum output level to reach the maximum efficiency of the ideal class B amplifier.

2) Medium power level range

 In the middle power level region, the carrier amplifier is saturated and operates at maximum efficiency.

When the input power increases to reach the mid-level 6dB-backoff point, the peak amplifier is activated. A current I ₂ supplied by the peak amplifier 20 of the first gives increases the impedance of the low power level (Z _{IT) OPT} value R / 2 as shown in V _IT in R _OPT. Of the carrier amplifier load impedance (Z ₁₎ will have a characteristic impedance (Z ₀₎ the value of R _OPT of the load modulation effect in R 2 in R _{OPT OPT} through the λ / 4 impedance inverter (40a).

3) Maximum power level range

In the maximum power level range, the loads of the carrier amplifier and peak amplifier operate with R _OPT , with each amplifier supplying half of the output power. At maximum power, the efficiency is 78.5%, the ideal Class B efficiency.

Such load modulation is a core operation principle of the Doherty amplifier, and is made through a reactive power coupling structure using an impedance inverter.

For the power coupling structure of the Doherty amplifier, the power coupling structure as shown in FIG. 2 is generally used. This is a structure disclosed in US Patent No. US 5,420,541 (registered May 5,199, Microwave Doherty Amplifier, hereinafter referred to as "Prior Art"), and shows the electrical equivalent circuit of FIG.

FIG. 5 is a circuit diagram showing a power coupling structure used in a conventional Doherty amplifier. As shown in FIG. 5, an impedance inverter 40a used for load modulation of a carrier amplifier is implemented using a 50Ω transmission line. , Electrical length is λ / 4. As shown in Fig. 2, the impedance transformer 42 implemented with a λ / 4 transmission line having a 35Ω impedance of the final output stage has a 25Ω load impedance 50 generated by parallel coupling of the power amplifier and a characteristic impedance of the final output. To match 50Ω. At this time, it is assumed that the power amplifier is matched to 50Ω.

Therefore, the conventional Doherty power coupling structure using the conventional λ / 4 transmission line as disclosed in the prior art has a problem that the physical length of the λ / 4 transmission line makes it difficult to miniaturize the circuit when implementing the circuit.

Accordingly, an object of the present invention for solving the above problems is to improve the power coupling unit for coupling the output of the Doherty amplifier to improve the power coupling unit using a lumped element and a transmission line having an arbitrary electrical length instead of the conventional λ / 4 transmission line The present invention provides a power combining method of a Doherty amplifier, which provides a power combining structure for miniaturizing a Doherty amplifier circuit.

In order to achieve the above object, the present invention combines a carrier amplifier and a peak amplifier, a circuit of 90 ° or more that compensates for the phase difference between the paths of the carrier amplifier and the peak amplifier, and the output of the carrier amplifier and the peak amplifier. A power coupling method for implementing a power coupling structure consisting of an arbitrary electrical length and a concentrating element of a Doherty amplifier having at least a power coupling unit including an impedance inverter and an impedance transformer,

Calculating ABCD parameters of an impedance inverter and an impedance transformer in a λ / 4 transmission line having a microstrip structure according to Equation 1 below;

Calculating ABCD parameters of an impedance inverter and an impedance transformer having a power coupling structure composed of arbitrary electrical lengths and lumped elements according to Equation 2 below;

From the following <Equation 1> and <Equation 2>, the impedance and capacitance satisfying the following <Equation 3> and <Equation 4> of the power coupling structure consisting of the arbitrary electrical length and the concentrated element Calculating for each of the impedance inverter and the impedance transformer;

Constructing an impedance inverter and an impedance transformer composed of the arbitrary electrical length and the lumped element according to impedances and capacitances calculated from Equations 3 and 4 below;

Combining the configured impedance inverter and the impedance transformer, and implementing a power coupling unit by combining an impedance inverter and an impedance transformer composed of an arbitrary electrical length and a lumped element; and having an arbitrary electrical length, characterized in that it comprises a. Provided is a power combining method for a power combining structure of a Doherty amplifier.

<Equation 1>

<Equation 2>

Z ₀ : characteristic impedance, C : capacitance, l : transmission line length, Z : load impedance, Bl = θ

<Equation 3>

<Equation 4>

In addition, the present invention further comprises the step of replacing the two capacitors connected in parallel to the coupling point to which the configured impedance inverter and the impedance transformer are replaced by one capacitor, power of the Doherty amplifier having an arbitrary electrical length. Provided is a power combining method for the coupling structure.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same components have the same reference numerals as much as possible even if they are displayed on different drawings. Detailed descriptions of well-known functions and configurations that are determined to unnecessarily obscure the subject matter of the present invention will be omitted.

3 is an impedance inverter implemented with a λ / 4 microstrip transmission line according to the prior art, and FIG. 4 is an impedance inverter implemented with a transmission line having a certain electrical length and a lumped element according to the power coupling method of the present invention.

The microstrip structure of FIG. 3 having a λ / 4 transmission line may be implemented as an equivalent structure of a transmission line having an arbitrary length and a parallel capacitor, as shown in FIG. 4.

The power coupling structure of the Doherty amplifier implemented according to the present invention can be obtained from the microstrip λ / 4 transmission line according to the prior art of FIG. 3 using the ABCD parameter.

The ABCD parameter of the impedance inverter implemented with a transmission line having an arbitrary length of FIG. 4 and a parallel capacitor is as follows.

Z ₀ : characteristic impedance, C : capacitance, l : transmission line length, Z : load impedance, Bl = θ

Therefore, the condition for two ABCD parameters to be equal is

Because of,

From the above conditions, two λ / 4 transmission lines shown in FIG. 5 may be implemented as transmission lines having two parallel capacitors and arbitrary electrical lengths as shown in FIG. 6.

FIG. 6 is an impedance inverter in which the power coupling structure of FIG. 5 is converted to the power coupling method according to the present invention, and FIG. 7 is a circuit configuration of the power coupling structure used in the Doherty amplification apparatus implemented by the power coupling method according to the present invention. It is also.

As shown in FIG. 6, the impedance inverter 40a and the impedance transformer 40b each having a λ / 4 transmission line must satisfy Equations 3 and 4, respectively. Accordingly, it can be represented by the impedance inverter 70a and the impedance transformer 70b converted into a lumped element composed of a transmission line and a capacitor having an arbitrary electrical length.

FIG. 7 illustrates a power coupling structure of a Doherty amplifier implemented with an impedance inverter 70a and an impedance transformer 70b converted into a lumped element composed of a transmission line and a capacitor having an arbitrary electrical length shown in FIG. 6. .

When the impedance inverter 70a and the impedance transformer 70b, which are converted into a lumped element composed of a transmission line and a capacitor having an arbitrary electrical length, are connected to the coupling point in parallel, two capacitors may be replaced with one capacitor. This makes the circuit simpler to implement.

8 is a flowchart illustrating a power combining method for a power combining structure of a Doherty amplifier according to the present invention, and lists the power combining method of the Doherty amplifier according to the present invention in order.

As shown in FIG. 8, the power coupling method for implementing the power coupling structure of the Doherty amplifier according to the present invention includes an impedance inverter 40a and an impedance transformer in a λ / 4 transmission line of a microstrip structure to be converted in step 201. The ABCD parameter of (40b) is calculated according to <Equation 1>.

Subsequently, ABCD parameters of the impedance inverter 70a and the impedance transformer 70b of the power coupling structure to be converted in step 203 are calculated according to Equation 2 above.

In order to calculate the impedance and capacitance of the power coupling structure to be converted, the two ABCD parameters of Equation 1 and Equation 2 must be the same, and thus, Equation 3 and Equation 4 Impedance and capacitance satisfying? Are calculated for the impedance inverter 70a and the impedance transformer 70b, respectively.

Then, the arbitrary length and capacitor of the impedance inverter 70a and the impedance transformer 70b according to the impedance and capacitance calculated in step 207 are calculated, and the process proceeds to step 209 according to the line length and the capacitor calculated in step 207. Impedance inverter 70a and impedance transformer 70b composed of arbitrary electrical lengths and capacitors are constructed.

Subsequently, the impedance inverter 70a and the impedance transformer 70b are combined in step 211, and the two capacitors connected in parallel to the coupling point are replaced with one capacitor, thereby the impedance inverter 70a and the impedance transformer in step 213. A new power coupling structure by combining 70b provides a power coupling method of a Doherty amplifier in which the electrical length of the power coupling unit, which has been an obstacle to miniaturization of the Doherty amplifier, can be arbitrarily adjusted with the capacitance of a capacitor, which is a lumped element.

On the other hand, in the detailed description of the present invention has been described with reference to specific embodiments, of course, various modifications are possible without departing from the scope of the invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention can reduce the size of the Doherty amplifier by improving the physical length of the λ / 4 transmission line coupling the output of the Doherty amplifier to have an arbitrary electrical length.

In addition, the present invention can more simply configure the circuit by reducing the number of capacitors provided as a lumped element, there is an effect that can reduce the cost.

1 is a block diagram of a Doherty amplifier according to the prior art,

2 is a view showing a power coupling structure of a Doherty amplifier according to the prior art,

3 is an impedance inverter implemented with a λ / 4 microstrip transmission line according to the prior art,

4 is an impedance inverter implemented with a transmission line having a certain electrical length and a concentrator according to the power combining method of the present invention;

5 is a circuit diagram showing a power coupling structure used in the Doherty amplifier according to the prior art,

FIG. 6 is an impedance inverter converting the power coupling structure of FIG. 5 into a power coupling method according to the present invention;

7 is a circuit diagram of a power coupling structure used in the Doherty amplification apparatus implemented by the power coupling method according to the present invention;

8 is a flowchart illustrating a power combining method for a power combining structure of a Doherty amplifier according to the present invention.

Explanation of symbols on the main parts of the drawings

10: carrier amplifier 20: peak amplifier

30: Circuit over 90 °? 40, 70: power coupling portion

40a, 70a: Impedance Inverter 40b, 70b: Impedance Transformer

50: combination circuit 60: load resistance

Claims (2)

A power including a carrier amplifier and a peak amplifier, a circuit of at least 90 degrees that compensates for the phase difference between the paths of the carrier amplifier and the peak amplifier, an impedance inverter and an impedance transformer for coupling the outputs of the carrier amplifier and the peak amplifier A power coupling method for implementing a power coupling structure consisting of an arbitrary electrical length and a lumped element of a Doherty amplifier having at least a coupling portion, Calculating ABCD parameters of an impedance inverter and an impedance transformer in a λ / 4 transmission line having a microstrip structure according to Equation 1 below; Calculating ABCD parameters of an impedance inverter and an impedance transformer having a power coupling structure composed of arbitrary electrical lengths and lumped elements according to Equation 2 below; From the following <Equation 1> and <Equation 2>, the impedance and capacitance satisfying the following <Equation 3> and <Equation 4> of the power coupling structure consisting of the arbitrary electrical length and the concentrated element Calculating for each of the impedance inverter and the impedance transformer; Constructing an impedance inverter and an impedance transformer composed of the arbitrary electrical length and the lumped element according to impedances and capacitances calculated from Equations 3 and 4 below; Combining the configured impedance inverter and the impedance transformer, and implementing a power coupling unit by combining an impedance inverter and an impedance transformer composed of an arbitrary electrical length and a lumped element; and having an arbitrary electrical length, characterized in that it comprises a. Power coupling method for power coupling structure of a Doherty amplifier. <Equation 1> <Equation 2> Z ₀ : characteristic impedance, C : capacitance, l : transmission line length, Z : load impedance, Bl = θ <Equation 3> <Equation 4> The method of claim 1, Power for a power coupling structure of a Doherty amplifier having an arbitrary electrical length, further comprising replacing one capacitor with two capacitors connected in parallel to a coupling point to which the configured impedance inverter and the impedance transformer are coupled. Joining method.