JP5732014B2 - Doherty amplifier - Google Patents

Description

  The present invention relates to a Doherty amplifier as a high-frequency power amplifier. More specifically, the tuning frequency of the primary side and the secondary side of the transformer is shifted by connecting the amplifiers with a transformer and adjusting the tuning frequency. The present invention relates to a Doherty amplifier designed to increase the bandwidth of the amplifier.

  In recent years, mobile communication and wireless LAN (Local Area Network) have made remarkable progress. In particular, the explosive spread of mobile phones and the accompanying infrastructure development have reduced power consumption not only for mobile terminals but also for base stations. It has been requested. Therefore, there is an increasing demand for an improvement in efficiency and linearity for amplifiers used for transmission in base stations.

  However, in a typical amplifier, there is a trade-off between efficiency and linearity, and efficiency is proportional to the input level to the amplifier. Therefore, high efficiency is not obtained until the amplifier output approaches the maximum output power, so it is difficult to achieve amplifier linearity. Therefore, a high-efficiency, low-distortion amplifier has been developed by combining high-efficiency signal amplification techniques such as Doherty Amplifiers with distortion compensation techniques such as low distortion and feedforward. Has been. This Doherty amplifier basically combines a class AB carrier amplifier and a class C peak amplifier, and combines the outputs of these amplifiers to realize high efficiency amplification.

  FIG. 1 is a circuit diagram for explaining a Doherty amplifier using a conventional emitter amplifier. In FIG. 1, reference numeral 1 denotes a distributor, 2 denotes a main amplifier (carrier amplifier), 3 denotes a peak amplifier, and 4 and 5 denote 90. ° Shows phase shifter. This conventional Doherty amplifier includes a distributor 1 that distributes an input signal into two input signals, a main amplifier 2 that is directly inputted with an output signal of the distributor 1, and a first delay that delays the output phase of the distributor 1 by 90 °. 1 90 ° phase shifter 4, a peak amplifier 3 having the output signal of the first 90 ° phase shifter 4 as an input signal, and a second 90 ° that shifts the output phase of the main amplifier 2 by 90 °. FIG. 3 is a circuit configuration diagram that achieves high efficiency by using the fact that the output of the peak amplifier 3 and the output of the second 90 ° phase shifter 5 are in phase with the phase shifter 5. In the Doherty amplifier shown in FIG. 1, each of the main amplifier 2 and the peak amplifier 3 outputs a current, is added by a load resistor R, is converted into a voltage, and is output.

2A and 2B are circuit configuration diagrams for explaining the Doherty amplifier disclosed in Non-Patent Document 1, and FIG. 2A is a circuit configuration for explaining the gain reduction of the Doherty amplifier. FIG. 2 and FIG. 2B are diagrams showing an equivalent circuit of the peak amplifier of FIG.
Since the output of the main amplifier 2 needs to pass through the second 90 ° phase shifter 5, it is disclosed that the phase becomes opposite to the berth current of the peak amplifier 3 and the efficiency of the peak amplifier 3 is reduced.

  FIG. 3 is a circuit configuration diagram for explaining the Doherty amplifier disclosed in Non-Patent Document 1, similarly to FIGS. 2 (a) and 2 (b). It is disclosed that a variable phase shifter 6 is inserted between the input of the main amplifier 2 and the distributor 1 so that the output component of the main amplifier 2 is not canceled out of the base current of the peak amplifier 3.

  Further, for example, the one described in Patent Document 1 relates to a high-power amplifier for amplifying a modulated wave signal in a high frequency band, and in particular, realizes a high-power amplifier having high efficiency even in an operating state with a large back-off. The present invention relates to a Doherty amplifier. In this patent document 1, a variable attenuator and a variable phase shifter are provided on the input side of the peak amplifier, and are arranged on the input side of the variable attenuator and peak amplifier. Since a variable phase shifter is provided, the gain difference between the carrier amplifier and the peak amplifier and the difference in the passing phase amount are compensated, and the output power of the carrier amplifier and the output power of the peak amplifier at the output end are combined. This can be carried out satisfactorily, and the output power and efficiency of the entire microwave Doherty amplifier can be improved.

JP 2002-124840 A

"Linearity Improvement of HBT-based Doherty Power Amplifiers Based on a Simple Analytical Model" Yu Zhao et al., 4 names IEEE 2006 pp. 877-880

  However, in recent years, in radar / moving object detection, it has been required to keep a high output constant over a wide range of ambient conditions in order to realize a maximum detection distance. In the prior art as described above, the amplification level decreases due to the wraparound from the main amplifier to the peak amplifier, the phase difference occurs because the bias conditions of the main amplifier and the peak amplifier are different, and further, There is a problem that third-order intermodulation distortion deteriorates due to phase interference between the amplifier and the peak amplifier.

  The present invention has been made in view of such problems. The object of the present invention is to tune the primary side and the secondary side of the transformer by connecting an amplifier with a transformer and adjusting the tuning frequency. It is an object of the present invention to provide a Doherty amplifier in which the frequency is shifted to increase the bandwidth of the amplifier.

The present invention has been made to achieve such an object. The invention according to claim 1 is directed to a distributor to which an input signal is distributed, and one of the distributed signals from the distributor is an input. A main amplifier, a first phase shifter that delays the phase of the other distributed signal from the distributor by 90 degrees, a peak amplifier that receives a signal from the first phase shifter, and A second phase shifter that delays the phase of the signal from the main amplifier by 90 degrees; and an adder that adds the signal from the peak amplifier and the signal from the second phase shifter; and at least one of the peak amplifier, the first amplifying unit and said a first differential pair of load primary transformer and the primary side transformer and paired secondary side including a first differential pair a first transformer portion including a transformer, the secondary side transformer Comprising a second amplifier including a second differential pair to be continued, and using the phase control signal to the phase variable signal from at least one of the main amplifier and the peak amplifier, the primary side At least one of the transformer and the load of the secondary transformer is variable.

Also, an invention according to claim 2, in the invention described in claim 1, wherein at least one of the main amplifier and the peak amplifier, which is connected upstream of the first amplifier, the primary side transformer and said And a second transformer including a secondary transformer paired with the primary transformer.

The invention according to claim 3 is the invention according to claim 1 , wherein at least one of the main amplifier and the peak amplifier is a load on a differential pair of the second amplifier and the primary transformer. And a third transformer including a secondary transformer paired with the primary transformer.
The invention according to claim 4 is the invention according to any one of claims 1 to 3 , wherein the load of the primary transformer and the secondary transformer is a variable capacitor. To do.

  According to the present invention, a Doherty amplifier is realized in which the tuning frequency of the primary side and the secondary side of the transformer is shifted to increase the bandwidth of the amplifier by connecting the amplifier with a transformer and adjusting the tuning frequency. can do. Further, by designing the transformer so that the tuning frequencies on the primary and secondary sides of the transformer are shifted, it is possible to simultaneously achieve a wide band of the amplifier. In addition, by designing the plurality of transformers with different tuning frequencies, it is possible to simultaneously achieve a wide band of amplifiers. Further, by relaxing the parasitic capacitance of the cascode intermediate node, the parasitic pole can be moved to the high frequency side, and a wide band can be achieved at the same time. Furthermore, the Doherty amplifier usually has an effect that the main amplifier can be realized by Class AB and the peak amplifier can be realized by Class C.

It is a circuit block diagram for demonstrating the Doherty amplifier using the conventional emitter amplifier. (A), (b) is a circuit block diagram for demonstrating the Doherty amplifier currently disclosed by the nonpatent literature 1. FIG. FIG. 3 is a circuit configuration diagram for explaining the Doherty amplifier disclosed in Non-Patent Document 1, similarly to FIGS. It is a circuit block diagram for demonstrating embodiment of the Doherty amplifier which concerns on this invention. FIG. 5 is a circuit configuration diagram illustrating a specific example 1 of the main amplifier and the peak amplifier illustrated in FIG. 4. (A), (b) is the figure which represented each of the primary side and secondary side of a transformer with the LCR parallel circuit. (A) thru | or (d) is a figure which shows the gain and phase frequency characteristic of the path | route of a main amplifier and a peak amplifier. It is an enlarged view of Fig.7 (a). It is an enlarged view of FIG.7 (b). It is an enlarged view of FIG.7 (c). It is an enlarged view of FIG.7 (d). FIG. 5 is a circuit configuration diagram illustrating a specific example 2 of the main amplifier and the peak amplifier illustrated in FIG. 4. FIG. 5 is a circuit configuration diagram illustrating a specific example 3 of the main amplifier and the peak amplifier illustrated in FIG. 4.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 4 is a circuit configuration diagram for explaining an embodiment of the Doherty amplifier according to the present invention. In the figure, 11 is a distributor, 12 is a main amplifier (with transformer), 13 is a peak amplifier (with transformer), 14 is a first 90 ° phase shifter, 15 is a second 90 ° phase shifter, and 16 is An adder is shown.

The Doherty amplifier according to the present embodiment realizes variable phase without adding a new circuit as in Non-Patent Document 1 described above. The circuit resulting from the load asymmetry between transformers has the following advantages: 1) Since there is no new element insertion, circuit loss is minimal. 2) Generally, since _Q L> _{Q C} is 10GHz or more, than the addition of DC-Cut capacity, small loss is better to implement the AC coupling using a Trans. 3) At a high frequency, the circuit scale can be expected to be reduced so that L itself is not small.

This will be described with reference to FIG.
The highly linear Doherty amplifier shown in FIG. 4 includes a distributor 11 to which an input signal is distributed, a main amplifier 12 to which one of the signals distributed from the distributor 11 is input, and a distribution from the distributor 11. The first phase shifter 14 that delays the phase of the other signal by 90 degrees, the peak amplifier 13 to which the signal from the first phase shifter 14 is input, and the phase of the signal from the main amplifier 12 are 90 degrees. A second phase shifter 15 for delaying and an adder 16 for adding the signal from the peak amplifier 13 and the signal from the second phase shifter 15 are provided.

  The main amplifier 12 and the peak amplifier 13 are composed of a transformer and an amplifier, respectively, and a phase difference is generated between the main amplifier 12 and the peak amplifier 13 by utilizing the difference between the primary and secondary transformer loads. Is.

FIG. 5 is a circuit configuration diagram showing a specific example 1 of the main amplifier and the peak amplifier shown in FIG. In the figure, reference numeral 20 denotes a first transformer section, 21 denotes a differential load transformer (primary side), 22 denotes a differential load transformer (secondary side), and 23 denotes a differential pair amplifier.
In the first embodiment, at least one of the main amplifier 12 and the peak amplifier 13 includes a first amplifying unit 23 including a differential pair, a primary transformer 21 and a primary transformer 21 that are loads of the differential pair, A first transformer section 20 including a pair of secondary transformers 22, and at least one of the loads of the primary transformer 21 and the secondary transformer 22 is variable.

That is, the differential pair amplifying unit 23 in FIG. 5 inputs a differential pair, and the primary side of the transformer is mounted on the load unit, and the secondary side of the transformer is an output terminal. The coupling coefficient between the primary side and the secondary side of the transformer is k, and the differential output phase can be changed by making the load of the first transformer unit 20 variable using the phase control signal.
6A and 6B are diagrams showing the primary side and the secondary side of the transformer as LCR parallel circuits, respectively, and FIG. 6A shows the primary side models of the main amplifier and the peak amplifier, FIG. 6B is a diagram illustrating a simulation test circuit. Note that the LCR parallel circuit in FIG. 6A corresponds to the LCR circuit in FIG. In FIG. 6B, LCR_L indicates the secondary side of the main amplifier, LCR_M indicates the primary side of the main amplifier and the peak amplifier, and LCR_H indicates the secondary side of the peak amplifier. LCR_L, LCR_M, and LCR_H are simulated to indicate that the phase can be varied without changing the gain.

  6A and 6B, a model is used in which the load is connected in parallel on the primary side and the secondary side. The primary side load is common to the main amplifier and the peak amplifier, and the secondary side load is the 4 × primary side of the main amplifier and the 1/4 × primary side of the peak amplifier. The primary and secondary load conditions of the main and peak amplifiers are shown in Table 1.

  FIGS. 7A to 7D are diagrams showing the gain / phase frequency characteristics of the main amplifier and the peak amplifier, and the state of the phase / gain change is confirmed by simulation. FIG. 7A is a diagram showing that the frequency is different by about 2 GHz at a phase of 180 ° between the main amplifier and the peak amplifier, which is a general characteristic, and FIG. 7B is a diagram showing a signal result of LCR_H alone. FIG. 7C is a diagram showing a signal result of LCR_M alone, and FIG. 7D is a diagram showing an overall (Sim) result of LCR_L alone.

In the figure, fl is a secondary side of the main amplifier, fm is a primary side of the main amplifier and the peak amplifier, and fh is a secondary side of the peak amplifier. N1PH (dashed line) fl / fm indicates the phase characteristic of the main amplifier path, and N2PH (one-dot chain line) fm / fh indicates the phase characteristic of the peak amplifier path.
8 to 11 are enlarged views corresponding respectively to FIGS. 7A to 7D. That is, FIG. 8 is an enlarged view of FIG. 7A, and FIG. 9 is an enlarged view of FIG. 7B. 10 and 10 are enlarged views of FIG. 7C, and FIG. 11 is an enlarged view of FIG. 7D.

  In the figure, N1DB (solid line) is the gain characteristic of the main amplifier, N1PH (dashed line) is the phase characteristic of the main amplifier, N2DB (one-dot chain line) is the gain characteristic of the peak amplifier, and N2PH (two-dot chain line) is the phase characteristic of the peak amplifier. Show.

FIG. 12 is a circuit configuration diagram showing a specific example 2 of the main amplifier and the peak amplifier shown in FIG. In the figure, reference numeral 30 is a first transformer section, 31 is a differential load transformer (primary side), 32 is a differential load transformer (secondary side), 33 is a first differential pair amplifier, and 34 is a first transformer. The amplifier 35 is a second load, 36 is a second differential pair amplifier, and 37 is a second amplifier.
In the second embodiment, at least one of the main amplifier 12 and the peak amplifier 13 further includes a second amplifier 37 including a second differential pair amplifier 36 to which the secondary transformer 32 is connected.

The second embodiment shows a case where the amplifiers are connected in cascade. In the second embodiment, the circuit configuration diagram shown in FIG. 12 is used for at least one of the main amplifier and the peak amplifier. It is necessary to adjust the phase difference between the current path and the peak amplifier path.
The input is input to the first differential pair amplifier 33 that constitutes the input unit of the first amplifier 34 and is output to the first load of the first amplifier 34. The first load is configured as the primary side of the transformer, and the secondary side is connected to the second differential pair amplifier 36 that is the input of the second amplifier 37. The second amplifier 37 is composed of a second differential pair amplifier 36 and a second load 35, and a connection terminal between the second differential pair amplifier 36 and the second load 35 is connected to the outside as an output. Used for connection.

The phase control signal is applied only to the primary side of the transformer. The same voltage is applied to the variable capacitors C _2P and C _2N on the secondary side of the transformer. The variable capacity on the primary side of the transformer is V _CIP ≠ V _CIN V _CIP is a C _1P phase control signal, and V _CIN is a C _1N phase control signal. It is assumed that the CV characteristics of C _1P and C _1N are equal and the capacitance value increases in proportion to the voltage. The phase difference between P _1N and N _1N is 180 °, and so-called differential signals are input. _Let L _1P = L _1N = L _2P = L _2N = L.

When V _CIP = V _CIN , the phase difference between V _1P and V _1N , and further V _2P and V _2N is 180 °, and the differential amplifiers are connected in cascade.
When V _CIP > V _CIN , L _1P · C _1P > L _1P · C _1P , the phase on the V _1P side is “increase in phase lag”, and the phase on the V _1N side is kept in the relationship “decrease in phase lag”. To the input of the peak amplifier. Originally, there was a phase difference of 180 °, so that it greatly interfered with the base input of the peak amplifier and deteriorated linearity and gain. However, the phase difference ≠ 180 °, and both linearity and gain were improved.

When V _CIP <V _CIN , L _1P · C _1P <L _1P · C _1P . At this time, as in the case of V _CIP > V _CIN , the relationship of the phase difference of 180 ° is broken, so that the linearity / gain is improved.
Below, it _{demonstrates as L1P} = _L1N = _L2P = _L2N = L. On the primary side of the transformer, cascade connection of L _1P and L _1N and cascade connection of C _1P and C _1N are arranged in parallel, and the capacitance value of C _1P and C _1N can be increased or decreased by a phase control signal. The secondary side of the transformer has the same configuration as the primary side, and the coupling coefficient between the primary side and the secondary side is k.

The phase of the amplifier is changed by changing the capacitance of at least one of C _1P and C _1N or C _2P and C _2N of the amplifier having such a configuration.
That is, in the configuration of the second embodiment shown in FIG. 12, the amplifier is used as at least one of the main amplifier and the peak amplifier, and the system is connected between the main amplifier system (path) and the peak amplifier system (path). A phase difference is generated / adjusted, and the main amplifier signal shown in FIG. 2 is reduced from suppressing the base current of the peak amplifier, thereby improving the linearity of the Doherty amplifier. Further, since it can be considered that the base signal level of the peak amplifier is prevented from being lowered, it contributes to the improvement of the gain and output power of the Doherty amplifier.

  FIG. 13 is a circuit configuration diagram showing a specific example 3 of the main amplifier and the peak amplifier shown in FIG. In the figure, reference numeral 40 denotes a first transformer section, 41 denotes a differential load transformer (primary side), 42 denotes a differential load transformer (secondary side), 43 denotes a first differential pair amplifier, and 44 denotes a first transformer. Amplifier, 45 is a second transformer section, 46 is a differential load transformer (primary side), 47 is a differential load transformer (secondary side), 48 is a second differential pair amplifier, and 49 is a second amplifier. , 50 is a third transformer section, 51 is a differential load transformer (primary side), and 52 is a differential load transformer (secondary side).

At least one of the main amplifier 12 and the peak amplifier 13 is connected to the preceding stage of the first amplifier 44, and includes a primary transformer 46 and a secondary transformer 47 including a secondary transformer 47 paired with the primary transformer 46. 45.
At least one of the main amplifier 12 and the peak amplifier 13 includes a primary transformer 51 that is a load of a differential pair of the second amplifier 49 and a secondary transformer 52 that is paired with the primary transformer 51. 3 transformer units 50.

The third embodiment shows a case where two amplifiers are connected in cascade. In the implementation of the third embodiment, the circuit configuration diagram shown in FIG. 13 is used for at least one of the main amplifier and the peak amplifier. It is necessary to adjust the phase difference between the main amplifier path and the peak amplifier path.
The input is input to the first differential pair amplifier 43 via the first transformer unit 40 that constitutes the input unit of the first amplifier 44, and the first load 46 of the first amplifier 44 is primary-ordered. Is input to the second differential pair amplifier 48 via the second transformer unit 45 constituting the side, and further amplified, the second load 51 of the second amplifier 49 is connected to the primary side. Is output via the third transformer 50 constituting the.

In the following description, it is _assumed that L _1P = L _1N = L _2P = L _2N = L _3P = L _3N = L _4P = L _4N = L _5P = L _5N = L _6P = L _6N = L. On the other hand, all the capacitive elements are variable capacitive elements, and at least one of them is increased or decreased by a phase control signal. The first transformer, the second transformer, and the third transformer, which are the three transformers shown in FIG. 13, are cascaded on the primary side of L _XP and L _XN (X = 1 to N), C _XP And C _XN cascade connection (X = 1 to N), L and C are arranged in parallel, and the coupling coefficient between the primary side and the secondary side is k. The configuration of the secondary side of the transformer is similar to the primary side. With such a configuration, the phase of the amplifier is changed by changing the capacitance.

  That is, in the configuration of the third embodiment shown in FIG. 13, an amplifier is used as at least one of the main amplifier and the peak amplifier, and between the main amplifier system (path) and the peak amplifier system (path). A phase difference is generated / adjusted, and the main amplifier signal shown in FIG. 2 is reduced from suppressing the base current of the peak amplifier, thereby improving the linearity of the Doherty amplifier. Further, since it can be considered that the base signal level of the peak amplifier is prevented from being lowered, it contributes to the improvement of the gain and output power of the Doherty amplifier.

1,11 Divider 2 Main amplifier (carrier amplifier)
3 Peak amplifier 4, 5 90 ° phase shifter 6 Variable phase shifter 12 Main amplifier (with transformer)
13 Peak amplifier (with transformer)
14 First 90 ° phase shifter 15 Second 90 ° phase shifter 16 Adder 20, 30, 40 First transformer section 21, 31, 41, 46, 51 Differential load transformer (primary side)
22, 32, 42, 47, 52 Differential load transformer (secondary side)
23 differential pair amplifiers 33, 43 first differential pair amplifiers 34, 44 first amplifier 35 second loads 36, 48 second differential pair amplifiers 37, 49 second amplifier 45 second transformer section 50 Third transformer section

Claims (4)

A distributor to which the input signal is distributed;
A main amplifier to which one of the distributed signals from the distributor is input;
A first phase shifter that delays the phase of the other distributed signal from the distributor by 90 degrees;
A peak amplifier to which a signal from the first phase shifter is input;
A second phase shifter that delays the phase of the signal from the main amplifier by 90 degrees;
An adder for adding the signal from the peak amplifier and the signal from the second phase shifter;
Wherein at least one of the main amplifier and the peak amplifier includes a first amplifying unit including a first of the differential pair, the first load is a primary transformer and the primary transformer and a pair of differential pairs A first transformer section including a secondary transformer, and a second amplifier including a second differential pair to which the secondary transformer is connected ,
At least one of the loads of the primary transformer and the secondary transformer is made variable using a phase control signal that makes the phase of the signal from at least one of the main amplifier and the peak amplifier variable. Doherty amplifier. At least one of the main amplifier and the peak amplifier is connected to a preceding stage of the first amplifier, and includes a primary transformer and a second transformer unit including a secondary transformer paired with the primary transformer. The Doherty amplifier according to claim 1, further comprising: At least one of the main amplifier and the peak amplifier includes a third transformer section including a primary transformer that is a load of a differential pair of the second amplifier and a secondary transformer that is paired with the primary transformer; The Doherty amplifier according to claim 1, further comprising: The primary-side transformer and load the secondary side transformer having the Doherty amplifier according to any one of claims 1 to 3, characterized in that a variable capacitance element.

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