Technical Field

The present invention relates to a Doherty amplifier, and more particularly, to an apparatus for compensating for phase of a Doherty amplifier.

Background Art

A Doherty amplifier is one of amplifiers used in a high efficiency modulation method for a high power transmitter and mainly improves efficiency by a combination of a B grade amplifier, a C grade amplifier, and an impedance inverting circuit.

FIG. 1 is a block diagram of a conventional Doherty amplifier. Referring to FIG. 1 , the conventional Doherty amplifier includes a 90° phase splitter 110, a carrier amplifier 120, a peak (or peaking) amplifier 130, and a quarter wave transformer 140.

The Doherty amplifier adopts a method of connecting the carrier amplifier 120, and the peak amplifier 130 in parallel using the quarter wave transformer 140 (λ/4 lines). The amount of current output from the peak amplifier 130 as a load varies according to a power level. Accordingly, efficiency is improved by adjusting a load impedance of the carrier amplifier 120.

In the 90° phase splitter 110, a splitter splits an input signal into two signals so that one signal is input to the carrier amplifier 120 and the other signal is input to the peak amplifier 130. The signal input to the peak amplifier 130 is delayed by 90° so that a delay time difference from the signal input to the carrier amplifier 120 is compensated for.

Although the 90° phase compensation is possible in theory, in an actual circuit, since the delayed time is not exactly 90° due to various constituent components existing in the circuit, phase equivalent to the actual difference is to be compensated for.

The 90° phase splitter 110 is mainly implemented with passive devices and using a 3dB hybrid coupler. The carrier amplifier 120 and the peak amplifier 130 include input matching, a drive end transistor, inter-stage matching, an output end transistor, and output matching network.

However, the 90° phase splitter 110 made of the passive devices requires a large size of the passive devices to be implemented at a lower frequency and i

integration thereof is not easy.

Disclosure of Invention

To solve the above and/or other problems, the present invention provides a Doherty amplifier using an active phase splitter which can compensate for phase with only active devices, and moreover, finely compensate for phase by adding an inductor L and/or a capacitor C.

According to an aspect of the present invention, a Doherty amplifier using an active phase splitter in which a carrier amplifier and a peak amplifier are connected in parallel using a quarter wave transformer (λ/4 line), the Doherty amplifier comprising an active phase splitter, wherein the active phase splitter comprises a buffer amplifier splitting an input signal into a first route and a second route and compensating for a phase difference, a base terminal of the buffer amplifier is connected to an input signal terminal so that an output of a collector terminal of the buffer amplifier forms the first route and an output of an emitter terminal of the buffer amplifier forms the second route, and a signal output from the first route is input to the carrier amplifier and a signal output from the second route is input to the buffer amplifier.

According to another aspect of the present invention, a Doherty amplifier using an active phase splitter in which a carrier amplifier and a peak amplifier are connected in parallel using a quarter wave transformer (λ/4 line), the Doherty amplifier comprising an active phase splitter, wherein the active phase splitter comprises a first transistor and a second transistor to split an input signal into a first route and a second route and compensate for a phase difference, the first transistor and the second transistor have a differential pair structure, an output of a collector terminal of the first transistor forms the first route and an output of a collector terminal of the second transistor forms the second route, and a signal output from the first route is input to the carrier amplifier and a signal output from the second route is input to the buffer amplifier.

According to another aspect of the present invention, a Doherty amplifier using an active phase splitter in which a carrier amplifier and a peak amplifier are connected in parallel using a quarter wave transformer (λ/4 line), the Doherty amplifier comprising an active phase splitter, wherein the active phase splitter comprises a first transistor and a second transistor to split an input signal into a first route and a second route and compensate for a phase difference and has a structure formed of a base common amplifier in which an input signal terminal is connected to an emitter terminal of the first

transistor and an emitter common amplifier in which the input signal terminal is connected to a base terminal of the second transistor, an output of a collector terminal of the first transistor forms the first route and an output of a collector terminal of the second transistor forms the second route, and a signal output from the first route is input to the carrier amplifier and a signal output from the second route is input to the buffer amplifier.

Brief Description of the Drawings

FIG. 1 is a block diagram of a conventional Doherty amplifier; FIG. 2 is a block diagram of a Doherty amplifier using an active phase splitter according to an embodiment of the present invention;

FIGS. 3A through 3D are circuit diagrams of an active phase splitter according to an embodiment of the present invention;

FIGS. 4A through 4D are circuit diagrams of an active phase splitter according to another embodiment of the present invention; and

FIGS. 5A through 5D are circuit diagrams of an active phase splitter according to yet another embodiment of the present invention.

Best Mode for Carrying Out the Invention FIG. 2 is a block diagram of a Doherty amplifier using an active phase splitter according to an embodiment of the present invention. Referring to FIG. 2, the Doherty amplifier using an active phase splitter includes an active phase splitter 210, a carrier amplifier 220, a peak amplifier 230, and a quarter wave transformer 240.

The active phase splitter 210 is formed based on a buffer amplifier and an inductor L and/or a capacitor C can be added to perform fine phase compensation or generate a phase difference to a desired degree. Conventionally, the buffer amplifier can be used instead of the first stage of the carrier amplifier 220 and the peak amplifier 230 consisting of two or more amplification stages.

The configuration using the buffer amplifier only or the configuration using the buffer amplifier and the L and/or C is a structure in which a high frequency monolithic microwave circuit (MMIC) is possible, and can decrease the size of the amplifier.

The active phase splitter 210 splits an input signal into two output signals so that an output signal on a first route is input to the carrier amplifier 220 and the other output signal on a second route is input to the peak amplifier 230. The signal input to the

peak amplifier 230 is delayed by 90° so that a delay time difference from the signal input to the carrier amplifier 220 is compensated for.

Alternately, among the two signals split by the active phase splitter 210, the output signal on the first route can be input to the peak amplifier 230 and the output signal on the second route can be input to the carrier amplifier 230. Here, the active phase splitter 210 is designed such that the signal input to the peak amplifier 230 and the signal input to the carrier amplifier 220 have a phase difference of about 90°.

FIGS. 3A through 3D are circuit diagrams of an active phase splitter according to an embodiment of the present invention. FIG. 3A shows a circuit having a single device structure for compensating for phase using a transistor Q30 only that is an active device. Among two signals output to a collector terminal (or a first route) and an emitter terminal (or a second route) of the transistor Q30, the output signal on the first route is connected to a contact point 35 of FIG. 2 and input to the carrier amplifier

220 while the output signal on the second route is connected to a contact point 45 of FIG. 2 and input to the peak amplifier 230.

Alternately, the output signal on the first route can be connected to the contact point 45 and input to the peak amplifier 230 while the output signal on the second route can be connected to the contact point 35 and input to the carrier amplifier 220.

FIG. 3B shows a circuit for compensating for phase using the transistor Q30 that is an active device and an inductor L1 and a capacitor C1. In the circuit, the L1 and

C1 are connected to the collector terminal of the transistor Q30 so that finer phase compensation is possible or a phase difference to a desired degree can be generated.

If necessary, only one of the L1 and C1 can be used.

FIG. 3C shows a circuit in which an inductor L2 and a capacitor C2 are added to the emitter terminal of the transistor Q30 that is an active device to perform fine phase compensation or generate a phase difference to a desired degree. If necessary, only one of the L2 and C2 is added to compensate for the phase difference.

FIG. 3D shows a circuit for compensating for phase using the transistor Q30 that is an active device, the L1 and C1 , and the L2 and C2. The L1 and C1 are connected to the collector terminal of the transistor Q30 and the L2 and C2 are connected to the emitter terminal thereof so that finer phase compensation is possible or a phase difference to a desired degree is generated.

That is, the L1 and C1 connected to the collector terminal of the transistor Q30 are connected to the contact point 35 in series while the L2 and C2 connected to the

emitter terminal of the transistor Q30 are connected to the contact point 45 in series. By adjusting the values of the L1 and C1 and the l_2 and C2, the phase difference of 90° between the signals input to the carrier amplifier 220 and the peak amplifier 230 is generated. In FIGS. 3B through 3D, each circuit is composed by connecting the inductor and the capacitor to the transistor Q30 that is an active device. In the present embodiment, one of the inductor and capacitor is basically used. However, both the inductor and capacitor can be used or the inductor and capacitor can be further added.

FIGS. 4A through 4D are circuit diagrams of an active phase splitter according to another embodiment of the present invention. FIG. 4A shows a circuit having a differential amplification structure for compensating for phase using a first transistor Q41 and a second transistor Q42. Among two signals input to a collector terminal of a first transistor Q41 (or a first route) and a collector terminal of a second transistor Q42 (or a second route), the output signal on the first route is connected to the contact point 35 and input to the carrier amplifier 220 while the output signal on the second route is connected to the contact point 45 and input to the peak amplifier 230.

Alternately, the output signal on the first route can be connected to the contact point 45 and input to the peak amplifier 230 while the output signal on the second route can be connected to the contact point 35 and input to the carrier amplifier 220. FIG. 4B shows a circuit in which an inductor L1 and a capacitor C1 are connected to the collector terminal of the first transistor Q41 only so that finer phase compensation is performed or a phase difference to a desired degree is generated.

FIG. 4C shows a circuit in which an inductor L2 and a capacitor C2 are connected to the collector terminal of the second transistor Q42 only so that finer phase compensation is performed or a phase difference to a desired degree is generated.

FIG. 4D shows a circuit in which the L1 and C1 are connected to the collector terminal of the first transistor Q41 and the L2 and C2 are connected to the collector terminal of the second transistor Q42 so that finer phase compensation is performed or a phase difference to a desired degree is generated.

That is, the L1 and C1 connected to the collector terminal of the first transistor Q41 are connected to the contact point 35 in series while the L2 and C2 connected to the emitter terminal of the second transistor Q42 are connected to the contact point 45 in series. By adjusting the values of the L1 and C1 and the L2 and C2, the phase

difference of 90° between the signals input to the carrier amplifier 220 and the peak amplifier 230 is generated.

In FIGS. 4B through 4D, each circuit is composed by connecting the inductor and the capacitor to the transistors Q41 and/or Q42 that are active devices. In the present embodiment, one of the inductor and capacitor is basically used. However, both the inductor and capacitor can be used or the inductor and capacitor can be further added.

FIGS. 5A through 5D are circuit diagrams of an active phase splitter according to yet another embodiment of the present invention. FIG. 5A shows a circuit having a common base CB/common emitter CE structure, in which an output signal on a first route of a base common amplifier, to which an input signal terminal 10 and an emitter terminal of a first transistor Q51 are connected, is connected to the contact point 35 and input to the carrier amplifier 220. An output signal on a second route of an emitter common amplifier, to which the input signal terminal 10 and a base terminal of a second transistor Q52 are connected, is connected to the contact point 45 and input to the peak amplifier 220.

Also, the circuit can be designed such that the output signal on the first route is connected to the contact point 45 and input to the peak amplifier 230 and the output signal on the second route is connected to the contact point 35 and input to the carrier amplifier 220.

When a phase difference is generated insufficiently with the active device only or in order to more accurately compensate for a phase difference, as shown in FIG. 5B, an inductor L1 and/or a capacitor C1 can be connected only between the input signal terminal 10 and the emitter terminal of the first transistor Q51. Also, when a phase difference is generated insufficiently with the active device only or in order to more accurately compensate for a phase difference, as shown in FIG. 5C, an inductor L2 and/or a capacitor C2 can be connected only between the input signal terminal 10 and the base terminal of the second transistor Q52.

FIG. 5D shows a circuit in which the L1 and/or C1 are connected between the input signal terminal 10 and the emitter terminal of the first transistor Q51 and the L2 and/or C2 are connected between the input signal terminal 10 and the base terminal of the second transistor Q52, so that finer phase difference is generated or a phase difference is generated as much as a circuit designer desires.

The L1 and/or C1 are connected in series between the input signal terminal 10

and the emitter terminal of the first transistor Q51 and to the contact point 35, and the L2 and/or C2 are connected in series between the input signal terminal 10 and the base terminal of the second transistor Q52 and to the contact point 45.

By adjusting the values of the L1 and C1 and the L2 and C2, the phase difference of 90° between the signals input to the carrier amplifier 220 and the peak amplifier 230 is generated.

In FIGS. 5B through 5D, each circuit is composed by connecting the inductor and the capacitor to the transistors Q51 and/or Q52 that are active devices. In the present embodiment, one of the inductor and capacitor is basically used. However, both the inductor and capacitor can be used or the inductor and capacitor can be further added.

While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Industrial Applicability

As described above, according to the present invention, since a phase compensation circuit is made using an active device, the size taken by the phase compensation circuit is reduced much so that the phase compensation circuit can be integrated in a high frequency monolithic microwave circuit (MMIC). Also, since the active device constituting the phase compensation circuit can replace the first stage of the carrier amplifier and the peak amplifier, the carrier amplifier and the peak amplifier can be easily designed.