JP2009267514A - Cartesian feedback transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a Cartesian feedback transmitter which has an increased distortion compensating amount while keeping stability in loop. <P>SOLUTION: The Cartesian feedback transmitter includes: adders 20, 21 for adding the in-phase component and orthogonal component of a base band input signal to be input and a feedback signal together; low-pass filters 2, 3 for limiting the band of the base band signal through the adders; an orthogonal modulator 4 for orthogonally modulating the output signals of the low-pass filters; an amplifier 6 for amplifying a modulation signal modulated by the orthogonal modulator; a signal branch means 7 for branching the output signal of the amplifier; and an orthogonal demodulator 100 for orthogonally demodulating the output signals of the amplifier branched by the signal branching means and negatively feeding back the signals to the adders as feedback signals. The transmitter includes a negative group delay circuit 9 in one of the signal transmission routes between transmission routes from the adders 20, 21 to the signal branching means 7, and feedback routes from the signal branching means 7 to the adders 20, 21. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a Cartesian feedback transmitter that reduces distortion by feeding back a part of an output with added nonlinear distortion of an amplifier to a baseband signal.

  As a conventional Cartesian feedback transmitter, an adder that adds in-phase and quadrature components of the input baseband input signal to the feedback signal, a low-pass filter that limits the band of the baseband signal via the adder, The quadrature modulator that quadrature modulates the output signal of the low-pass filter, the amplifier that amplifies the modulation signal modulated by the quadrature modulator, the signal branching means that branches the output signal of the amplifier, and the signal branching means A quadrature demodulator that quadrature demodulates the output signal of the amplifier and negatively feeds back as a feedback signal to the adder, and inputs the modulation signal obtained by orthogonally modulating the output signal of the low-pass filter by the quadrature modulator to the amplifier (For example, see Patent Document 1).

  In this Cartesian feedback transmitter, the in-phase component and the quadrature component of the baseband input signal input from the baseband signal input terminal are input to the adder, and are added to the feedback signal which is the output of the quadrature demodulator by the adder. Is done. The added baseband signal is subjected to frequency band restriction by a low-pass filter, then input to a quadrature modulator, modulated, and converted into an in-phase component and a quadrature component of the modulated signal. Further, the modulated signal is amplified by an amplifier and then output from the output terminal via the signal branching means.

  A part of the output signal from the amplifier is fed back by the signal branching means and input to the quadrature demodulator. The signal input to the quadrature demodulator is demodulated by the quadrature demodulator and converted into the in-phase component and the quadrature component of the feedback signal. Then, the in-phase component and the quadrature component of the feedback signal are input to the adder. The feedback signal output from the quadrature demodulator has nonlinear distortion of the amplifier, but the nonlinear distortion can be compensated by feeding back this feedback signal to the adder as described above.

  By the way, this Cartesian feedback transmitter is designed so that the phase around a loop in which a baseband input signal is input from an input terminal and returned to the adder as a feedback signal is 180 degrees.

For example, when the baseband signal input terminal is Port1, the output terminal that outputs the output signal from the signal branching means is Port2, and the output terminal when the circuit is disconnected by providing an output terminal at the output of the quadrature demodulator is Port3, When the path from Port 1 to Port 3 is defined as an open loop, the output signal V _FB from Port 3 is expressed by Expression (1).

V _FB = Re [A · V _in ] (1)
However, in Formula (1), A = a ₀ · exp ^jθ0 (2)
V _in = r _in · exp ^jφin (3)

In the above equation, A is the open loop complex gain, a ₀ is the open loop gain, and θ ₀ is the open loop phase. Also, r _in is the amplitude of the input signal, and φ _in is the phase of the input signal. FIG. 9 shows an example of an open-loop complex gain A.

Now, as shown in FIG. 9, when the open-loop complex gain A is decomposed into the _in- phase component A _x and the quadrature component A _y of the phase φ _in of the input signal, the following equation is obtained.
A _x = Re [A] = a ₀ · cos θ ₀ (4)
A _y = Re [A] = a ₀ · sin θ ₀ (5)

In the above equation, if the input signal and the phase component A _x is 1 or more, the loop is unstable. That is, the condition that makes the loop unstable is expressed by Equation (6).
A _x ≧ 1 (6)
When this is expressed in dB, the equation (7) is obtained.
A _x ≧ 0 (dB) (7)

FIG. 10 shows an example of frequency characteristics of the open loop gain a ₀ and the phase θ ₀ in the conventional Cartesian feedback transmitter. FIG. 11 shows the _in- phase component A _x of the open loop gain a ₀ and the phase φ _in of the input signal. A _x is obtained using the above-described equation (4). For example, at point A, the open loop gain a ₀ is about −22 dB and the open loop phase θ ₀ is about 0 deg. At this time, in FIG. 11, _{A x} is can be seen that about -22 dB. From FIG. 11, this Cartesian feedback transmitter operates stably because A _x <0 dB and conditional expression (7) that makes the loop unstable is not satisfied.

JP-A-6-303045

However, if a Cartesian feedback transmitter is applied to an amplifier that requires more linearity, the loop gain must be increased in order to increase the distortion compensation amount, resulting in a frequency band where the loop becomes unstable. come. For example, in order to increase the distortion compensation amount, it is assumed that the loop gain is increased as shown in FIG. FIG. 13A shows the _in- phase component A _x of the open loop gain a ₀ and the phase φ _in of the input signal, and FIG. 13B is an enlarged view of FIG. 13A. In FIG. 13B, the frequency band between B and C is A _x ≧ 0 dB and satisfies the formula (7), so the loop becomes unstable.

  The present invention has been made in view of the above points, and an object thereof is to obtain a Cartesian feedback transmitter capable of increasing the distortion compensation amount while maintaining the stability of the loop.

  A Cartesian feedback transmitter according to the present invention includes an adder that adds an in-phase component and a quadrature component of an input baseband input signal to a feedback signal, and a low-pass signal that band-limits the baseband signal via the adder. A filter, a quadrature modulator that quadrature modulates the output signal of the low-pass filter, an amplifier that amplifies the modulation signal modulated by the quadrature modulator, a signal branching unit that branches the output signal of the amplifier, In a Cartesian feedback transmitter comprising an orthogonal demodulator that orthogonally demodulates the output signal of the amplifier branched by the signal branching means and negatively feeds back as a feedback signal to the adder, from the adder to the signal branching means A negative group delay circuit is provided in the signal transmission path of either the transmission path or the feedback path from the signal branching means to the adder It is characterized in.

  According to the present invention, by providing the negative group delay circuit in either the transmission path from the adder to the signal branching means or the feedback path from the signal branching means to the adder, a normal low-pass signal can be obtained. Phase delay caused by components such as filters, quadrature modulators, amplifiers, and quadrature demodulator can be reduced by using the phase lead characteristics of negative group delay circuits, and stability can be improved. Since the open loop gain can be increased by improving the distortion, the distortion compensation amount can be increased while maintaining the stability of the Cartesian feedback transmitter.

Embodiment 1 FIG.
1 is a block diagram showing a configuration of a Cartesian feedback transmitter according to Embodiment 1 of the present invention. The Cartesian feedback transmitter according to Embodiment 1 shown in FIG. 1 includes adders 20 and 21 that add an in-phase component I and a quadrature component Q of an input baseband input signal to a feedback signal, and adders 20 and 21. The low-pass filters 2 and 3 for band-limiting the baseband signal via the quadrature, the quadrature modulator 4 for quadrature-modulating the output signals of the low-pass filters 2 and 3, The amplifier 6 to be amplified, the signal branching means 7 for branching the output signal of the amplifier 6, the attenuator 8 for attenuating a part of the output signal from the amplifier 6 branched by the signal branching means 7, and the attenuator 8 A negative group delay circuit 9 for giving a negative group delay to the output, an attenuator 10 for attenuating the output signal from the negative group delay circuit 9, and an output signal via the attenuator 10 being orthogonally demodulated and added Return to vessels 20 and 21 And a quadrature demodulator 100 for negatively feeding back as No.. In addition, 1 is an input terminal and 11 is an output terminal.

  Here, the feature of the first embodiment is that a negative group delay circuit 9 is provided in the signal transmission path from the signal branching means 7 to the quadrature demodulator 100. FIG. 2 is a diagram showing a configuration of negative group delay circuit 9 in the first embodiment. As shown in FIG. 2, the negative group delay circuit 9 includes two series resonance circuits each including an inductor Ls, a capacitor Cs, and a resistor Rs connected in parallel to the signal transmission path, and an inductor Lp, a capacitor Cp, and a resistor. One parallel resonant circuit composed of Rp is connected in series with a signal transmission path and arranged in a π-type.

  Next, the operation will be described. Similarly to the Cartesian feedback transmitter according to the conventional example, the Cartesian feedback transmitter according to Embodiment 1 also adds the in-phase component I and the quadrature component Q of the baseband input signal input from the baseband signal input terminal 1. Input to the devices 20 and 21. Adders 20 and 21 add the feedback signal that is the output of quadrature demodulator 100 from in-phase component I and quadrature component Q, and output in-phase component I and quadrature component Q of the added baseband signal. The sum baseband signal is input to the quadrature modulator 4 after the frequency band is limited to a low frequency by the low-pass filters 2 and 3. The signal input to the quadrature modulator 4 is modulated by the quadrature modulator 4 and converted into an in-phase component I and a quadrature component Q of the modulated signal. This modulated signal is input to the amplifier 6.

  Further, this modulated signal is amplified by the amplifier 6 and then output from the output terminal 11 via the signal branching means 7. A part of the output signal from the amplifier 6 by the signal branching means 7 is attenuated by the attenuator 8 and then input to the negative group delay circuit 9.

  Here, the negative group delay circuit 9 having the configuration shown in FIG. 2 utilizes the resonance phenomenon of the LC parallel resonance circuit and the LC series resonance circuit, and locally generates a negative group delay in the vicinity of the resonance frequency. For example, FIG. 3 shows the amplitude and phase characteristics of the negative group delay circuit 9 shown in FIG. In FIG. 3, the horizontal axis represents the frequency f, and the vertical axis represents the amplitude and phase characteristics of the pass characteristic S21. In the negative group delay circuit 9 shown in FIG. 2, the phase increases as the frequency f increases in the vicinity of the resonance frequency (here, 1 GHz) as shown in FIG. 3, so dθ / df becomes positive.

Here, the group delay GD can be obtained from Equation (8).
GD = −dθ / dω = −dθ / d (2πf) (8)
In equation (8), it can be seen that a negative group delay occurs when dθ / df> 0. For this reason, the circuit shown in FIG. 2 has a negative group delay in the vicinity of the resonance frequency.

  The negative group delay circuit 9 shown in FIG. 2 has a π-type configuration of an LC parallel resonance circuit and an LC series resonance circuit, but this may be a T type. Further, the LC parallel resonance circuit and the LC series resonance circuit may be freely combined to be multistaged. Further, a configuration using at least one of the LC parallel resonance circuit and the LC series resonance circuit may be used.

FIG. 4 shows an example of open loop gain and phase frequency characteristics in the first embodiment. FIG. 8 shows the _in- phase component A _x of the open loop gain a ₀ and the phase φ _in of the input signal according to the conventional example shown in comparison with FIG. 4, and FIG. FIG. In FIG. 8B, in the conventional Cartesian feedback transmitter, A _x ≧ 0 dB in the frequency band between B and C, and the loop is unstable, but in the first embodiment, A _x It can be seen that <0 dB and the loop is stable even between B and C.

  Returning to FIG. 1, the output signal of the negative group delay circuit 9 is input to the quadrature demodulator 100 via the attenuator 10. The signal input to the quadrature demodulator 100 is demodulated by the quadrature demodulator 100 and converted into the in-phase component I and the quadrature component Q of the feedback signal. Then, the in-phase component I and the quadrature component Q of the feedback signal are input to the adders 20 and 21. The feedback signal output from the quadrature demodulator 100 has nonlinear distortion of the amplifier 6. The nonlinear distortion is compensated by feeding back this feedback signal to the adders 20 and 21 as described above.

  As described above, according to the first embodiment, the negative group delay circuit 9 is provided so that components such as the normal low-pass filters 2 and 3, the quadrature modulator 4, the amplifier 6, and the quadrature demodulator 100 are used. The purpose is to reduce the generated phase delay by using the phase advance characteristic of the negative group delay circuit 9 and to improve the stability. Further, when the stability is improved, the open-loop gain can be increased as shown in FIG. 4, so that the distortion compensation amount can be increased while maintaining the stability of the Cartesian feedback transmitter.

  In the first embodiment, the negative group delay circuit 9 is provided in the feedback path between the attenuators 8 and 10. However, the transmission path or signal branch from the adders 20 and 21 to the signal branching means 7 is provided. The signal transmission path may be provided in any one of the feedback paths from the means 7 to the adders 20 and 21, and the same effect as in the first embodiment is obtained.

Embodiment 2. FIG.
6A and 6B illustrate a negative group delay circuit 9 according to the second embodiment of the present invention. FIG. 6A shows a configuration of the negative group delay circuit 9, and FIG. It is a figure which shows the amplitude and phase characteristic of this group delay circuit 9. As shown in FIG. 6A, in the second embodiment, a series connection circuit of a short stub composed of a resistor and a microstrip line is connected in parallel to the signal transmission line, and is shown in FIG. The negative group delay circuit 9 in the Cartesian feedback transmitter is configured. Note that the negative group delay circuit 9 shown in FIG. 6A uses one signal transmission line in which a short stub composed of a resistor and a microstrip line is connected in parallel. Any number of these may be combined. Alternatively, the negative group delay circuit 9 may be configured with only a short stub having a resistive component.

  Next, the operation will be described. In FIG. 6B, the horizontal axis represents the frequency f, and the vertical axis represents the amplitude and phase characteristics of the pass characteristic S21. In the negative group delay circuit 9 shown in FIG. 6A, the phase increases as the frequency f increases in the vicinity of the resonance frequency (here, 2 GHz, 4 GHz) as shown in FIG. dθ / df is positive. For this reason, a negative group delay occurs from the equation (8). This negative group delay circuit 9 can obtain a negative group delay characteristic in the vicinity of the frequency where the line length of the short stub is l = λ / 2, λ, 3λ / 2,.

  The operation when the negative group delay circuit 9 is used is the same as that of the first embodiment. By including the negative group delay circuit 9 in the second embodiment, it is possible to increase the distortion compensation amount while maintaining the stability of the Cartesian feedback transmitter with a simple configuration.

Embodiment 3 FIG.
7A and 7B illustrate a negative group delay circuit 9 according to Embodiment 3 of the present invention. FIG. 7A is a diagram showing the configuration of the negative group delay circuit 9, and FIG. It is a figure which shows the amplitude and phase characteristic of this group delay circuit 9. As shown in FIG. 7 (a), in the third embodiment, an open stub series connection circuit composed of a resistor and a microstrip line is connected in parallel to the signal transmission line, as shown in FIG. The negative group delay circuit 9 in the Cartesian feedback transmitter is configured. The negative group delay circuit 9 shown in FIG. 7A uses a single signal transmission line in which an open stub composed of a resistor and a microstrip line is connected in parallel. Any number of these may be combined. Further, the negative group delay circuit 9 may be configured by only an open stub having a resistive component.

  Next, the operation will be described. In FIG. 7B, the horizontal axis represents the frequency f, and the vertical axis represents the amplitude and phase characteristics of the pass characteristic S21. In the negative group delay circuit 9 shown in FIG. 7A, as shown in FIG. 7B, the phase increases as the frequency f increases in the vicinity of the resonance frequency (here, 1 GHz, 3 GHz, 5 GHz). Therefore, dθ / df is positive. For this reason, a negative group delay occurs from the equation (8). This negative group delay circuit has a negative group delay characteristic in the vicinity of the frequency where the line length of the open stub is 1 = λ / 4, 3λ / 4, 5λ / 4,.

  The operation when this negative group delay circuit is used is the same as that of the first embodiment. By including the negative group delay circuit 9 in the third embodiment, the distortion compensation amount can be increased while maintaining the stability of the Cartesian feedback transmitter with a simple configuration.

Embodiment 4 FIG.
FIG. 8 shows a structure of negative group delay circuit 9 according to the fourth embodiment of the present invention. In the fourth embodiment, a series connection circuit of an open stub and a resistor having different line lengths (l ₁ ≠ l ₂ ), ie, microstrip lines having different resonance frequencies, is connected in parallel to the signal transmission line. Thus, the negative group delay circuit 9 in the Cartesian feedback transmitter shown in FIG. 1 is configured.

  In the first and second embodiments, even when the circuit is multistaged, the resonance frequencies may be set to different frequencies as in the fourth embodiment. The operation in the fourth embodiment is the same as that in the first embodiment. By including the negative group delay circuit 9 in the fourth embodiment, two or more series connection circuits of stubs and resistors having different line lengths are used, and dθ / df of each stub and resistance series connection circuit is positive. By shifting the frequency range to be wide and widening the frequency band in which dθ / df is positive as a whole, the negative group delay characteristic is widened, and distortion compensation is performed while maintaining the stability of the Cartesian feedback transmitter. The amount can be increased.

  In the fourth embodiment, as the negative group delay circuit 9, a series connection circuit of a resistor and an open stub is connected in parallel to the signal transmission path, and the resistor and the open stub have a line length. A series connection circuit of different open stubs connected in parallel to the signal transmission path was used, but a series connection circuit of a resistor and a short stub connected in parallel to the signal transmission path, and a resistance The short stub may be a series connection circuit of short stubs having different line lengths connected in parallel to the signal transmission path, and the same effect can be obtained.

It is a block diagram which shows the structure of the Cartesian feedback transmitter which concerns on Embodiment 1 of this invention. FIG. 2 is a circuit diagram illustrating an example of a configuration of a negative group delay circuit 9 illustrated in FIG. 1. FIG. 3 is a diagram showing amplitude and phase characteristics of the negative group delay circuit 9 shown in FIG. 2. It is a figure which shows an example of the frequency characteristic of the gain and phase of an open loop in Embodiment 1 of this invention. FIG. 5 is a diagram showing an _in- phase component A _x of an open loop gain a ₀ and a phase φ _{in of} an input signal according to a conventional example shown in comparison with FIG. 4. A negative group delay circuit 9 according to a second embodiment of the present invention will be described. FIG. 6A shows a configuration of the negative group delay circuit 9, and FIG. 6B shows a negative group delay circuit. 9 is a diagram showing the amplitude and phase characteristics of FIG. 7 illustrates a negative group delay circuit 9 according to Embodiment 3 of the present invention. FIG. 7A is a diagram showing a configuration of the negative group delay circuit 9, and FIG. 7B is a negative group delay circuit. 9 is a diagram showing the amplitude and phase characteristics of FIG. It is a figure which shows the structure of the negative group delay circuit 9 concerning Embodiment 4 of this invention. It is a figure for demonstrating operation | movement of the conventional Cartesian feedback transmitter, and is a figure which shows an example of the complex gain A of an open loop. Is a diagram illustrating an example of the open loop gain a ₀ and phase theta ₀ of the frequency characteristic of a conventional Cartesian feedback transmitter. It is a diagram illustrating a phase component A _x of the phase phi _in the open-loop gain a ₀ and the input signal in a conventional Cartesian feedback transmitter. FIG. 10 is a diagram for explaining the operation of a conventional Cartesian feedback transmitter, and shows a case where the loop gain is increased in order to increase the distortion compensation amount. The operation of the conventional Cartesian feedback transmitter will be described. FIG. 13A shows an _in- phase component A _x of the open loop gain a ₀ and the phase φ _in of the input signal, and FIG. FIG. 14 is an enlarged view of FIG.

Explanation of symbols

  1 Baseband signal input terminal, 2, 3 low-pass filter, 4 quadrature modulator, 6 amplifier, 7 signal branching means, 8 attenuator, 9 negative group delay circuit, 10 attenuator, 11 output terminal, 100 quadrature demodulation , 20, 21 Adder.

Claims (10)

An adder that adds the in-phase and quadrature components of the input baseband input signal to the feedback signal;
A low-pass filter for band-limiting the baseband signal via the adder;
A quadrature modulator for quadrature modulating the output signal of the low-pass filter;
An amplifier for amplifying the modulation signal modulated by the quadrature modulator;
Signal branching means for branching the output signal of the amplifier;
A Cartesian feedback transmitter comprising: an orthogonal demodulator that quadrature demodulates the output signal of the amplifier branched by the signal branching means and negatively feeds back as a feedback signal to the adder;
A Cartesian feedback transmission characterized in that a negative group delay circuit is provided in either the transmission path from the adder to the signal branching means or the feedback path from the signal branching means to the adder. Machine. The Cartesian feedback transmitter of claim 1,
As the negative group delay circuit, at least one series resonance circuit composed of a capacitor, an inductor and a resistor connected in parallel to the signal transmission path is used. The Cartesian feedback transmitter of claim 1,
The Cartesian feedback transmitter characterized by using at least one of the negative group delay circuits in which a parallel resonance circuit composed of an inductor, a capacitor and a resistor is connected in series to the signal transmission path. The Cartesian feedback transmitter of claim 1,
As the negative group delay circuit, a series resonance circuit composed of a capacitor, an inductor and a resistor is connected in parallel to the signal transmission path, and a parallel resonance circuit composed of an inductor, a capacitor and a resistance is used as the signal transmission path. A Cartesian feedback transmitter characterized in that at least one of those connected in series is used. The Cartesian feedback transmitter of claim 1,
As the negative group delay circuit, at least one of a series connection circuit of a resistor and a short stub connected in parallel to the signal transmission path is used. The Cartesian feedback transmitter of claim 1,
As the negative group delay circuit, at least one of a short stub having a resistive component and connected in parallel to a signal transmission path is used. The Cartesian feedback transmitter of claim 1,
As the negative group delay circuit, at least one of a series connection circuit of a resistor and an open stub connected in parallel to the signal transmission path is used. The Cartesian feedback transmitter of claim 1,
As the negative group delay circuit, at least one of open stubs having resistive components connected in parallel to the signal transmission path is used. The Cartesian feedback transmitter of claim 1,
As the negative group delay circuit, a series connection circuit of resistors and open stubs connected in parallel to the signal transmission path, and a series connection circuit of open stubs having different line lengths from the resistors and the open stubs, A Cartesian feedback transmitter characterized by using one connected in parallel to the signal transmission path. The Cartesian feedback transmitter of claim 1,
As the negative group delay circuit, a series connection circuit of resistors and short stubs connected in parallel to the signal transmission path, and a series connection circuit of short stubs having different line lengths from the resistors and the short stubs, A Cartesian feedback transmitter characterized by using one connected in parallel to the signal transmission path.

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