JPH0525421B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a transmitter consisting of a quadrature modulator and a linear amplifier, and in particular, it is possible to achieve excellent linearity by stably applying negative feedback to the modulation input. Regarding the resulting transmitter.

[Prior art and its problems]

When transmitting digital signals, linear modulation methods such as quadrature phase keying (QPSK) are often used. When transmitting such a linearly modulated wave,
In order to keep unnecessary out-of-band radiated power low, a modulator and transmission amplifier with excellent linearity are required.
However, since some kind of nonlinear distortion always exists in actual modulators and amplifiers, it is important to find a way to reduce this distortion. Among these methods, as a method to improve the linearity of the transmission amplifier,
Negative feedback amplification is known in which a part of the output signal is fed back to the input in reverse phase, but this method has the disadvantage that it becomes difficult to apply negative feedback stably as the transmission frequency increases. As a method for stabilizing negative feedback, the method described in Japanese Patent Publication No. 58-27684 ``Narrowband Transmission Negative Feedback Amplifier'' is known. According to this prior art, stability is improved by automatically controlling the phase of the input signal of the amplifier and the feedback signal to 180 degrees. However, in this conventional technology, since feedback is applied at a high frequency or an intermediate frequency, the stability is still insufficient, and there is also a problem in circuit realization that the phase detector must be implemented at a high frequency or an intermediate frequency. .
Furthermore, since this prior art focuses only on the linearity of the amplifier, it is not possible to improve the linearity of the modulator.

[Purpose of the invention]

An object of the present invention is to eliminate such problems in the prior art, to provide a transmitter that stably improves the linearity of both a modulator and an amplifier, and that is easy to implement as a circuit.

[Structure of the invention]

The present invention provides a quadrature modulator having means for inputting in-phase and quadrature modulated input signals, an amplifier for amplifying and transmitting an output signal of the modulator, and a branching part of the output signal of the amplifier. a quadrature detector receiving the obtained signal as input; a signal synthesizing means for negative feedback synthesizing the in-phase and quadrature detection signals, which are two output signals of the quadrature detector, with the in-phase and quadrature modulated input signals, respectively; and the signal synthesizing means. a phase control circuit inserted at any point in a signal path from the output of the means to an input terminal through which the two output signals of the quadrature detector are inputted to the signal combining means; A phase detector having first and second multiplier circuits that multiply the quadrature and in-phase detection signals, respectively, and whose detection output is a signal obtained by subtracting the output signals of the first and second multiplier circuits. By using the output signal of the phase detector as a control signal input of the phase control circuit, the phase difference between the in-phase and quadrature modulation input signals and the in-phase and quadrature detection signals is approximately reduced.
It is characterized by 180° control.

According to the present invention, when a quadrature modulated wave is amplified and transmitted, after performing quadrature detection on a part of the output signal of the amplifier, when negative feedback is applied to the input signal of the modulator in an opposite phase, the input signal of the modulator is In order to automatically maintain the phase difference between the signal and the negative feedback signal at approximately 180 degrees, phase detection is performed in the baseband band, and phase control is performed using this output.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. Input terminals 111 and 11 of this transmitter
2 is a signal synthesis circuit (differential amplifier in this example) 1
21 and 122, respectively, and these signal synthesis circuits are connected to the quadrature modulator 131.
It is connected to the. This quadrature modulator is connected to a high frequency amplifier 150 whose output terminal is connected to a transmission output terminal 160.

The output terminal of the high frequency amplifier 150 is connected to a signal branching circuit 165 and a phase control circuit 170 that constitute a feedback path.
and the quadrature detector 132 to the signal synthesis circuit 121.
and the inverting input terminal of 122.
The input terminals 111, 112 of the transmitter and the output terminal of the quadrature detector 132 in the return path are connected to the phase detector 1.
80 input terminals, respectively. The output terminal of the phase detector 180 is connected to the input terminal of the phase control circuit 170 in the feedback path. A 90° phase difference separation circuit 141 to which an oscillator 140 is connected is connected to the quadrature modulator 131 and the quadrature detector 132.

In a transmitter with such a configuration, input terminal 1
The in-phase modulation input signal x(t), which is the transmission signal input to 11, is input to the non-inverting input terminal of the signal synthesis circuit 121, and the quadrature modulation input signal y(t), which is the transmission signal input to the input terminal 112, is input to the non-inverting input terminal of the signal synthesis circuit 121. ) is input to the non-inverting input terminal of the signal synthesis circuit 122. here,
For example, in the case of digital transmission, the modulated input signals x(t) and y(t) are two independent Nyquist band-limited digital signals. These modulated input signals x
(t) and y(t) are input to the orthogonal modulator 131 and orthogonally modulated. The modulated wave signal m(t) which is the output signal of the orthogonal modulator 131 is amplified by the transmission high frequency amplifier 150 and then transmitted from the transmission output terminal 160. A part of the output signal of the amplifier 150 is inputted to a phase control circuit 170 through a signal branching circuit 165 and subjected to phase control. The high frequency feedback signal r(t), which is the output signal of the phase control circuit 170, is sent to the quadrature detector 132.
orthogonal detection is performed, and baseband signals, that is, in-phase and quadrature detection signals x'(t) and y'(t) are obtained.
These detected signals x'(t), y'(t) are modulated input signals x(t),
It has changed from y(t). Quadrature and in-phase detection signals
A part of y′(t) and x′(t) are respectively sent to the signal synthesis circuit 12.
1,122, and is combined with modulated signals x(t) and y(t). Here, x(t) and x′(t) and y(t) and y′(t)
are almost antiphase (doesn't have to be exactly antiphase)
The phase control circuit 170 and phase detection circuit 180 compensate for the phase shift in the amplifier 150 and the feedback path so that

The outline of the configuration and operation of this embodiment has been explained above, and the configuration and operation of each part will be explained in more detail below.

FIG. 2 is a diagram showing an example of the orthogonal modulator 131. Input terminals 211 and 212 receive an in-phase modulation input signal x(t) from the signal synthesis circuit 121 and a quadrature modulation input signal y(t) from the signal synthesis circuit 122.
are respectively input, the in-phase modulation input signal x(t) is input to the mixer 221, and the orthogonal modulation input signal y(t) is input to the mixer 221.
22. Input terminals 251 and 252
Local oscillation signals, that is, carrier waves whose phases are different from each other by 90 degrees are input to the mixers 221 and 222, respectively. Mixer 221 and 2
At 22, the modulating input signal amplitude modulates the local oscillator signal. The two local oscillation signals are generated by the oscillator 140 and the 90° phase difference separation circuit 141 of FIG. 1 so that their phases are 90° different from each other.
The amplitude-modulated outputs of mixers 221 and 222 are combined by adder circuit 230 and then output to output terminal 240 as orthogonal modulation signal m(t).

FIG. 3 is a diagram showing an example of the quadrature detector 132. The high frequency feedback modulation signal r(t) input from the phase control circuit 170 to the input terminal 310 is split into two branches,
The baseband signal, that is, the in-phase detection signal x′(t ) and quadrature detection signal y'(t) are obtained at output terminals 341 and 342. Note that the local oscillation signal is generated by the oscillator 140 and
It is input from the 90° phase difference separation circuit 141. In-phase and quadrature detection signals detected as above
x'(t) and y'(t) are input to signal synthesis circuits 121 and 122 and phase detector 180, respectively.

FIG. 4 is a diagram showing an example of the phase detector 180. Input terminals 411 and 412 receive in-phase and quadrature modulated input signals x(t) and y(t) from input terminals 111 and 112 in FIG. is input. Input terminals 421 and 422 have
Quadrature and in-phase detection signals from the quadrature detector 132
y'(t) and x'(t) are input to first and second multiplication circuits 431 and 432, respectively. These modulated input signals and detection signals are multiplied by first and second multiplication circuits 431 and 432, respectively, and then subtracted by subtraction circuit 440, and a detection signal is outputted to output terminal 450. As will be described later, this detection signal represents the magnitude of the phase rotation of the amplifier 150 and the feedback path, and is input to the phase control circuit 170 as a control signal. The phase control circuit 170 automatically compensates for the phase shift in the amplifier 150 and the feedback path, and the signal synthesis circuit 1
The feedback signals input to 21 and 122 are controlled so that they always have opposite phases. In addition, the phase control circuit is
Although circuits using variable capacitance diodes are known, any circuit may be used as long as it can control the phase shift.

The above operation will be explained in more detail using mathematical formulas. The orthogonal modulated signal m(t) output from the orthogonal modulator 131 is expressed by the modulated input signals x(t) and y(t) as follows.

m(t)=x(t)cosω _c ty(t)sinω _c t …(1) Here, _ωc is the angular frequency of the carrier wave, and the first
This is the oscillation frequency of the oscillator 140 in the figure.

On the other hand, the high frequency feedback signal r(t) input from the output terminal of the amplifier 150 to the quadrature detector 132 via the signal branching circuit 165 is expressed as follows.

r(t)=x′(t)cosω _c t−y′(t)sinω _c t …(2) Here, x′(t) and y′(t) are the quadrature detector 132 as described above. They are in-phase and quadrature detection signals, respectively. The detected signals x'(t) and y'(t) change from the modulated input signals x(t) and y(t) as follows due to the phase rotation of the amplifier 150 and the feedback path. Here, θ
indicates the magnitude of the phase rotation.

x′(t)=x(t)cosθ+y(t)sinθ…(3) y′(t)=−x(t)sinθ+y(t)cosθ…(4) From these equations, sinθ=x′(t )y(t)−y′(t)x(t)/x ² (t)+y ² (t)…(5) is obtained. The denominator of the above equation is positive and |θ|
When <<1, sinθ can be approximated by θ, so (5)
The numerator of the equation can be the phase detection output. The phase detector 180 shown in FIG. 4 realizes the calculation of the numerator of equation (5). By using the output signal of the phase detector 180 as a control signal for the phase control circuit 170, the phase shift in the amplifier 150 and the feedback path is automatically compensated, and the signal synthesis circuits 121, 12
It is possible to control the feedback signals inputted to 2 to always have opposite phases.

As explained above, according to this embodiment, phase detection is performed using the baseband signal, feedback synthesis is performed in the baseband band, and negative feedback is applied to the input of the modulator.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and it goes without saying that various modifications and changes can be made within the scope of the present invention. For example, in the above embodiment, the phase control circuit 1
70 is provided in the high frequency feedback path from the output terminal of the amplifier 150 to the quadrature detector 132, but it may be provided anywhere in the feedback loop from the output terminal to the input terminal of the signal synthesis circuits 121, 122. It is clear that it is good.

〔Effect of the invention〕

As explained above, since the present invention applies negative feedback to the input of the modulator, it is possible to improve distortion not only in the amplifier but also in the modulator. Also,
In the present invention, since phase detection is performed on the baseband signal, it is easy to implement a phase detection circuit, and since feedback synthesis is performed in the baseband band, it is possible to perform feedback synthesis stably.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram of a quadrature modulator used in the embodiment of FIG. 1, and FIG. 3 is a block diagram of a quadrature modulator used in the embodiment of FIG. FIG. 4 is a block diagram of a phase detector used in the embodiment of FIG. 1. 121, 122...signal synthesis circuit, 131...
Quadrature modulator, 132... Quadrature detector, 150...
Amplifier, 170...phase control circuit, 180...phase detector.

Claims (1)

[Claims] 1 A quadrature modulator having means for inputting in-phase and quadrature modulation input signals, an amplifier for amplifying and transmitting the output signal of the modulator, and a signal obtained by branching a part of the output signal of the amplifier. a quadrature detector which receives as an input, a signal synthesizing means for negative feedback synthesizing the in-phase and quadrature detection signals, which are two output signals of the quadrature detector, with the in-phase and quadrature modulated input signals, respectively, and an output of the signal synthesizing means. a phase control circuit inserted at any point in the signal path from and a phase detector which has first and second multiplier circuits that multiply the in-phase detection signal, and whose detection output is a signal obtained by subtracting the output signals of the first and second multiplier circuits. , by using the output signal of the phase detector as the control signal input of the phase control circuit,
A transmitter characterized in that the phase difference between the in-phase and quadrature modulation input signals and the in-phase and quadrature detection signals is controlled to approximately 180 degrees.