JP2000036767A - Transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide equipment capable of fault detection, even during the stop of a transmitter by detecting the amplitude value of output through the self-diagnosis of whether or not the high frequency circuit part of the transmitter is normal, judging the normality of a circuit by comparing this amplitude value with a normal value, stopping transmission in the case of fault and monitoring the transmission output level at the time of transmission and stopping the transmission during an abnormality. SOLUTION: One part of output from a power amplifier 7 is extracted by a directional coupler 8, this is detected by a detection circuit 28, and the detected signal is A/D-converted by an A/D converter 21 and sent to a control circuit 2'. The control circuit 2' compares the output amplitude value of the detected signal with an output amplitude value, which is stored in an amplitude table 23' at the normal time of the power amplifier 7. When this value does not settle within an allowable error range, the control circuit 2' judges that a fault lies in the transmitter and performs self-diagnosis, without executing the transmission. Then, the control circuit 2' changes over switches 15-20, links the output of the power amplifier 7 to a dummy load 26, and does not allow the output signal of the power amplifier 7 to be transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fault detection of a transmitter using a feedback system.

[0002]

2. Description of the Related Art Conventionally, in a digital radio system, a linear modulation method has been widely used from the viewpoint of improving frequency use efficiency. However, in the linear modulation method, when a signal is amplified by a power amplifier, a transmission signal spectrum is deteriorated due to a deviation (linear characteristic) from a linear characteristic of a circuit including the power amplifier. In order to reduce the deterioration of the transmission signal spectrum, it is necessary to compensate for non-linearity related to the amplitude or phase distortion of the power amplifier. One of the realizing means is a Cartesian feedback type compensation circuit.

FIG. 2 shows an example of a conventional transmitter using a Cartesian feedback type compensation circuit. 27 is a baseband signal generation circuit, 5 is a D / A converter, 12 is an adder, 3 is a loop filter, 4 is a quadrature modulator, 6 is a preamplifier, 7 is a power amplifier, 13 is a main circuit, and 8 is directional coupling. Bowl, 9
Is an attenuator, 11 is a quadrature demodulator, 14 is a feedback circuit, 1 is an output terminal, 22 is an oscillator, 28 is a detection circuit, 21 is an A / D converter, 2 is a control circuit, and 23 is an amplitude table. Here, the main circuit 13 is a part composed of a loop filter 3, a quadrature modulator 4, a preamplifier 6, and a power amplifier 7, and the feedback circuit 14 is a directional coupler 8, an attenuator 9, and a quadrature demodulator 11.
There is a part that consists of.

First, the function as a normal transmitter is as follows. In FIG. 2, a baseband signal generation circuit
The in-phase component I and the quadrature component Q of the baseband signal output from 27 are D / A-converted by the D / A converter 5 and then input to the addition input of the adder 12, respectively. The adder 12
Are passed through a loop filter 3 and input to a quadrature modulator 4. The quadrature modulator 4 quadrature-modulates the in-phase component I and the quadrature component Q of the input baseband signal with the output frequency of the oscillator 22, and outputs the quadrature-modulated signal. The quadrature modulated signal is input to a preamplifier 6, then amplified by a power amplifier 7, and output from an output terminal 1 via a directional coupler 8.
On the other hand, part of the output of the power amplifier 7 is taken out by the directional coupler 8, attenuated by the attenuator 9, and sent to the quadrature demodulator 11. The quadrature demodulator 11 quadrature-demodulates the transmitted signal at the output frequency of the oscillator 22 and sends it to the subtraction input terminal of the adder 12 as the in-phase component I and the quadrature component Q of the baseband signal. Accordingly, the adder 12 applies negative feedback to the in-phase component I and the quadrature component Q of the main circuit 13, respectively.

Since the transmitter using the Cartesian type feedback compensation circuit as described above has a negative feedback configuration,
An equivalent circuit as shown in FIG. 3 is conceivable. FIG. 3 is a block diagram showing an example of an equivalent circuit of the negative feedback circuit. FIG. 3 illustrates the relationship between the stability of the output of the transmitter and the change in gain with respect to the stability of the amount of improvement in distortion. In FIG. 3, the gain of the main circuit 13 (the loop filter 3, the quadrature modulator 4, the preamplifier 6, and the power amplifier 7 in FIG. 2) is A, and the feedback circuit 14 (the directional coupler 8, the attenuator 9, and the quadrature demodulator 11). The gain of β,
Assuming that the input is X, the output is Y, and the amount of nonlinear distortion of the main circuit 13 is D, the input-output relational expression can be expressed as Expression (1). Y = ｛A / (1 + A ・ β)｝ X + D / (1 + A ・ β) = (1 / β) ・ X + D / (A ・ β) (∵A ・ β≫1) 1) When the product A · β of the gain of the main circuit 13 and the feedback circuit 14 is sufficiently large, the input signal is multiplied by 1 / β, and the nonlinear distortion D of the main circuit 13 is
The output is multiplied by 1 / (A · β). Therefore, by applying the negative feedback, the nonlinear distortion D is improved to 1 / (A · β). That is, the compensation of the nonlinear distortion D is determined by the gain A of the main circuit 13 and the gain β of the feedback circuit 14.

A transmitter using such a Cartesian feedback type compensation circuit has taken measures against failure detection by adopting a circuit configuration for monitoring the output level of the power amplifier 7 as shown in FIG. 2, for example. That is, when the transmitter is transmitting, monitoring is performed according to the following procedures (1) and (2). (1) A part of the output of the power amplifier 7 is extracted by the directional coupler 8 and detected by the detection circuit 28. The signal detected by the detection circuit 28 is converted into a digital value by the A / D converter 21 and sent to the control circuit 2. (2) The control circuit 2 calculates the amplitude value of the detected signal,
A comparison is made with the output amplitude value of the power amplifier 7 in a normal state, which is stored in the amplitude table 23 in advance. As a result of the comparison,
If the error does not fall within the allowable error range, the transmitter determines that the transmitter is out of order, and the control circuit 2 stops transmitting the transmitter.

[0007]

In the above-mentioned prior art,
In order to detect the failure of the transmitter, it is necessary to compare the output amplitude value of the power amplifier with the normal amplitude value stored in the amplitude table. However, in order to perform the comparison, the transmitter must be transmitting, and if the transmitter is not transmitting, the failure cannot be detected. A first object of the present invention is to provide a transmitter capable of detecting a failure even when the transmitter is not transmitting. A second object of the present invention is to provide a transmitter capable of easily finding a failure point when the transmitter fails.

[0008]

According to the present invention, there is provided a self-diagnosis circuit for diagnosing whether or not a high-frequency circuit section (a preamplifier, a power amplifier, and an attenuator) of a transmitter is normal. First, by performing self-diagnosis before transmission, the amplitude value of each output of the high-frequency circuit unit is detected, and the output amplitude value is compared with the amplitude value in a normal state stored in the amplitude table. Judge whether each circuit is normal, do not transmit at the time of failure, monitor the transmission output level at the time of transmission, do not transmit if abnormal, perform self-diagnosis, This makes it possible to easily find a failure point.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. The reference numerals used in FIG. 1 are those in FIG.
Those having the same functions as those in FIG. Other, 1
3 'is the main circuit, 14' is the feedback circuit, 15-20 are switches, 10
Is an A / D converter, 2 'is a control circuit, 23' is an amplitude table, and 26 is a dummy load. Further, the preamplifier 6, the power amplifier 7, and the attenuator 9 constitute a high-frequency circuit unit. In the normal mode of the transmitter, the switches 15 to 20 are on the A side, and constitute a compensation circuit for the nonlinear distortion D of the Cartesian loop.

First, a self-diagnosis is performed before transmission, a failure of each circuit constituting the high-frequency circuit is detected, and if there is no failure, normal operation is performed. The operation of the transmitter during the normal operation is the same as that described in the related art, and a description thereof will be omitted. During normal operation, a part of the output of the power amplifier 7 is partially
At the detection circuit 28, and detects the detected signal.
A / D conversion is performed by the A / D converter 21 and sent to the control circuit 2 '. The control circuit 2 'compares the output amplitude value of the detected signal with the normal output amplitude value of the power amplifier 7 stored in the amplitude table 23'. If this does not fall within the allowable error range, the control circuit 2 'determines that the transmitter is faulty and performs a self-diagnosis without transmitting.

In the self-diagnosis mode of the present invention, first, the control circuit 2 'switches the switches 15 to 20 as shown in FIG.
Also, the gain of the loop filter 3 is switched to 0 dB, and the output of the power amplifier 7 is connected to the dummy load 26. By switching from the output terminal 1 and connecting the dummy load 26, the output signal of the power amplifier 7 is not transmitted. That is, the baseband signal generation circuit 27 generates a baseband signal during normal transmission, generates a self-diagnosis signal during self-diagnosis, and the gain of the loop filter 3 has a value of, for example, 20 dB during normal transmission. Sometimes, if the gain remains at that value, the signal will saturate,
dB.

A self-diagnosis circuit is constructed as described above,
A DC voltage is applied to the in-phase component input side of the quadrature modulator 4 and 0 V is applied to the quadrature component input side, and the quadrature modulator 4 outputs a sine wave. This sine wave is input as a self-diagnosis signal to each circuit, and each circuit constituting the high-frequency circuit section is diagnosed from the amplitude value of the output.

An example of some self-diagnosis modes will be described below. The diagnosis control circuit 2 'of the preamplifier 6 switches the switches 15 to 20 as shown in FIG. 4 and switches the gain of the loop filter 3 to 0 dB to form a self-diagnosis circuit, which is connected to the in-phase component input side of the quadrature modulator 4. A DC voltage is applied, and 0 V is applied to the quadrature component input side. As a result, the quadrature modulator 4 outputs a sine wave. This sine wave is input to the preamplifier 6 as a self-diagnosis signal. The output signal is A
A / D conversion is performed by the / D converter 10, and the measured amplitude value is compared with the normal output amplitude value of the preamplifier 6 stored in the amplitude table 23 '. If this does not fall within the allowable error range, it is determined that the preamplifier 6 is out of order. The same applies to the diagnosis of the attenuator 9.

Diagnosis of Power Amplifier 7 It is assumed that the preamplifier 6 and the attenuator 9 have already been diagnosed and both are normal. The control circuit 2 'sets the switches 15 to 20 as shown in FIG.
By switching to dB, a self-diagnosis circuit is configured. First, the self-diagnosis signal is applied to the preamplifier 6 and then input to the power amplifier 7. After applying the output signal to the attenuator 9, the output signal is A / D converted by the A / D converter 10, and the measured amplitude value is stored in the amplitude table 23 ′. Compare with the amplitude value. If this does not fall within the allowable error range, it is determined that a failure has occurred. As described above, the diagnosis of each circuit constituting the high-frequency circuit section of the transmitter is performed.

[0015]

According to the present invention, a failure in a high-frequency circuit can be detected in a transmitter using a feedback system even when the transmitter is not transmitting.

[0016] Further, when the transmitter fails, it is possible to easily find the location of the failure.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of an overall configuration according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a Cartesian loop method according to the related art.

FIG. 3 is an explanatory diagram of a negative feedback circuit.

FIG. 4 is a diagram illustrating an example of states of switches 15 to 20.

[Explanation of symbols]

1: Output terminal, 2, 2 ': Control circuit, 3: Loop filter, 4: Quadrature modulator, 5: D / A converter, 6: Preamplifier, 7: Power amplifier, 8: Directional coupler, 9:
Attenuator, 10, 21: A / D converter, 11: Quadrature demodulator, 12: Adder, 13, 13 ': Main circuit, 14, 1
4 ': feedback circuit, 15-20: switch, 21: A / D converter, 22: oscillator, 23, 23': amplitude table, 2
6: Dummy load, 27: Baseband signal generation circuit,
28: Detection circuit,

Claims (3)

[Claims] 1. A Cartesian feedback type compensation circuit, etc.
In a linear modulation type transmitter for compensating for non-linear distortion caused by the amplitude or phase distortion of a power amplifier by a feedback circuit, a detection unit for detecting an amplitude value of an output of each circuit constituting a high-frequency circuit unit, and a transmitter By providing a self-diagnosis circuit for determining whether or not the high-frequency circuit unit to be configured is normal, and a control circuit for controlling the detection unit, the self-diagnosis circuit, and the entire transmitter, and performing a self-diagnosis before transmission. , Determine whether each circuit constituting the high-frequency circuit section is normal,
When a failure occurs, transmission is not performed. During transmission, the transmission output level is monitored. If the transmission output level becomes abnormal, transmission is stopped, a self-diagnosis is performed, and a failure point of the transmitter can be easily found. And the transmitter. 2. A Cartesian feedback type compensation circuit, etc.
A linear modulation type transmitter for compensating for non-linear distortion caused by amplitude or phase distortion of a power amplifier by a feedback circuit, wherein a baseband signal generating a baseband signal including two signals of an in-phase component and a quadrature component Circuit and
A D / A converter for D / A-converting the baseband signal, two adders to which in-phase component and quadrature component signals are input, and a signal for each of the in-phase component and quadrature component passing through the two adders, respectively And two loop filters, each of which inputs
A quadrature modulator for orthogonally modulating signals from two loop filters, an oscillator for providing a frequency for orthogonalizing the quadrature modulator, a preamplifier for amplifying a quadrature modulated signal output from the quadrature modulator, and the preamplifier A power amplifier that amplifies the output signal of the power amplifier, an output terminal that outputs the output signal of the power amplifier, a directional coupler that extracts a part of the output of the power amplifier, and a part that is extracted from the directional coupler. An attenuator for attenuating a signal; and a quadrature demodulator for demodulating an output signal of the attenuator. In a transmitter provided with a feedback circuit for compensating for nonlinear distortion of a power amplifier that is fed back, a dummy load connected to a power amplifier output during a self-diagnosis, and a directional coupler extracted A detection circuit for detecting the detected signal, an A / D converter for A / D converting the signal detected by the detection circuit, and an A / D converter for A / D converting the output signal of each circuit at the time of self-diagnosis. A changeover switch for switching between a normal transmission operation and a predetermined self-diagnosis operation; an amplitude table storing normal output amplitude values of each circuit constituting the high-frequency circuit portion; and an amplitude table for each circuit constituting the high-frequency circuit portion. Comparing the measured value with a normal value stored in the amplitude table, determining whether each high-frequency circuit is normal, and further comprising a control circuit for switching between a normal transmission operation and a self-diagnosis operation; The generation circuit generates a baseband signal during normal transmission, generates a self-diagnosis signal during self-diagnosis, and sets the gain of the loop filter to 0 dB during self-diagnosis according to a command from the control circuit. By performing self-diagnosis before transmission, the amplitude value of the output of the high-frequency circuit unit is detected, and it is determined whether or not each circuit constituting the high-frequency circuit unit is normal. Further, the transmitter monitors a transmission output level during transmission, does not perform transmission if the level is abnormal, performs self-diagnosis, and can easily find a failure point of the transmitter. 3. The transmitter according to claim 1, wherein a failure point of the transmitter is easily found by performing a self-diagnosis for individually checking the output amplitude of the high-frequency circuit. Transmitter.