WO1992005630A1

WO1992005630A1 - Method and arrangement for supervising the condition of a radio-frequency amplifier

Info

Publication number: WO1992005630A1
Application number: PCT/FI1991/000291
Authority: WO
Inventors: Esko Prokkola
Original assignee: Telenokia Oy
Priority date: 1990-09-25
Filing date: 1991-09-23
Publication date: 1992-04-02
Also published as: AU8516591A; FI904711A; FI904711A0; FI85784C; FI85784B

Abstract

The invention relates to a method and an arrangement for supervising the condition of a radio-frequency amplifier. The arrangement of the invention comprises a first sampling means (2) for generating a sample signal (11) from the input signal of the radio-frequency amplifier (1); a second sampling means (3) for generating a sample signal (12) from the output signal of the radio-frequency amplifier (1); and means (8) for monitoring the gain of the radio-frequency amplifier (1) on the basis of the sample signals.

Description

Method and arrangement for supervising the condition of a radio-frequency amplifier

The invention relates to a method and an arrangement for supervising the condition of a radio- frequency amplifier.

In radio transmitters, especially multi-channel radio transmitters, transmission-frequency signals from a modulator are usually amplified by a separate wide-band radio-frequency power amplifier. It is thereby important that the condition and especially the gain of the RF power amplifier can be monitored so as to obtain information about a failure in the RF power amplifier. On the basis of such information, the level of the signal to be applied to the RF power amplifier from preceding amplifier stages can be in¬ creased or decreased, for instance.

Typically, the supervision of the condition of an RF amplifier has based on the measurement of the collector current of the power transistor of the amplifier by means of a series resistor having a low resistance. A problem therewith is that it is necessary to use a high-power resistor and perform a floating voltage measurement across this resistor. The object of the invention is to provide a novel method and arrangement for supervising the condition of a radio-frequency power amplifier.

This is achieved by means of a method of the invention which is characterized in that the gain of the amplifier is monitored on the basis of samples taken from the input and output signals of the amplifier.

The object is also achieved by means of an arrangement according to the invention, which is characterized in that it comprises a first sampling means for generating a sample signal from the input signal of the radio-frequency amplifier; a second sampling, means for generating a sample signal from the output signal of the radio-frequency amplifier; and means for monitoring the gain of the radio-fre¬ quency amplifier on the basis of said sample signals.

In the invention, sample signals are taken from the RF input signal and the amplified RF output signal of the RF amplifier. The sample signal obtained from the output of the amplifier is propor¬ tional to the gain of the amplifier, so that the gain of the amplifier and thus its condition can be measured by means of the sample signals by comparing the sample signals with each other or with a refer- ence value. The condition supervision according to the invention by means of sampling does not require high-power resistors and the measuring arrangement is simple and easy to realize. In addition, the measuring arrangements are small in size, as the sampling can be realized by a printed circuit board utilizing microstrip directional couplers, whereby the scaling can be carried out already at the sampling stage.

The invention will now be described in greater detail by means of an embodiment with reference to the attached figure, which shows a block diagram of an arrangement according to the invention for supervising the condition of a radio-frequency amplifier. The preferred embodiment of the invention shown in Figure 1 comprises a radio-frequency amplifier 1, preferably a radio-frequency power amplifier, which operates e.g. in class AB. The amplifier 1 is additionally coupled to an operating voltage ^+v _cc. The amplifier 1 comprises a radio-frequency signal input 17 to which a radio-frequency input signal RF IN to be amplified is applied, and a radio-frequency signal output 18 at which an amplified output signal RF OUT is present. The signal input 17 of the amplifier 1 comprises a microstrip directional coupler 2 which generates a sample signal 11 proportional to the magnitude or level of the in¬ coming signal, which sample signal is detected by a detector circuit 4 and filtered by a lowpass filter 5 before it is applied to an input 13 in a comparator circuit 8. Correspondingly, the signal output 18 of the amplifier 1 comprises a microstrip directional coupler 3 which generates from the output signal of the amplifier a sample signal 12 proportional to the magnitude or level of the output signal, and the sample signal is detected by a detector circuit 6 and filtered by a lowpass filter 7 before it is applied to another input 14 in the comparator 8. The comparator 8 supervises the gain of the amplifier 1 by comparing the sample signals present at the inputs 13 and 14 with each other and/or with one or more predetermined reference values. The comparator 8 generates an alarm signal ALARM when the magnitudes of the compared sample signals change in such a way that they meet a predetermined alarm criterion. The alarm criterion may be e.g. such that the alarm signal ALARM is generated when the magnitude of the sample signal taken from the output signal decreases while the magnitude of the sample signal taken from the input signal remains constant, that is, when the gain of the amplifier decreases. An alarm signal can be generated also when the gain determined on the basis of the sample signals decreases below a pre¬ determined reference value. It is advantageous to realize the sampling means 2 and 3 by a microstrip directional coupler due to the simplicity of such couplers and the high reproducibility offered by the microstrip technology. By suitable dimensioning of the directional coupler, the sample signals can be easily scaled already at the sampling stage for the comparison. However, the sampling means may be realized by any other directional coupler or other similar device effecting an inductive and/or capacitive coupling, such as a separate pick-up thread or pick-up capacitor.

The detecting means 4 and 6 effecting the power detection are preferably half-wave rectifiers effected by means of a diode, and the filters 5 and 7 can be realized with any suitable lowpass filtering technique. At simplest, the comparator circuit 8 can be realized by an operational amplifier coupled as a differential amplifier, which compares the signals present at the inputs 13 and 14 with each other, thus giving directly an output control signal proportional to the gain. The output of the differential amplifier may further comprise a comparator circuit for comparing the level of the output signal of the differential amplifier with one or more reference values and for generating the alarm signal ALARM when the predetermined alarm criterion is met.

Some or all of the above-described functions can also be realized digitally, which, however, may result in a more complicated and more expensive structure. The alarm signals generated by the comparator 8 can be applied to any unit monitoring and controlling the operation of the radio transmitter or amplifier.

The attached figure and the description related to it are only intended to illustrate the present invention. In their details, the method and the arrangement according to the invention may vary within the scope of the accompanying claims.

Claims

Claims:

1. Method of supervising the condition of a radio-frequency amplifier, c h a r a c t e r i z e d in that the gain of the amplifier is monitored on the basis of samples taken from the input and output signals of the amplifier.

2. Method according to claim 1, c h a r a c ¬ t e r i z e d in that the gain is monitored by comparing the input signal sample and the output signal sample with each other.

3. Method according - to claim 1, c h a r a c ¬ t e r i z e d in that the gain is monitored by comparing the input signal sample and the output signal sample with one or more predetermined reference values.

4. Method according to claim 1, 2 or 3, c h a r a c t e r i z e d in that the samples are scaled before the comparison.

5. Method according to any of the preceding claims, c h a r a c t e r i z e d in that an alarm signal is generated when the gain decreases while the input signal level remains constant.

6. Method according to any of the preceding claims, c h a r a c t e r i z e d in that an alarm signa is generated when the gain decreases below a predetermined reference value.

7. Arrangement for supervising the condition of a radio-frequency amplifier, c h a r a c t e r - i z e d in that the arrangement comprises a first sampling means (2) for generating a sample signal (11) from the input signal of the radio-frequency amplifier (1); a second sampling means (3) for generating a sample signal (12) from the output signal of the radio-frequency amplifier (1); and means (8) for monitoring the gain of the radio- frequency amplifier (1) on the basis of said sample signals.

8. Arrangement according to claim 7, c h a r ¬ a c t e r i z e d in that said sampling means (2, 3) are coupled to the input (17) and output (18) of the amplifier (1) in an inductive and/or capacitive manner.

9. Arrangement according to claim 8, c h a r ¬ a c t e r i z e d in that said first and second sampling means (2, 3) are formed by directional couplers, preferably microstrip directional couplers.