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WO1992005631A1 - Method and arrangement for automatic gain control of a radio-frequency power amplifier - Google Patents

Method and arrangement for automatic gain control of a radio-frequency power amplifier Download PDF

Info

Publication number
WO1992005631A1
WO1992005631A1 PCT/FI1991/000292 FI9100292W WO9205631A1 WO 1992005631 A1 WO1992005631 A1 WO 1992005631A1 FI 9100292 W FI9100292 W FI 9100292W WO 9205631 A1 WO9205631 A1 WO 9205631A1
Authority
WO
WIPO (PCT)
Prior art keywords
radio
amplifier
signal
frequency
arrangement
Prior art date
Application number
PCT/FI1991/000292
Other languages
French (fr)
Inventor
Arto JÄNTTI
Original Assignee
Telenokia Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Telenokia Oy filed Critical Telenokia Oy
Publication of WO1992005631A1 publication Critical patent/WO1992005631A1/en

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3036—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers
    • H03G3/3042—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers in modulators, frequency-changers, transmitters or power amplifiers

Definitions

  • the invention relates to a method and an arrangement for automatic gain control of a radio- frequency power amplifier.
  • transmission-frequency signals from a modulator are usually amplified by a separate wide-band radio-frequency power amplifier before the signal is applied to an antenna.
  • the object of the invention is to provide gain control for a radio-frequency power amplifier, by means of which the magnitude of the output signal of even a non-linear amplifier can be adjusted to a desired level without a long control loop. This is achieved by means of a method according to the invention for the automatic gain ' control of a radio-frequency power amplifier, which method is characterized in that the gain of the amplifier is adjusted by a control signal obtained by comparing samples taken from the input and output signals of the amplifier.
  • the invention is also concerned with an arrangement for automatic gain control of a radio-fr ⁇ equency power amplifier, the arrangement comprising 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 comparing the sample signals with each other and for generating a control signal adjusting the gain of the radio-frequency amplifier on the basis of the comparison.
  • the invention is based on the idea that the gain of the amplifier is monitored and adjusted con ⁇ tinuously on the basis of sample signals taken from the input and output signals of the amplifier in such a way that the ratio between the input and output levels of the amplifier, i.e. the gain of the amplifier, is maintained constant.
  • the sampling of the input and output signals of the amplifier is preferably carried out by microstrip directional couplers or other similar means based on capacitive and/or inductive sampling, thus avoiding traditional measurement of gain by means of a series resistor measuring the collector current of the power transistor of the amplifier.
  • the preferred embodiment of the invention shown in the figure comprises a radio-frequency amplifier 1, preferably a non-linear radio-frequency power amplifier biased to operate in class AB, for instance.
  • the amplifier 1 comprises a radio-frequency signal input 10 to which a radio-frequency input signal RF IN to be amplified is applied e.g. from the transmitter itself when the amplifier 1 is a separate power amplifier, and a radio-frequency signal output 15 at which an amplified radio-frequency output signal RF OUT to be applied to a transmitting antenna is present.
  • the signal input 10 of the amplifier 1 comprises a microstrip directional coupler 2 which generates a sample signal 11 proportional to the magnitude or level of the incoming 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.
  • the signal output 15 of the amplifier 1 com ⁇ prises 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 super- vises the gain of the amplifier 1 by comparing the sample signals present at its inputs 13 and 14 with each other and/or with one or more predetermined reference values. On the basis of the comparison the comparator circuit 8 generates a power control signal 9 to be applied to the amplifier 1 so as to adjust the collector voltage of a power transistor forming a radio-frequency amplifier, stage in the amplifier 1 in order to maintain the total gain of the amplifier at a constant value.
  • the comparator 8 may also generate an alarm signal 16 when the magnitudes of the compared sample signals change in such a way that they meet a pre ⁇ determined alarm criterion.
  • the alarm criterion may be e.g. such that the alarm signal 16 is generated when the gain determined on the basis of the sample signals decreases below a predetermined reference value.
  • the sampling means 2 and 3 are advantageous to realize by a microstrip directional coupler due to the simplicity of such couplers and the high reproducibility offered by the microstrip technology.
  • the sample signals can be easily scaled already at the sampling stage for the comparison.
  • 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 by any suitable lowpass filtering technique.
  • 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.

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  • Amplifiers (AREA)

Abstract

The invention relates to a method and an arrangement for automatic gain control of a radio-frequency power 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 comparing the sample signals with each other and for generating a control signal (9) adjusting the gain of the radio-frequency amplifier (1) on the basis of the comparison.

Description

Method and arrangement for automatic gain control of a radio-frequency power amplifier
The invention relates to a method and an arrangement for automatic gain control of a radio- frequency power amplifier.
In radio transmitters, especially in multi¬ channel radio transmitters, transmission-frequency signals from a modulator are usually amplified by a separate wide-band radio-frequency power amplifier before the signal is applied to an antenna. The magnitude of the output signal of such a separate power amplifier should be the magnitude of the input signal multiplied by a certain constant, i.e. Pou-t*- = G x p in- This is achieved by using a linear amplifier. Linear amplifiers, however, operate in class A, so that their efficiency is low. In prior art arrangements, in order that the magnitude of the output signal of a non-liner power amplifier operating in class AB, for instance, would satisfy the above-mentioned condition, a feedback signal representing the output level of the separate power amplifier has been applied to a transmitter preceding the power amplifier, and the obtained closed loop has been used for adjusting the level of the output signal of the transmitter and thereby the power of the input signal to be applied to the separate power amplifier. In this way, however, the control loop may become long, so that the cable used in the feedback circuit gathers interferences from the surroundings and delays the operation of the loop (e.g. due to the capacitance of the cable). In addition, the trans¬ mitter may adjust itself to a maximum power level in case of a failure in the control loop. The object of the invention is to provide gain control for a radio-frequency power amplifier, by means of which the magnitude of the output signal of even a non-linear amplifier can be adjusted to a desired level without a long control loop. This is achieved by means of a method according to the invention for the automatic gain' control of a radio-frequency power amplifier, which method is characterized in that the gain of the amplifier is adjusted by a control signal obtained by comparing samples taken from the input and output signals of the amplifier.
The invention is also concerned with an arrangement for automatic gain control of a radio-fr¬ equency power amplifier, the arrangement comprising 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 comparing the sample signals with each other and for generating a control signal adjusting the gain of the radio-frequency amplifier on the basis of the comparison. The invention is based on the idea that the gain of the amplifier is monitored and adjusted con¬ tinuously on the basis of sample signals taken from the input and output signals of the amplifier in such a way that the ratio between the input and output levels of the amplifier, i.e. the gain of the amplifier, is maintained constant.
The sampling of the input and output signals of the amplifier is preferably carried out by microstrip directional couplers or other similar means based on capacitive and/or inductive sampling, thus avoiding traditional measurement of gain by means of a series resistor measuring the collector current of the power transistor of the amplifier.
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 a radio-frequency power amplifier having automatic gain control according to the invention.
The preferred embodiment of the invention shown in the figure comprises a radio-frequency amplifier 1, preferably a non-linear radio-frequency power amplifier biased to operate in class AB, for instance. The amplifier 1 comprises a radio-frequency signal input 10 to which a radio-frequency input signal RF IN to be amplified is applied e.g. from the transmitter itself when the amplifier 1 is a separate power amplifier, and a radio-frequency signal output 15 at which an amplified radio-frequency output signal RF OUT to be applied to a transmitting antenna is present. The signal input 10 of the amplifier 1 comprises a microstrip directional coupler 2 which generates a sample signal 11 proportional to the magnitude or level of the incoming 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. Correspond¬ ingly, the signal output 15 of the amplifier 1 com¬ prises 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 super- vises the gain of the amplifier 1 by comparing the sample signals present at its inputs 13 and 14 with each other and/or with one or more predetermined reference values. On the basis of the comparison the comparator circuit 8 generates a power control signal 9 to be applied to the amplifier 1 so as to adjust the collector voltage of a power transistor forming a radio-frequency amplifier, stage in the amplifier 1 in order to maintain the total gain of the amplifier at a constant value. The comparator 8 may also generate an alarm signal 16 when the magnitudes of the compared sample signals change in such a way that they meet a pre¬ determined alarm criterion. The alarm criterion may be e.g. such that the alarm signal 16 is generated when the gain determined on the basis of the sample signals decreases below a predetermined 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 by 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.
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 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 for automatic gain control of a radio-frequency power amplifier, c h a r a c t e r - i z e d in that the gain of the amplifier is adjusted by a control signal obtained by comparing 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 collector voltage of a power transistor forming a radio-frequency amplifier stage is adjusted by the control signal.
3. Arrangement for automatic gain control of a radio-frequency power amplifier (1), 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 comparing the sample signals with each other and for generating a control signal (9 ) adjusting the gain of the radio-frequency amplifier (1) on the basis of the comparison. •
4. Arrangement according to claim 3, 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 (10) and output (15) of the amplifier (1) in an inductive and/or capacitive manner.
5. Arrangement according to claim 4, 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.
6. Arrangement according to claim 4 or 5, c h a r a c t e r i z e d in that said means (8) for adjusting the gain comprise a differential amplifier having an output signal proportional to the difference between the sample signals applied to its inputs, which output signal generates said control signal.
PCT/FI1991/000292 1990-09-25 1991-09-23 Method and arrangement for automatic gain control of a radio-frequency power amplifier WO1992005631A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI904712A FI86350C (en) 1990-09-25 1990-09-25 Method and apparatus for automatic gain control in the high frequency amplifier
FI904712 1990-09-25

Publications (1)

Publication Number Publication Date
WO1992005631A1 true WO1992005631A1 (en) 1992-04-02

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI1991/000292 WO1992005631A1 (en) 1990-09-25 1991-09-23 Method and arrangement for automatic gain control of a radio-frequency power amplifier

Country Status (3)

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AU (1) AU8509391A (en)
FI (1) FI86350C (en)
WO (1) WO1992005631A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0632585A1 (en) * 1993-06-30 1995-01-04 Alcatel Telspace System for the bias control of an amplifier
EP0803973A1 (en) * 1996-04-25 1997-10-29 Lucent Technologies Inc. Linear power amplifier with automatic gate/base bias control for optimum efficiency
FR2810473A1 (en) * 2000-06-15 2001-12-21 Sagem DEVICE FOR PRODUCING A PHASE AND AMPLITUDE MODULATED RADIOELECTRIC SIGNAL AND METHOD FOR PRODUCING SUCH A SIGNAL
WO2006043140A1 (en) * 2004-10-22 2006-04-27 Nokia Siemens Networks Oy Method and apparatus for maintaining constant linearity for a power amplifier over varying load conditions

Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2213099A (en) * 1935-12-11 1940-08-27 Rediffusion Ltd Distortion indicator for electrical amplifying systems
US3495179A (en) * 1966-06-23 1970-02-10 Hewlett Packard Co Amplifier overload indicator
US3833856A (en) * 1973-11-15 1974-09-03 Us Navy Apparatus for testing an amplifier
US4032853A (en) * 1976-10-28 1977-06-28 Hibbs Jr Eugene B Overdrive detector for radio frequency amplifier
US4048573A (en) * 1976-10-15 1977-09-13 Mcintosh Laboratory, Incorporated Amplifier improvements for limiting clipping
GB2081038A (en) * 1980-07-25 1982-02-10 Inst Francais Du Petrole Devices for amplifying and sampling multiplexed signals
EP0078130A2 (en) * 1981-10-28 1983-05-04 Cbs Inc Automatic loudness controller
EP0171843A2 (en) * 1984-08-17 1986-02-19 Philips Electronics Uk Limited Bipolar transistor RF power amplifier
US4574248A (en) * 1984-05-07 1986-03-04 Rockwell International Corporation RF Power amplifier for use with VHF transceivers
WO1987004305A1 (en) * 1985-12-30 1987-07-16 Hughes Aircraft Company Traveling wave tube drive controller
US4694258A (en) * 1986-03-14 1987-09-15 General Instrument Corporation Method and system of enhancing performance of feedforward amplifiers
EP0238286A2 (en) * 1986-03-18 1987-09-23 Nec Corporation Automatic gain control apparatus

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2213099A (en) * 1935-12-11 1940-08-27 Rediffusion Ltd Distortion indicator for electrical amplifying systems
US3495179A (en) * 1966-06-23 1970-02-10 Hewlett Packard Co Amplifier overload indicator
US3833856A (en) * 1973-11-15 1974-09-03 Us Navy Apparatus for testing an amplifier
US4048573A (en) * 1976-10-15 1977-09-13 Mcintosh Laboratory, Incorporated Amplifier improvements for limiting clipping
US4032853A (en) * 1976-10-28 1977-06-28 Hibbs Jr Eugene B Overdrive detector for radio frequency amplifier
GB2081038A (en) * 1980-07-25 1982-02-10 Inst Francais Du Petrole Devices for amplifying and sampling multiplexed signals
EP0078130A2 (en) * 1981-10-28 1983-05-04 Cbs Inc Automatic loudness controller
US4574248A (en) * 1984-05-07 1986-03-04 Rockwell International Corporation RF Power amplifier for use with VHF transceivers
EP0171843A2 (en) * 1984-08-17 1986-02-19 Philips Electronics Uk Limited Bipolar transistor RF power amplifier
WO1987004305A1 (en) * 1985-12-30 1987-07-16 Hughes Aircraft Company Traveling wave tube drive controller
US4694258A (en) * 1986-03-14 1987-09-15 General Instrument Corporation Method and system of enhancing performance of feedforward amplifiers
EP0238286A2 (en) * 1986-03-18 1987-09-23 Nec Corporation Automatic gain control apparatus

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0632585A1 (en) * 1993-06-30 1995-01-04 Alcatel Telspace System for the bias control of an amplifier
FR2708399A1 (en) * 1993-06-30 1995-02-03 Alcatel Telspace Amplifier polarization control system.
US5430410A (en) * 1993-06-30 1995-07-04 Alcatel N.V. Amplifier bias control system
EP0803973A1 (en) * 1996-04-25 1997-10-29 Lucent Technologies Inc. Linear power amplifier with automatic gate/base bias control for optimum efficiency
FR2810473A1 (en) * 2000-06-15 2001-12-21 Sagem DEVICE FOR PRODUCING A PHASE AND AMPLITUDE MODULATED RADIOELECTRIC SIGNAL AND METHOD FOR PRODUCING SUCH A SIGNAL
WO2006043140A1 (en) * 2004-10-22 2006-04-27 Nokia Siemens Networks Oy Method and apparatus for maintaining constant linearity for a power amplifier over varying load conditions
US7190221B2 (en) 2004-10-22 2007-03-13 Nokia Corporation Method and apparatus for maintaining constant linearity for a power amplifier over varying load conditions

Also Published As

Publication number Publication date
FI904712A0 (en) 1990-09-25
FI86350C (en) 1992-08-10
AU8509391A (en) 1992-04-15
FI904712A7 (en) 1992-03-26
FI86350B (en) 1992-04-30

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