Method and apparatus for adaptively controlling the gain of an amplifier

The invention relates to an apparatus for regulated amplification of digital signals, in particular for a digital broadcasting system according to claim 1 and a A method for adaptively controlling the gain of a Amplifying device according to claim fourteenth

More recently, digital terrestrial Rundfunksyteme such. B.The DAB (Digital Audio Broadcasting) -T- or DVB (Digital Video Broadcasting) -T system, operated in single frequency networks, where by Sending multiple locations in sync. to fill coverage gaps repeater amplifiers are used, the transmission and reception antennas due to a Radiation coupling are fed back. If the gain a repeater amplifier decoupling attenuation between the transmitting and receiving antenna is reached, this device in Vibration. To oscillations and thus an unstable To avoid operation, the gain to a must Safety distance be less than the Decoupling attenuation. understood under the safety distance you generally measured in dB difference between the decoupling attenuation between the input and output of a Amplifier and its amplification factor. Since the Radiation coupling between the transmitting and receiving antenna the repeater amplifier by environmental influences such. B. by flying in front of an antenna assets (aircraft, birds, Snow, etc.) or by temporarily on the antenna contained objects can be time-variant, the Decoupling attenuation temporarily be reduced such that the repeater amplifier starts to vibrate. to a To ensure stable operation, are previously known, controlled amplifier or repeater amplifiers such designed such that the gain static one substantial safety margin, for example, by 15 dB, under a measured average decoupling attenuation is set. The mean decoupling damping results essentially of systemic characteristics such as for example, the orientation of the transmitting and receiving antenna, the Spacing of the antennas to each other and offset in height Mounting the transmitting and receiving antennas. Although in the known repeaters the safety distance quite large is selected, it can nevertheless self-excitation of the Repeater amplifier come when the Decoupling attenuation temporarily or permanently drastically reduced. A reduction of the safety margin occurs also, when the signal level at the repeater output decreases, because then, in the conventional output power control of the Gain rises to the drop in output counteract. In the conventional repeater amplifiers, their gain regardless of the current Decoupling attenuation is adjusted, it is also very difficult to determine whether the safety distance with respect the swing cutoff point with too much of a reserve has been set, and thereby supply range and quality is presented, whereby the repeater operated uneconomical.

The invention is therefore based on the object, the mentioned amplifier further such that this economically efficient than before can be operated.

This technical problem the invention solves each with the features of claim 1 and Method steps of claim 14.

The invention takes into account the fact that digital communication systems powerful Error detection and error correction process for Apply avoid interference. That's why it is quite tolerable, that an amplifier over a short Period of, for example, a few microseconds with poor quality or even with a Interruption of transmission are operated unstable can without a listener or viewer aware of this.

The core idea of ​​the invention is the fact that by repeated kurzeitiges upsampling the gain it is checked whether the gain for a stable operation the amplifier can be increased or decreased must become. In this way it is achieved that the Amplifier most of the time with the greatest possible Gain can be operated, whereby both the Supply range and the quality of care be improved over known static amplifiers can.

This is achieved by the invention by a device for the regulated amplification of digital signals, in particular for a digital broadcasting system, with a Signal input and a signal output, said apparatus a preset gain (V₀) Returns. Further, a means for increasing the preset Gain (V₀) By a first predetermined amount in predetermined time intervals for in each case a predetermined period of time as well as a monitoring and Evaluating means for monitoring and evaluating the Operating state of the device at least in the predetermined time intervals is provided. In Dependence of the output signal of the monitoring and Evaluation carried out an increase or a Reduction of the preset amplification by a second predetermined amount. For example, the first predetermined amount of 9 dB and the second predetermined Amount 0.5 dB. corresponds to the first predetermined amount thereby the desired maximum difference, even called safe distance, between an average Decoupling attenuation between the input and the output the amplifier and its gain.

According to an advantageous embodiment, the Device comprises a first variable gain amplifier for delivery the preset gain, whereby the device for repeated temporary increasing the gain a second variable gain amplifier, a clock and connected one to the second variable gain amplifier having Tastimpulsformer. The clock and the Tastimpulsformer place while the recurring Window fixed, within which the preset increased gain and the operating state of the Amplifier is checked. The output of Tastimpulsformers therefore is a pulse train having a through the clock predetermined repetition rate, the Pulses, an adjustable pulse width, for example 40 possess microseconds. The amplitude of the of the Tastimpulsformer formed pulses is selected such that they for the Increasing the preset amplification by the first predetermined amount provides. Advantageously, selects the Tastimpulsformer in communication with the clock, the Time points and duration of the gain increase such that on the one hand disturbances during the gain increase are generated because of the error protection in the recipient is not are perceptible in the amplifier and on the other hand the can be recovered and processed information that the predetermined safety distance beyond the duration of the Gain increase is observed.

Already at this point it should be mentioned that in order to Optimizing the adaptive control of the gain on the Signal output signal present may be used, the clock frequency of the clock and / or the pulse duration of the of the Tastimpulsformer changing pulses generated. For example, the clock is an output activated when the level exceeds a pre-set, exceeds system optimized level.

To increase or decrease the preset gain is a gain controller provided, the input side to the Clock and the monitoring and evaluation and its output connected to the first amplifier is. increases the gain control device or decreases the gain of the first amplifier For example, in intervals of 0.5 dB. However, the Amplification swing set.

The device of the invention can advantageously be in a regulated repeater for digital radio systems, such as for example, are used in the DAB-T and DVB-T systems. Such a repeater usually has an output stage and a band pass filter on the signal output. The bandpass filter has the task of spurious emissions that are Signal frequencies outside the predetermined Frequency range to suppress. In the inventive Amplifier has the bandpass filter is further operable to prevent the amplifier outside the Transfer belt vibrates while it is allowed to he momentarily during the duration of the gain increase within the radio service assigned transmission band swings. In addition, the repeater is equipped with a se known level indicator provided on the input side with the signal output and on the output side to the amplification control means is connected to the preset to increase gain by a predetermined amount when the signal power at the signal output to the preset, system optimized power level falls below. Optimized system power level is here that the level the output signal for supplying a predetermined Area is sufficient.

Advantageously, the gain control means connected to the clock pulse shaper and generated in response to these different Amplifier control signals. In this way, it is possible that the gain controller, the gain the first amplifier by a larger step decreased, when a deterioration of the Operating state of the amplifier outside the repeated, temporary gain increase is detected.

In the to be monitored and evaluated Operating state is advantageously a possible oscillation state of the device. That is, the Monitoring and evaluation first monitors Device to determine whether it resonates or not. If a Vibration detected, the preset gain the first amplifier is reduced. In this case it is at the monitoring and evaluation by a Vibration detector.

According to a further embodiment of the monitoring and Evaluation, an unstable operating condition the device will be determined by the fact that the Change in current consumption of the device when this from Operation of the stable gain in the unstable operation the vibrational transitions, which increased power output, the increased occurrence of harmonics due to a Clipping or the crossing of Linearity limit or the reduction or Disappearance of level variations in the amplified signal is evaluated.

Alternatively or additionally, the monitoring and Evaluation be designed such that they the monitored bit error rate of the received digital signal, and compares it with a predetermined value. Another alternative embodiment of the monitoring and Evaluation is that the ripple of the Transfer function is analyzed in the frequency domain. The Exceeding a predetermined value allows systemic be defined threshold of degradation the signal transmission can be seen. Waviness Transfer function of the apparatus arises in that by feedback from a frequency independent a frequency-dependent transfer function. Where that the ripple of the transfer function is greater, the smaller the margin of safety for use of the swing Device. Another development of the monitoring and Evaluation allows monitoring and Evaluation of modulation induced level fluctuations in amplified signal in the frequency domain. As an example of an OFDM signal in DAB-T-Sytemen intended. In this case a degradation of the transmission signal is detected if drop the level variations below a predetermined value or disappear completely substantially. With these Criteria and using appropriately adjusted Reference values, it is possible to transition the device in an unstable state before the onset of Vibrations to be recognized.

According to an advantageous development, the Output of the device arranged an amplitude be, which is only activated by the timer, if the gain is increased by said first amount.

Advantageous developments are the subject of Subclaims.

With the aid of the inventive device and of the Method of the invention it is possible, outside of recurring short periods of time in which the gain is raised, a predetermined, comply with minimum safety distance at which the Device can still be operated sufficiently stable.

The invention will be described by way of Embodiment in conjunction with the accompanying Drawings explained in more detail. Therein:<dl tsize="7" compact="compact"><dt>Fig. 1</dt><dd>a block diagram of an adaptive repeater with a resonant application monitoring,</dd><dt>FIG. 2</dt><dd>a gain-time diagram of the regulated Amplification of the controllable amplifier,</dd><dt>Fig. 3</dt><dd>Time diagram of an exemplary pulse sequence which from the shown in Fig. 1 for Tastimpulsformer Control of the stepwise variable gain amplifier is generated, and</dd><dt>Fig. 4</dt><dd>a gain-time diagram of the overall gain of the adaptive repeater according to the invention according to FIG. 1.</dd></dl>

FIG. 1 shows the basic circuit of an adaptive Repeater for example in a digital terrestrial broadcasting system to refresh digital is usable signals. is already at this point mentioned that the device according to the invention not only in the repeater described below, but also in other amplifiers in which the output to the input coupled, are applicable. The generally at 10 Marked adaptive repeater comprises a signal input 15, to which a receiving antenna is connected 17th The Receiving antenna 17 is connected to a controllable amplifier 20 connected, which is known per se. In per se known Way includes the repeater 10 Next as Power Amplifier Output Stage Circuitry 40, a Bandpass filter 50, a signal output 60 and a thereto on connected transmission antenna 65. Typically a Level indicator 70 on the input side to the signal output 60 connected, the output of which is known per se via a Gain control means 80 with the controllable Amplifier 20 is connected. As essential to the invention Component comprises the repeater 10, an adaptive Amplifier stage 100. The adaptive gain stage comprises 100 a stepwise variable gain amplifier 30, the input side to the controllable amplifier 20 and whose output is connected to the output stage 40th About that addition, the adaptive gain stage 100 a Clock 85 on the input side to the signal output 40 may be connected. A monitoring and Evaluation 90 is, for example, to the output of the output stage 40, as the operating state when the Schwing use of the repeater 10 is monitored. About that addition, the output of the monitoring and Evaluating device 90 with an input of a Tastimpulsformers 110. The Tastimpulsformer 110 whose output is in turn connected to the stepwise variable Amplifier 30 and the gain control means 80 connected. The monitoring and evaluation 90 further comprising an input of the gain control means 80 and optionally with an input the clock 85 connected. The clock 85 can both to an input of Tastimpulsformers 110 as well as with an input of the gain control means 80 be connected. The output of the clock 85 can turn with the input of the level indicator 70 and an input of the Monitoring and evaluation to be 90 connected.

The operation of the adaptive repeater 10 more detail below in connection with Figs. 2 to 4 explained. It is assumed that the adaptive repeaters 10 following preset sizes System has:<sl><li>a) amounts to the gain of the variable gain amplifier 20 V₀; the reinforcement is chosen such that a predetermined area can be fully supplied;</li><li>b) the safety distance, ie the difference between an average shopping decoupling attenuation between the transmitting antenna 65 and the receiving antenna 17 of the adaptive repeater 10 and the optimized reinforcing V_O the repeater 10 amounts to 9 dB,</li><li>c) amounts to the period of the clock signal from the clock 85 0.5 s,</li><li>d) have the pulses generated by Tastimpulsformer 110 a pulse width of 40 microseconds and cause an increase the gain of the stepwise variable gain amplifier 30 by 9 dB effected.</li></sl>

The effect thus selected system variables that the adaptive repeater 10 starts to vibrate when its Gain by about 9 dB is raised or the Decoupling damping deteriorates by about 9 dB. It should further assumed that the monitoring and Evaluation device 90 in the present example, as Vibration detector is formed which detects when the adaptive repeater 10 goes into the vibrational state.

It is assumed that the adaptive repeaters 10 initially is in a stable operating state, wherein the gain of the variable gain amplifier 20 at the time T = 0 V₀ is. Further, the repeater 10 is such designed so that the vibration detector 90 during the total operating time is activated. At time t₀generated as shown in Fig. 3, the clock 85 a Clock pulse 110 to produce a the Tastimpulsformer Activated pulse with a duration of 40 microseconds. This pulse is the stepwise variable gain amplifier 30 is supplied, the in response thereto, the gain of the repeater 10 to 9 dB increases. The overall gain, as in Fig. 4 Curve 2 is shown, therefore, is at time t₀ V₀ + 9 dB, which corresponds to the average damping decoupling. In Practically, the average damping decoupling somewhat be higher than the raised overall gain to a Swinging the repeater 10 during an increase in the To avoid amplification of the controllable amplifier 20 then, when the average gain is not lowered. Of the time course of the decoupling damping is in Fig. 4 as Curve 1 shown. As shown in Fig. 4, the Decoupling damping during the time duration of the first Pulse 3, for example because of a passing Vogels, fallen off, so that the overall gain of the adaptive repeater 10 is greater than the decoupling attenuation is. The vibration detector 90 notes, therefore, that the Repeater 10 swings. Since the input of the gain control means 80 of the first pulse of 3 Tastimpulsformers 110 bears, recognizes the adaptive Amplifier stage 100 is that the repeater 10 during the periodic raising the gain V_O the repeater 10 in Vibration is advised. The adaptive gain stage 100 is implemented such that the gain of the stages variable gain amplifier 30 immediately after discovery of the Schwing use of the repeater 10 is reduced to zero and at the same time the gain V₀ the repeater 10 via the Gain control means 80 by a predetermined small amount, for example, by 0.5 dB, reducing, as shown in Fig. 4. The operating gain the repeater 10 is now V₀ - 0.5 dB. Although the repeater 10 is now working with a reduced gain, but the preset Safety distance, the stable operation ensures essentially retained. As shown in Fig. 4, the attenuation increases after the decoupling brief drop back to a normal level, so that the vibration detector 90 initially not Vibration use longer detected. After a period of 0.5 s generates the clock an additional clock pulse to the Tastimpulsformer 110 and the vibration detector 90 is supplied to signal that the periodic Examination of the oscillation behavior of the repeater 10 again starts. The Tastimpulsformer 110 generates a second 4 pulse with a duration of 40 microns, again raising the the gain of the stepwise variable Verstäkers 30 and thus causing the overall gain of the repeater to 9 dB. The overall gain shown in Fig. 4 is, for time t₁ thus V₀ + 9 dB - 0.5 dB. Since the Decoupling attenuation between the receiving antenna 17 and the Transmit antenna 65 is greater than the total gain of the Repeater 10, the vibration detector 90 no Waving firmly. After 40 microseconds the gain is reduces the stepwise variable gain amplifier 30 to 0 dB and at the same time the gain of the variable gain amplifier 20 is raised by 0.5 dB as shown in Fig. 2.

As shown in Fig. 4, now falls outside the cyclical monitoring of the oscillation behavior of the Repeater 10, ie, between the second and third Clock pulse, the decoupling attenuation z. B. by a close flying by metallic aircraft such drastically from that of the repeater unit 10 to vibrate. Of the Vibration detector 90 detects the swing state of Repeater 10 and the fact that no polling the repeater 10 is present, since it from clock 85 no Clock pulse received. The vibration detector 90 signals the vibration using the repeater 10 to the Clock 85, of the then a clock pulse Level indicator 70 and to gain controller 80 transfers. Since the oscillation of the repeater 10 outside cyclical monitoring has occurred, generates Gain control means 80 a control signal indicative of the Amplification of the controllable amplifier 20 drastically reduced, so that the repeater 10, although with a very weak amplification is operated, but the Operating condition is stable. The by the clock 85 activated level indicator 70 determines that the Signal level at the signal output 60 is now below the optimized, preset signal level is. to Introduction of the cyclical monitoring of the Vibration behavior of the repeater 10 generates the clock 85 again, a clock signal both to the oscillation detector 90, the level indicator 70, the 110 and the Tastimpulsformer Gain control means 80 is supplied. at Although the example described here is the clock signal for Controlling the periodic monitoring of Vibrational state of the repeater 10 irrespective of the Power loss at the signal output 60. It is conceivable, however, the clock generator 85 in response to the signal level at the Output 60 of the repeater 10 to control. The clock 85 then generates a clock signal, the premature cyclical Monitoring of the repeater 10 in its wake. We return now to the exemplary scenario back. Of the Tastimpulsformer 110 subsequently produced a third 5 pulse, which causes the gain of the stages variable gain amplifier 30 is raised by 9 dB. There now the decoupling damping a higher value than the mean damping decoupling adopted because z. B. the previously flying past metallic aircraft itself has a far cry from the repeater 10, occurs during cyclical monitoring to no vibration behavior. Of the Vibration detector 90 then causes the gain controller 80, the gain of the variable Amplifier 20 to raise a small amount of 0.5 dB. but it is also possible that in response to the Level indicator 70, which at the distinct change in performance Signal output has detected 60, the gain of the variable Amplifier 20 to a larger Bertrag, for example, 1 dB is raised. This is illustrated in Fig. 2 and 4. Furthermore, the level indicator can 70 with the clock 85 be connected, then the period of the clock signal changed depending on the output power. For example, the period is shortened when the Level indicator 70 a predetermined power drop at Signal output 60 is detected. In this way, the Gain of the repeater 10 is rushed to brought preset optimum gain value will. Thanks to the invention it is therefore possible to Repeater 10 almost throughout the operating time with the to allow maximum possible gain work, the preset safety distance substantially maintained becomes.

In order during cyclical monitoring or raising the overall gain to 9 dB, the output signal amplitude-limiting, can amplitudenbegrenzende Devices can be provided, which are not shown. Such limiter circuits are generally known. Of the Skilled can, however, also with diode limiter from clock 85 controlled or bias Limiter with by the clock signal of the clock 85 switchable limiter threshold or assemblies Amplifier stages with fixed and Limiter subsequent switchable attenuators - in connection with a counter to their weakening magnification the gain increase in stepwise variable Amplifier 30 - choose.

In principle, for the repeater according to the invention the same procedure will be described, when in Fig. 4, the Curve 1 does not use the oscillation but a measure of the represents quality of the transmission signal of the amplifier, which results from the bit error rate or from the ripple of the Transfer function in the frequency domain results. The Strobe pulses 3, 4, 5, ... then solve each of the query meanwhile in the monitoring and Evaluation determined bit error rate or Ripple from.

The circuit arrangement shown in FIG. 1 of adaptive repeater can at least partially or completely as a low cost integrated circuit in a be summarized common function.