# Patent

## Title
Control of data transmission voltage level using clipping in a low-voltage network

## Abstract

A method is provided for controlling a load signal of a signal transmitter in a data system for sending data in a low voltage network in order to keep an input signal voltage constant. The load signal is supplied through a coupling unit that provides signal coupling the network. The data transmission system also includes a signal amplifier, a signal filter and a source of signal amplifier operating voltage. The signal amplifier includes a signal clipper or a function for clipping the output signal of the signal amplifier and/or for clipping the input signal amplifier. The clipping is dependent on the output voltage of the signal to be sent to the network or on the output current from signal amplifier.

## Background
BACKGROUND OF THE INVENTION
The invention is suited for control of the voltage level of load signals UL from transmitters in a data transmitting system sending data in low-voltage network. The aim is to keep the load signal as to its voltage level as constant as possible in the transmitter mains connection that is independent of net impedance, which impedance can sometimes be quite low and thus tending to attenuate the load signal to a degree unfit for use with respect to reliable communication. Usually, by low-voltage a net of 230 V 50 Hz or some other low-voltage net is referred to.
CROSS-REFERENCE TO RELATED APPLICATIONS
In quite traditional systems the voltage amplitude of the load signal drops strongly, when the impedance is attenuating. The maximum output level (EUROPE) can drop from 122 dBu V even to 16 dBu V (1⁄6 voltage level) the net impedance then being 1 ohm. Mostly even this kind of systems can work reliably most of the time, but the fact that they are not always working correctly, make them, commercially thinking, unusable. FIG. 1 shows a prior art solution.
In my opinion the most advanced modern techniques is in this respect represented by PCT application WO 01/15334 A1 (Aug. 17, 2000). In it the load signal is kept almost constant in the transmitter mains connection by means of feedback coupling independent of net impedance and frequency. The method is based on the fact that the current feed capacity of the signal amplifier to a network of 230 V 50 Hz working as load is increased the more the lower the network impedance ZL is. The above presented is a system, where in my opinion the signal (sinus shaped) is by no means cut from its peaks, but the signal amplifier pushes the more sinus shaped power to load ZL the lower the ZL is by each frequency. Thus load signal UL across ZL remains almost constant. However, no curve UL=UL(ZL) is presented so there is no knowledge of the load signal level, for instance by low ZL values and also no knowledge of the quality of the invention.
The disadvantage of the feedback coupling system is, however, possible susceptibility against many kinds of disturbances appearing in the network if no interference suppression has been carried out most effectively. Also in EMC (“electromagnetic compatibility”) tests the transmitters do not pass easily without good EMC characteristics. Effective suppression against interference increases the manufacturing costs of transmitters a little. In this case situation is weakened because feedback signals UM and 1M×RCS=Umass are taken directly from points easily reached by disturbances from a network without suppression. If interference is carried out correctly and properly working, the method disclosed in the
respective PCT publication is good.
BRIEF SUMMARY OF THE INVENTION
In the present invention the amplitude of the signal is controlled by clipping and/or distorting of the signal, rather than by gain control of the signal amplifier without clipping or distorting of the signal. ACC=Automatic Cutting Control. The aim of this invention is to keep also load signal UL constant in net impedance ZL, in other words independent net impedance ZL, but in quite another way, that is by cutting the output voltage of the signal amplifier from its peak, or in another way by cutting or distorting when ZL is high and load voltage UL would without cutting tend to be too high. Alternatively cutting can be carried out by reducing the supply voltage of the signal amplifier so that cutting takes place already in the signal amplifier. After cutting, the low pass filter and bandpass filter filter off harmonic waves generated on cutting under maximum level as required by standard. The method as per this invention is characterized in what is presented in the claims.
If the net impedance is low enough no signal cutting takes place but the maximum signal of signal amplifier is fed forward and further as such to the network. Thus a load voltage UL, remaining constant, is achieved also with low net impedance values.
The input voltage UIN of the signal amplifier is of constant amplitude as also the output voltage UOUT of the signal amplifier (signal amplifier supply voltage US is constant, in other words ungovernable). This holds true for the above presented text.
Described above is that cutting of output signal can take place in signal amplifier or after it by cutting it from its peak. Another alternative is that the output signal is cut in the signal amplifier or in subsequent blocks or in some other way. One possibility is ‘zero point cutting’, with other words the signal is cut from the centre so that positive and negative half periods can pass through as far their peaks are concerned, but from the root always a part of the half period is omitted. There are also other possible ways of cutting. If it is the question of a sinusoidal signal, the signal gets distorted on cutting and generated harmonic waves must be filtered off before getting fed into the network. Also such a method can be used that the input signal UIN of signal amplifier is cut from line impedance ZL by a dependent way. E.g. UL is applied to Control Unit 60 and UACC or IACC is fed to Signal Amplifier 20 to clip and/or distort UIN.
The control of load signal UL is in this invention always based on cutting the signal in one way or another. So it is not the question that the signal amplitude is controlled, while the signal is however retaining its original shape. It is quite another way of signal control (ALC and AGC), with other words automatic level control and automatic gain control.
ALC=Automatic Level Control
AGC=Automatic Gain Control
In this invention keeping the voltage level of load signal UL constant by the cutting principle takes place so that the transmitter sends a signal in principle at maximum level to the network, but the signal tending to grow by high ZL values is restricted in early blocks by cutting or distorting.
The cutting system has no impact on power consumption, since source voltage (US) must be dimensioned according to the situation of maximum load. Maximum power consumption appears when net impedance ZL is at its lowest and just then the signal is not cut. By high ZL the power consumption is small and the small increase of consumption due to cutting does not have any effect. Even in that respect an advantageous solution.
With respect to interference suppression the invention is advantageous, because usually there is no EMC susceptible feedback (especially when the cutting method is not used controlling the source voltage at the voltage source). On transmission-disturbances across the network have no effect neither on transmitter operation in practise nor EMC-susceptibility tests. Further, it is of great help that disturbances from the network are attenuated and meet at first the low-pass filter or band-pass filter and another interference suppression. As to its costs the cutting system is really profitable. As additional components for instance a capacitor C (e.g. 1 uF, ceramic or plastic capacitor) and two Zener diodes or, alternatively, a VDR resistor or another corresponding component. Generally, the cost price should be kept as low as possible in order to enable serial production and to be able to compete. The invention can be put into practice at low price and works also in bad interference conditions.
The cutting method according to the invention, as in the PCT-publication presented adjusting method of the load signal level, is good enough for many applications in practise in the network as considered in relation to reliable data transmission.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
In the following the invention is disclosed with reference to the enclosed table and drawing figures, where
Table 1 shows load signal UL as function of net impedance ZL without signal cutting and with signal cutting.
FIG. 1 shows a prior art voltage curve.
FIG. 2. is a block diagram of an exemplary embodiment of the invention.
FIG. 3 is a block diagram of another exemplary embodiment of the invention.
FIG. 4 is a graph showing a load signal voltage UL as a function of network impedance ZL achievable by means of the exemplary embodiment of the invention of FIG. 3.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The dots of block diagram marked with small circles are numbered measuring points 5, 11, 15, 21, 31, 41, 51, 61. In association with them an arrow is marked to illustrate voltage and or current symbol.
Block 10 is an adjustable or fixed voltage source, the source voltage US of which is adjustable in measuring point 61 by means of voltage UADJ available from control block 60.
The actual signal to be transmitted (e.g. under 95 kHz, 95-125 kHz, 125-140 kHz or 140-148.5 kHz) can be a sinusoidal or a square signal; input voltage UIN in measuring point 15.
Signal Amplifier 20 is a signal amplifier where the above mentioned input signal is amplified and its great output signal UOUT in measuring point 21 is fed into signal clipper 30. Signal UCLP clipped in this way in measuring point 31 is fed further to the low-pass or band-pass signal filter 40, the output voltage of which UFL is a very clean sinusoidal wave free of harmonic wave components. Signal UFL in measuring point 41 is fed across coupling unit 50 and through transmitter output connector (L-N) to the network, and to ‘ride’ onto the active net voltage UN where it gets in UL size across net impedance ZL in measuring point 51 (UN+UL).
From Coupling Unit 50 output (measuring point 51) signal (UN+UL) is taken to control block 60, which gives directly a control voltage UADJ or another kind of variable proportional to signal UL amplitude in measuring point 61 to control adjustable voltage source 10, the direct source voltage US given by it functions as supply voltage of signal amplifier 20. The greater the US the smaller the UL tends to be and so in signal amplifier 20 the more the UOUT gets clipped from its peak the smaller the US is. In this the UIN is constant all the time as even the voltage amplification of signal amplifier 20. By so great net impedance values the load signal amplitude UL tending to grow is clipped almost to a constant value. By means of control voltage UADJ from control block 60 or another control variable can instead of adjustable voltage source 10 block 20, 30 or 40 be controlled in order to clip or distort the signal.
If, on the other hand, the net impedance ZL is very low, then also UL is very low and US again at its maximum and there is no clipping in signal amplifier 20 and a maximum load signal is achieved to the net impedance. Even by such low net impedances a signal as high as possible can be fed into the network. Control block 60 can get into the UL its proportional instead of measuring point 51 (presented above), for instance from measuring point 21, 31 or 41. Since adjustment of load signal UL into a constant value in adjusting the US is not the most advantageous application, probably more advantageous methods presented in the following will be used in signal clipping in order to keep load signal UL constant.
Block 70 is a receiver and blocks 20-40 can also be controlled by direct voltage proportional to the transmission voltage receivable from receiver 70 or by some other control variable.
In the above description signal clipper 30 was not all in function. In the following control block 60 is removed, while voltage source 10 is continuously feeding constant maximum source voltage USMAX as operating voltage of signal amplifier 20. The amplification of signal amplifier is constant, that is so high that output signal UOUT hardly gets clipped at all or just a little from its peaks. US=source voltage=supply voltage. USMAX=the available maximum magnitude of source voltage US 
An alternative is to clip input signal UIN the more the greater the ZL and UL are. However, if input signal ZIN is kept constant, clipping is carried out in signal clipper 30 in the cheapest way. It takes place so that there is a series resistance in the input connection of signal clipper 30 and after it a capacitor (if needed) followed by two zener diodes, transzorbs, a VDR resistor or some other similar clipping component.
If net impedance ZL is very low, then the output current IOUT of signal amplifier 20 is high. Thereby in serial resistance R of signal clipper 30 there is a great drop of voltage and, for instance, the zener diodes do not clip at all even a whole signal from its top, since the signal voltage across them is so low that the zener voltage is not exceeded. By high ZL values the a the signal will be clipped strongly again. (Ref. FIG. 3).
The signal can be clipped or distorted even in other ways and already in signal amplifier 20 and not until signal clipper 30. It can, for instance, take place as ‘zero point clipping’, whereby the peaks can pass without getting clipped but both signal half periods clipped from their root. It can be carried out by automatic adjustment of base-to-emitter voltages UBE of signal amplifier 20 power transistors in a way dependent on the UL amplitude. UBE=base-to-emitter DC-voltage. For instance, control unit 60 produces control signal UACC or IACC proportional to load signal voltage UL to control the strength of clipping and/or distorting of signal in the Signal Amplifier 20 and/or the Signal Clipper 30. The higher ZL and UL, the stronger the clipping and/or distorting function.
However, common to all adjustment ways is that adjustment takes place clipping the signal in one way or another and that the signals gets strongly distorted. The principle of distortion holds true if the signal amplifier 20 input signal UIN and output signal UOUT are sinusoidal signals. If the signals are square signals, no distortion takes necessarily place even on clipping, since if a square wave is clipped from its peak, in the peak or in the centre, still the signal square shape remains square.
In the following an example is presented of a practical application with reference to FIG. 3 illustrating a practical application.
The supply voltage US of signal amplifier 20 is a regulated direct voltage, e.g. +15 V. Input signal UIN (e.g. 95-125 kHz) can be a sinusoidal or a square wave 5 Vpp. The voltage gain of signal amplifier 20 is constant and of such kind that input signal UIN does not get quite clipped or gets clipped slightly at signal amplifier output (UOUT in measuring point 21). UOUT is as to its amplitude about 15 Vpp either a sinusoidal or a square type signal. There is in signal clipper 30 a serial resistance R (many ohms), a serial capacitor (e.g. 1 uF) and two zener diodes D1 and D2, which do not at low net impedance ZL values clip signal UCLP at all or only slightly but at net impedance ZL high values (e.g. 50 ohm) they clip signal UCLP from its peaks to a level determined by the zener diodes. Clipping is based on the fact that the drop of voltage IOUT×R in resistor R is the lower the higher the net impedance ZL.
Signal UCLP the voltage level of which was made constant on clipping, is fed through low-pass or band-pass signal filter 40 and coupling unit 50 to the network between phase and neutral. TC is a coupling transformer an CC a coupling capacitor.
Galvanic separation from the network takes place by means of net transformer T and the coupling transformer of signal TC. (The coupling transformer could, of course, be even left out and the signal coupled galvanically direct to the network through coupling capacitor CC. However, for electrical safety galvanic separation is good).
FIG. 4 shows the load signal voltage UL achievable by means of this practical application as function of network impedance ZL. UL1 is the load signal level according to the invention. UL2=is the load signal level according to the traditional solution.
By means of supply voltage US=+15 V as level UL and as function of net impedance ZL of signal amplifier 20, without signal clipping (zener diodes D1 and D2 excluded) and with signal clipping (zener diodes(D1 and D2 included) following values are measured:







TABLE 1







Load signal UL as function of net impedance ZL


without and with signal clipping












UL(Vpp)/ZL (ohm)

UL(Vpp)/ZL (ohm)
















D1 and D2 are not
6.0/50
D1 and D2 is are
4.1/50




4.8/5
Invention
3.5/5




4.4/2

3.2/2




3.1/1

2.7/1










If the supply voltage US is increased, then also by very low values (e.g. 1 ohm) of net impedance ZL a higher load signal UL than presented in table 1 and in FIG. 1 is achieved. In practice the significance of this is yet so small that it hardly pays to use an operating voltage higher than US=+15 V.
Also using signal clipper components more effective and better than the zener diodes it is easier to keep the UL constant.

## Claims

1. A method for controlling the load signal of a signal transmitter in a data system sending data in low voltage network in order to maintain the load signal voltage constant, wherein said output signal is coupled to the network by a coupling unit that provides signal coupling to the network, and the method further uses a signal amplifier for producing an output signal and an output current, a signal filter and an voltage source for producing a signal amplifier supply voltage, the method comprising:
clipping the output signal of the signal amplifier, said clipping being dependent on the load voltage of the signal to be sent to the network or dependent on the output current from the signal amplifier.

2. A method according to claim 1 further comprising delivering to the signal amplifier a supply voltage inversely proportional to the load signal of the voltage source.

3. A method according to claim 1 further comprising delivering a signal inversely proportional to the supply voltage of the voltage source under the control of a control unit.

4. A method according to claim 1 wherein, on transmission, a signal to be sent is clipped, using a signal clipper, by clipping an input signal and/or an output signal of the signal amplifier, the output signal of signal clipper and/or of other units being dependent on the load signal voltage or the load signal current in order to maintain the load signal voltage independent of the network impedance.

5. A method according to claim 1 further comprising adjusting the supply voltage of the signal amplifier using an adjustable voltage source, the source voltage of the adjustable voltage source being adjusted using a control unit such that the output voltage of the signal amplifier is also adjusted by said clipping so that the load signal voltage remains constant and independent of the network impedance.

6. A method according to claim 1 further comprising adjusting the signal voltage associated with said signal amplifier and said signal filter is using a direct voltage or another adjusting variable proportional to the load signal that is derivable from a system receiver.

7. A method for controlling the load signal of a signal transmitter in a data system sending data in low voltage network in order to maintain the load signal voltage constant, wherein said output signal is coupled to the network by a coupling unit that provides signal coupling to the network, and the method further uses a signal amplifier for producing an output signal and an output current, a signal filter and a voltage source for producing a signal amplifier supply voltage, the method comprising:
clipping an input signal to said signal amplifier, said clipping being dependent on the load voltage of the signal to be sent to the network or dependent on the output current from the signal amplifier.

8. A method according to claim 7 further comprising delivering to the signal amplifier a supply voltage inversely proportional to the output signal of the operating source.

9. A method according to claim 7 further comprising delivering a signal inversely proportional to the source voltage of the voltage source under the control of a control unit.

10. A method according to claim 7 wherein, on transmission, the signal to be sent is clipped, using a signal clipper, by clipping an input signal and/or an output signal of the signal amplifier, the output signal of signal clipper and/or of other units being dependent on the load signal voltage or the load signal current in order to maintain the load signal voltage independent of the network impedance.

11. A method according to claim 7 further comprising adjusting the supply voltage of the signal amplifier using an adjustable voltage source, the output voltage of the adjustable voltage source being adjusted using a control unit such that the output voltage of the signal amplifier is also adjusted by said clipping so that the load signal voltage remains constant and independent of the network impedance.

12. A method according to claim 7 further comprising adjusting the signal voltage associated with said signal amplifier and said signal filter is using a direct voltage, or another adjusting variable proportional to the load signal, that is derivable from a system receiver.