MXPA00001607A - Drive circuit for reactive loads - Google Patents

Abstract

A highly efficient resonant switching driver circuit (10) includes a matching reactance (16) coupled between a resonant antenna (12) and a driver circuit (14). The matching reactance performs a series to parallel impedance match from the driver circuit to the antenna.

Description

EXCITATION CIRCUIT f »A &A REACTIVE LOADS BACKGROUND OF THE INVENTION The present invention relates generally to a circuit for driving a reactive load and, in particular, to a highly efficient resonant switching circuit for converting direct current into sinusoidal circulating currents with radio frequency reactive charges. The present invention can be used, for example, to excite reactive (inductive) loop antennas such as those used in an interrogator for an electronic article surveillance (EAS) arrangement. An excitation circuit with a resonant circuit is commonly used to allow the efficient conversion of energy from an electrical power supply into current to a reactive load. Figure 1 shows, in a generalized manner, an excitation circuit 100 according to the prior art to excite a reactive (inductive) load 102 (Ls). The excitation circuit 100 includes a current switching device Qs, a resonance capacitor (Cs) and a loss element of (Ro), the loss element representing the energy losses associated with the reactive load resistors Ls 102 and the capacitor Cs and any additional resistance that may be connected to the circuit 100. The design of the circuit 100 is optimized to supply active energy to the loss element (Ro), instead of reactive power to the inductive load (Ls). Thus, the performance analysis of the circuit 100 is commonly related to the amount of active energy supplied to the loss element (Ro). The following description refers to this common method of analysis. (An additional resistor can be incorporated as part of the resonant circuit comprising Ls and Cs, for example, to increase the resonance bandwidth). Figure 2 shows the voltage and current waveforms 102, 104 typically associated with the excitation circuit 100. The upper waveform 104 shows the voltage (Vs) through the current switching device Qs and the resulting capacitor Cs of the current switching performed by the current switching device Qs. The lower waveform 106 shows the current (lis) circulating through the reactive load Ls. It is convenient to operate the excitation circuits for reactive loads with the highest possible performance. Inefficient excitation circuits require greater supplies of electrical energy. Inefficient excitation circuits also waste substantial energy in the form of heat, and thus require large heat sinks and / or cooling fans to remove heat, and are often less reliable. The nature of the current switching device Qs determines the efficiency of the drive circuit 100 according to the prior art. In particular, the percentage of time in which the switching device Qs is made to operate in a linear mode, a mode in which the current is varied as a continuous function of time instead of an activated / deactivated function of time, determines the so-called operation class of the excitation circuit 100 according to the prior art. In reactive charge exciter circuits, such as excitation circuit 100, the energy conversion performances are generally referred to as the energy dissipated by the loss element Ro (the resistive losses of the circuit). In this way, the energy conversion efficiency is the percentage of energy dissipated in Ro divided by the total energy consumed by the excitation circuit 100 (the sum of the energy supplied to Ro and the energy dissipated by the switching device Qs of current). The commonly known classes of operation of the excitation circuit 100 are Class A, Class B and Class C. Operation of Class A relates to the operation of Qs in the linear mode for 100% of the time. Operation in Class A is inefficient due to the energy dissipated through the switch of the current switching device Qs. This energy dissipation is caused by the simultaneous voltage across and current circulation by the current switching device Qs, which is due to the linear mode of operation of Qs. The operation in Class A of the excitation circuit 100 according to the prior art has a theoretical maximum yield of 25%. The Class B operation of the circuit 100 refers to the operation of the current switching device Qs in the linear mode for approximately 50% of the time. In other words, the switching device Qs is operated linearly for about one half of each cycle of the excitation waveform. The theoretical maximum energy conversion performance for Class B operation of circuit 100 according to the prior art is 78.65%, although practical implementations often obtain a performance of less than 50%. The Class C operation of the circuit 100 refers to the operation of the current switching device Qs in the linear mode for less than 50% of the time. In fact, the Class C operation of the circuit 100 can operate the current switch device Qs predominantly as an on / off switch, which in this way does not make it suitable for truly linear amplification applications. The driving time diagram shown in Figure 2 is for Class C operation. Class C operation of circuit 100 according to the prior art achieves the highest performance performance, often comprised between 40% and 80% in practical applications. Such performances do not yet meet the objective of the present invention. Figure 3 shows a return drive circuit 108 according to the prior art, which is commonly used as a horizontal deflection drive circuit in cathode ray tube displays (televisions and monitors). When used as a deflection excitation circuit in cathode ray tubes, the exciting circuit 108 includes a high voltage transformer (Ls), a current breaking device (Qs), and a resonance capacitor (Cs). The excitation circuit 108 may also include a high capacitance coupling capacitor (Cc), to prevent the direct current from flowing through inductance (Lo) of deflection coils which would cause horizontal positioning errors in the cathode ray tube screen . The drive circuit 108 can be characterized as a resonant interruption drive circuit because the current breaker device Qs is operated strictly in the on / off mode. The resonant part of the excitation circuit 108 is formed by the parallel combination of the deflection coil (Lo) and the high voltage transformer (Ls) in conjunction with the resonance capacitor (Cs). When operated as a horizontal deflection circuit, the current switching device Qs is closed during the sweep (approximately 80% of the total period), causing a flat-bottomed voltage waveform to be applied across the coil of reflection (Lo). (See the waveform Vs and Vo in figure 3). During the time that the current switch device Qs is connected, the supply voltage (Vsp) is applied through the inductors (Ls) and (Lo). As is well known in the art, the currents circulating through Ls Lo increase linearly during this time. This linear increase in current is convenient because it produces a more or less linear deflection of the cathode ray tube electrons as a function of time, thus producing a more or less uniform distribution of information through the screen of the cathode ray tube. When the switching device Qs opens during the so-called return time (approximately 20% of the total period), the energy stored in the inductors Ls and Lo is transferred in a resonant manner to the resonance capacitor (Cs). This results in the generation of a medium high-voltage sinusoidal signal through the capacitor (Cs), whose peak is of a much higher amplitude than the voltage (Vsp) of the power supply. In this way, the voltage across the inductors Ls and Lo is inverted, compared to the voltage applied therethrough when the device Qs current switch was closed, thereby making the current flow through the devices. to invert, which in turn causes the capacitor (Cs) to discharge and transfer its stored energy back to the combination of the inductors Ls and Lo. This loading and unloading of the capacitor (Cs) is known as return and occurs in a sinusoidal manner, thereby reducing the sinusoidal return pulse means which are indicative of the operation of the drive circuit 108. The return drive circuit 108 converts DC power in reactive energy at radio frequency frequency very efficiently. As the device (Qs) current switch is used as a switch, and not as a linear device, the energy losses associated with the Qs device can be very low. Unfortunately, the return drive circuit 108 is not suitable for driving an inductive loop antenna because of the high harmonic content of the signal it generates. These harmonics are emitted, thus creating a high level of emissions outside the desired frequency range of radiation, which is unacceptable to government radio regulation authorities, such as the United States Federal Communications Commission. America. Figure 4 shows a Class E driving circuit 110 according to the prior art for driving an inductive load (Lo). Circuit 110 includes a current-interrupting device (Qs), a switch capacitor (Cs), an output inductor (Lo), (which can be an inductive loop antenna), and a loss element (Ro), representing the loss element the energy losses associated with the resistances of Ls, Cs, Co, Lo and any additional resistance that may be connected to the circuit 110. (As in the case of the circuit 100 of Figure 1, a resistor may be included additional as part of the resonant circuit comprising Lo and Co, for example, to increase the resonance bandwidth). Figure 5 shows the voltage waveform and the current waveform associated with the Class E drive circuit 100. A reverse sunusoidal pulse means 112 is produced in the switch device Qs by the switch capacitor (Cs) , the output inductor (Lo) and the resonance capacitor (Co). A distinctive feature of the Class E circuit 110 is that the alternating current component of the current (lis) 114 in the switch inductor (Ls) is much smaller than the direct current 116 flowing through the switch inductor (Ls) In the Class E excitation circuit 110, the current interrupting device Qs is operated as a switch, either switched on or off. When connected, the current interrupting device Qs conducts for the low voltage portion of the half-wave sinusoidal and therefore, less energy is dissipated. When disconnected, no current flows through the current interrupting device Qs, and therefore energy is essentially not dissipated. In the Class E excitation circuit 110, the DC supply inductor Ls has a high value in relation to the output inductor Lo, and therefore does not affect the resonance operation of the circuit 110. The resonant frequency of the inductor of The output Lo and the resonance capacitor Co are chosen to be nominally at Fo, the interruption frequency of the current interrupting device Qs. This will cause the resonant circuit comprising Lo and Co to filter the harmonics of the average sinusoidal signal generated through the switch Qs, thus ensuring that the output of the signal emitted from the inductor Lo is largely free of unwanted harmonics. The half sinusoidal portion of the signal Vs shown in Figure 5 is the result of the combined action of Cs. C and Lo. In a practical implementation of the Class E exciter circuit 110, the resonant frequency of Cs, Co and Lo may be slightly higher than the operating frequency Fo. This is to ensure that the signal Vs returns to ground before the power switch Qs is connected. This minimizes the power losses of the current switch Qs associated with the interruption. It has been determined that a practical implementation of the E-Class excitation circuit for use as a loop antenna driver is not suitable because a practical interruption device Qs comprises a field effect transistor (FET) having a large capacity. of non-linear device. This capacitance of the device is maximum when the voltage across the device (Vs) is minimal. In practice, this large capacitance of the non-linear device causes the resonance frequency of the circuit to be much lower during the immediate period after the field effect transistor is off. This tends to lock the circuit so that the excitation voltage (Vs) is kept low long after the field effect transient is off. This interlocking effect may last more than one cycle, until the current flowing through the DC power inductor (Ls) increases sufficiently to charge the large non-linear capacitance of the field effect transistor enough to draw the circuit of this state. Thus, in a practical implementation of the Class E exciter circuit 110, the excitation signal cycles can be skipped, due to the interlock, either periodically (generating a subharmonic signal) or randomly (generating a chaotic form of noise). . Thus, a practical implementation of the Class E exciter circuit 110 is not suitable for use as an exciter for a reactive load such as a loop antenna. The Class A, B and C and return exciters are more immune to such problems because the resonance of these circuits controls their operation to a much greater extent than that of the Class E circuit. The Ls inductor in the excitation circuits 100 Class A, B and C of Figure 1 and the excitation circuit 108 and the fluyback of Figure 3 is relatively much smaller than the inductor Ls of the Class E excitation circuit 110. With a relatively small value of Ls, the increase in current through Ls (associated with the voltage applied through it when the current switch QS is conducting) loads the non-linear capacitance of the practical interruption devices Qs (as it is a transistor). field) sufficiently fast so that the interlocking described above does not occur. However, circuits that use these operating classes (A, B, C) are inefficient or generate unacceptable harmonics. Despite the availability of many different types of driver circuits, there is still a need to have an exciter circuit that can efficiently excite reactive loads without the introduction of excessive noise or harmonics and that is suitable for driving an inductive loop antenna. The present invention meets such needs.

BRIEF DESCRIPTION OF THE INVENTION Briefly, the present invention comprises a circuit for driving a reactive load, such as an inductive load or a capacitive load, with high efficiency. The circuit comprises a driving circuit and a coupling reactance, the coupling reactance being a capacitor or an inductor. The driver circuit converts DC input current into radio frequency output current. The reactance is coupled between the radio frequency output of the driver circuit and an output resonant circuit. One element of the output resonant circuit is the reactive load. The coupling reaquence performs a series-to-parallel correspondence of the impedance of the driver circuit with the output resonant circuit. Another embodiment of the present invention comprises a circuit for driving a reactive load with high efficiency, having a driver circuit, an output resonant circuit, an element which is the reactive load, and a coupling reactance, the coupling reactance being a capacitor or an inductor. The driver circuit converts continuous DC input current into radio output current. The output resonant circuit has an input to receive the radio frequency output current. The coupling reactance is connected in series between the radiofrequency current output of the driver circuit and the input of the resonant circuit to effect a series to parallel impedance correspondence of the exciter circuit to the resonant circuit. Yet another embodiment of the invention comprises a circuit for driving a reactive load with high efficiency having a driver circuit comprising an electronic current switch, a return inductor and a return capacitor configured to generate a radio frequency output current, a output resonant circuit, an element that is the reactive load, and a coupling reactance, the coupling reactance being a capacitor or an inductor. The driver circuit generates a radio frequency output current by periodically opening and closing the circuit breaker at the operating radio frequency so that during the period when the circuit breaker is closed, the voltage across the circuit breaker approaches zero, and during the At the time the switch is open, a sinusoidal half waveform is created due to the resonant action of the return inductor and the flayback capacitor. The output resonant circuit has an input to receive the radio frequency output current. The coupling reactance is connected in series between the radiofrequency current output and the driver circuit and the input of the resonant circuit to effect a serial impedance matching in parallel from the driver circuit to the resonant circuit. Another embodiment of the present invention comprises an electronic monitoring arrangement for articles having an interrogator for monitoring a detection zone by transmitting an interrogation signal to the detection zone and detecting alterations caused by the presence of a resonant protector within the detection zone. detection. The interrogator comprises a loop antenna for transmitting the interrogation signal, a resonance capacitor connected through the antenna and a driver circuit, the resulting resonant circuit. The driver circuit has a radio frequency output current and a coupling reactance connected in series between the radiofrequency current output of the driver circuit and the resonant circuit of the antenna. The inductor performs a series-to-parallel impedance matching of the driver circuit to the resonant circuit of the antenna.

BRIEF DESCRIPTION OF THE DRAWINGS The brief description, as well as the following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the accompanying drawings. For illustrative purposes of the invention, embodiments that are currently preferred are shown in the drawings. However, it should be understood that the invention is not limited to the precise arrangements and instrumentation shown. In the drawings: Figure 1 is a schematic electrical diagram of an excitation circuit according to the prior art for exciting a reactive load.

Figure 2 shows voltage and current waveforms associated with the drive circuit of Figure 1. Figure 3 is an electrical schematic diagram of a return driver circuit according to the prior art. Figure 4 is a schematic electrical diagram of a class E power amplifier according to the prior art using to excite a reactive load. Figure 5 shows voltage and current waveforms associated with the circuit of Figure 4. Figure 6 is a schematic functional block diagram of a circuit according to the present invention that is used to drive a reactive load. Figure 7A is an equivalent electrical circuit diagram of a preferred implementation of the circuit of Figure 1 in a single-ended configuration. Figure 7B is an equivalent electrical circuit diagram of the circuit of Figure 7A in a symmetric configuration. Figure 8 shows forms of voltage and current waves associated with the circuit of Figure 7A; and Figure 9 is a schematic functional block diagram of an interrogator suitable for use with the present invention.

In the present specification certain terminology is used for convenience only and should not be taken as limiting the present invention. In the drawings, the same reference numbers are used to designate the same elements in all figures. Figure 6 shows a schematic block diagram of a circuit 10 according to the present invention that is used to excite a reactive load. In the embodiment of the invention shown in Figure 6, it is shown in output resonant circuit 12 comprising at least one inductor and one capacitor, one of which is the reactive load. The inductor can be an inductive loop antenna. The reactive can comprise an inductive load or a capacitive load. Figure 7A shows a circuit diagram of a preferred implementation of the circuits 10 and 12. With reference to Figure 6, the circuit 10 includes a driver circuit 14, a coupling or matching reactance (Lm) 16 and a capacitor coupling (Cc) 18 optional. The driver circuit 14 converts a direct current supply into a radio frequency output current. The correspondence reactance (Lm) 16 is coupled in series between a radiofrequency output 15 of the energized circuit 14 and the input of the resonant circuit 12. According to the present invention, the reactance 16 may comprise a capacitor or an inductor, the reactance of correspondence 16 can comprise a capacitor or an inductor. The correspondence reactance (Lm) 16 affects a series-to-parallel impedance matching of the output of the driver circuit 14 to the circuit (Cc) 18, the correspondence reactance (Lm) 16, and the reactive load, Co or Lo, which is part of the output resonant circuit 12. The driver circuit 14 has certain components associated with a class E power amplifier, including an interrupter device (Qs), a switch inductor (Ls) and a switch capacitor (Cs) . The equivalent resistance to the resonator of the driver circuit 14 is represented as Rs. The interruption device (Qs) is preferably a power metal oxide semiconductor field effect transistor (MOSFET), but may also comprise any suitable electronic switching device, such as a bipolar power transistor (BJT), a Isolated gate bipolar transistor (IGBT), a controlled MOS thyristor (MCT), or a vacuum tube. Figure 7A shows the driver circuit 14 implemented as a single-ended configuration, in which the active devices continuously drive. However, the driver circuit 14 may also be implemented as a symmetric configuration, as shown in Figure 7B, (ie differential implementation), in which there are at least two active devices that alternately amplify the negative and positive cycles of the input waveform. Referring now to Figure 7B, a symmetric configuration of a circuit 10 'is shown to drive a reactive load 12'.

The circuit 10 'comprises a driver circuit 14', which is shown in the form of an equivalent circuit, which includes a pair of coupling capacitors (Cc) 18 ', a pair of matching reactors (Lm) 16', and the reactive load , which is part of a resonance circuit is output 12 '. According to the symmetric figure, the driver circuit 14 'includes a pair of interrupting devices (Qs), a pair of switch inductors (Ls) and a pair of switch capacitors (Cs). The equivalent output resistance of the driver circuit 14 'is represented as resistors Ls. As will be understood by those skilled in the art, the symmetric configuration can have a higher energy conversion efficiency and higher output current than the single-ended configuration. The symmetric configuration also has other advantages such as being harmonic content of even-order form nominally canceled. That is, a sinusoidal half-wave half-wave return interrupt output of the driver circuit 14 (which is described in detail below with reference to FIG. 8) only produces harmonic content in even order and does not produce harmonic order content. odd. In the symmetric configuration, the components of even order substantially cancel each other out, so that substantially no harmonic content is created. In practice, it is difficult to produce a perfect sinusoidal mean return waveform, so that complete cancellation can only be approximated. Referring again to Figure 7A (and in contrast to Figure 7B), the coupling capacitor (Cc) 18 blocks the average DC voltage associated with the driver circuit 14 to appear in the output resonant circuit 12. The value of the capacitor 12 is sufficiently large so that it does not affect the operation of the circuit 10. The correspondence reactance (Lm) 16 effects a series-to-parallel impedance matching of the driver circuit 14 (having a resistance (Rs)) to the load ( having a parallel equivalent resistance (Rp), which represents the output resistance of the resonant circuit 12). The resistance (Rs) of the driver circuit 14 is lower than the resistance (Rp) of the output or load. The resonant circuit 12 is not lossless. Accordingly, some electrical power must be applied to the resonant circuit 12 for a given circulation current. In resonance, the power consumption can be represented by the parallel equivalent resistance Rp, which is generally too high (for example, from 3kO to 10kO) to allow the resonant circuit 12 to be directly connected to the output of the driver circuit 14. If such a direct connection were made, the energy transfer would be very inefficient and insufficient energy would be transferred. It is convenient to transform this high resistance into a lower resistance (e.g., 5-20 O) to match the resistance of the interrupting device (Qs) and its resonance, which allows sufficient power to be provided to the resonant circuit 12 for allow circuit 12 to excite the reactive load.

Figure 8 shows voltage and current waveforms associated with the driver circuit 14 of Figure 7A. The upper waveform 20 shows the waveform (Vs) of input interruption voltage, and the lower waveform 22 shows the current (lis) through the switch inductor (Ls). The voltage waveform 20 of the input switch is a half wave sinusoidal. When the interrupting device (Qs) is energized or closed, the waveform 20 falls to the ground (OV) for approximately one half of the operating period. The inductor (Ls) of the switch is charged with an increasing current flow as the supply voltage (Vsp) is dropped through it. As the current circulation increases through the inductor (Ls), an increasing amount of energy is stored in the inductor (Ls). When the interrupting device (Qs) is deenergized or open during the other half of the period, the waveform (Vs) increases to a peak voltage sinusoidally, and the current stored in the inductor (Ls) discharges while charging the capacitor (Cs) of the switch until the energy stored in the inductor (Ls) is transferred to the capacitor (Cs). The peak voltage at this point is directly related to the same energy now stored in the capacitor (Cs) as it was stored in the inductor (Ls). The peak voltage causes a reverse current to start circulating in the inductor (Ls). The reverse current causes the capacitor (Cs) to be discharged sinusoidally until the waveform (Vs) returns to ground. With the present invention, the inductor (Ls) and the capacitor (Cs) are dimensioned so that the sinusoidal half-point formed in this way is completed in a quarter to a half of the operating period. In the present specification this part of the waveform is referred to as the "return pulse", and is similar in certain aspects to the waveform of the above-mentioned cathode ray tube scanning circuit. The half sinusoidal or return pulse has a limited speed that gives the interruption device (Qs) time to deactivate while the voltage (Vs) is increasing and the transition losses due to interruptions in the interruption device (Qs) are reduced. When the connecting device (Qs) is connected, there is little or no voltage drop across it for the current flowing through it. In this way, little energy is wasted. On the contrary, when the interruption device (Qs) is disconnected, no real current flows through it (except capacitive) while there is voltage across it. In this way, even if there is a voltage drop through the interruption device (Qs), little energy is wasted. Theoretically, circuit 10 can have a performance of 100%. Actually, losses occur as a result of the finite resistance of the closed interruption device (Qs), as well as losses associated with the finite time required for the interruption device (Qs) to pass from connection to disconnection. Typically, the yields are about 80-90%.

Ideally, the inductor (Ls) and the capacitor (Cs) of the interruption resonator are dimensioned so that, when they are damped by the load, (output resonant circuit 12), they will lose all of their stored energy at the end of the half sinusoidal point. This condition occurs during approximately% of the resonant frequency cycle (Fs) of the interrupting resonator. In the presently preferred embodiment, the switch inductor (Ls) and the capacitor (Cs) of the switch produce an interruption resonance frequency (Fs) comprised between one to two times the operating frequency (Fo) of circuit 10. The peak voltage viewed by the interruption device (Qs) during a perfect sinusoidal half return waveform is approximately 2.57 times the supply voltage (Vsp). This is due to the fact that the average voltage across the inductor (Ls) must be equal to zero. In this way, the voltage-time product for the connected or low part must be equal to the voltage-time product for the disconnected or high part of the waveform. If the return pulse were a true sinusoidal half-wave, then the peak voltage reached would be p / 2 or approximately 1.57 times the supply voltage (Vsp) over the supply voltage (Vsp), or about 2.57 times the voltage of feeding in relation to land. Since the natural period of the switch 1 / Fs resonator is shorter than a cycle of the operating frequency (Fo), the peak voltages are generally higher. Peak voltages are typically equal to three times the supply voltage (Vsp). * * - 3 - * r ^ ft -sp- -ss-aa *. ^, ¿'' '-. ^ Ía-í-fi:' 1 .- As shown in the form of lower wave 22 of FIG. 8, a distinguishing feature of the driver circuit 14 is that the alternating current component of the current in the inductor (Ls) is greater than the direct current (Idc). The alternating current component of the current in the inductor (Ls) causes the current (lis) to be periodically negative. This negative current approaches zero in the ideal driver circuit 14. Also, the current in the inductor (Ls) is not sinusoidal. The reactance of the inductor (Ls) and the capacitor (Cs) is much greater than the resistance of the interruption device (Qs) when it is activated. The Q of the interrupting resonator is less than one when the interrupting device (Qs) is conducting, and greater than two or equal to two when the interrupting device (Qs) is not driving. An essential difference between the driver circuit 14 and a class E amplifier according to the prior art is that the driver circuit 14 contains a relatively large resonant current in the interrupter device (Qs) keeping the inductor value (Ls) relatively small to eliminate the interlocking tendency of the class E amplifier, mentioned above. Because the Q of the interrupting resonator is less than one when the current switch Qs is connected, the waveform generated by the exciter is determined predominantly by the switch, whereas in the class A, B and C exciters, The waveform is determined predominantly by the resonator. In this regard, the driver circuit 14 is similar to the sweep circuit 3 of the above-mentioned cathode ray tubes, differing in the aggregate of the output matching circuit (correspondence reactance 16). The operation controlled with the switch is highly efficient. As noted above, the correspondence reactance (Lm) 16 converts the equivalent equivalent resistance of the output resonant circuit 12 (which is a resonant antenna comprising an antenna output capacitor (Co) and an inductor (Lo) of output antenna) in an equivalent series resistance that is required to consume the correct output energy of the exciter circuit 14. When the correspondence reactance (Lm) is an inductor, an additional benefit is that it forms a two-pole sink filter with the output capacitor (Co). This provides reduction of the harmonic energy generated by the driver circuit 14. Efficient circuits naturally generate significant harmonic energy due to the nature of circuit switching. Thus, for most applications where a single frequency output is desired, this harmonic energy must be filtered and must prevent it from reaching the output. The value of the inductor (Lo) of the output antenna is generally fixed due to known physical restrictions on the antenna, such as possible size, radiation configuration, and the like. The value of the output resonance capacitor (Co) is selected to resonate the output inductance (Lo) at the operating frequency (Fo), and is adjustable to allow the circuit 12 to be tuned precisely to the operating frequency. (Fo), and can be determined by the following formula: Co = 1 / (4 p2Fo2Lo). The equivalent parallel resistance (Rp) is determined primarily by the Qo of the output resonance circuit 12 and to a much smaller extent by the correspondence inductor 16, and can be determined by means of the following formula: Rp = QoXLo where XLo = 2pLoFo. To pass a predetermined current through the reactive load, in this case, Lo, a corresponding voltage Vo must be developed through the load, and a corresponding power Po must be supplied from the exciter circuit 14. The power required it depends on the Q of the output resonant circuit 12, which is inversely related to the losses of the resonant circuit 12. For the given current: Vo = loXLo; and Po = Vo2 / Rp Where Po is the power to be delivered by the driver circuit 14, and Xlo is the impedance of the reactance that is being excited. The excitation resistance (Rs) is determined by the power provided at the output of the driver circuit 14 based on the supply voltage (Vsp). Since the signal from the driver circuit 14 is typically filtered before the output, only the fundamental frequency component of the excitation signal provides significant power. Also, since the waveform of the interruption device (Qs) is generally square at its bottom, the peak voltage of the fundamental frequency component of the excitation signal is generally equal to the supply voltage (Vsp). The effective voltage of the fundamental frequency component of the excitation signal is: RS = 0.51 / 2Vsp or Vd = 0.7071 Vsp. Then, the excitation resistance (Rs) can be calculated by the following formula: Rs = 0.5 Vsp2 / Po. The correspondence reactance (Lm) is dimensioned so that its reactance at the operating frequency is the geometrical mean between desired excitation resistance (Rs) and equivalent parallel resistance (Rp) of the output resonant circuit 12. In this condition, the Parallel resistance (Rp) produces a certain (Qm) for the inductor (Lm) which is the ratio of the reactance to the resistance measured at the operating frequency. The series resistance (Rs) reflected also produces the same (Qm). The relation is defined as follows: QmRs = Rp / Qm = X1 m; or X1 m = (Rs Rp) 1/2; and Lm = X1m / (2nFo).

In this way, this value of the reactance (Lm) is determined which is inversely proportional to the square root of the power supplied to the output. A preferred minimum value of the input capacitor (Cs) is selected by providing a Q of approximately two to the anticipated excitation resistance for the power supplied. This Q value causes the resonant energy of the interrupting device (Qs) to be used completely at approximately% of the resonant cycle of the interrupting device (Qs). At the end of this period, the return portion of the interruption waveform has returned to just zero, ready for the next interruption in time. As the resonance of the switch is parallel: Xcs < Rs / 2; and Cs = 1 / (2pFsXcs), where Xcs is the impedance of the switch capacitor (Cs). In practice, the capacitor (Cs) of the switch is dimensioned so that it minimizes the effects of the non-linear output capacitance of the interruption device (Qs).

If these non-linear effects are not addressed, they can lead to sub-harmonic or chaotic combinations as noted above. A preferred maximum value for (Cs) is equal to the maximum capacitance of the current switch (Qs). Under these conditions, the switch capacitor (Cs) is often larger than necessary to produce the cushioned return waveform described above. This results in higher currents in the switch resonator. Any undamped energy (inverted lis) remaining at the end of the return pulse attempts to send the waveform of the interruption device (Qs) below ground to continue the sine wave. This is taken up by inverter iodos (not shown) normally associated with the interrupt device (Qs) itself. The result is that it causes this inverter current of the stored reverse switch to flow back into the supply, thereby returning stored energy in excess to the supply. Then, there is no upper limit for the size of the capacitor (Cs) of the switch. However, an excessively large capacitor (Cs) wastes energy unnecessarily due to the losses associated with the components comprising the interruption resonator (Qs). The inductor (Ls) of the switch is dimensioned to produce a resonant interrupting frequency of one to two times the operating frequency, as follows: Fo < Fs < (2Fo); and Ls = 1 / (4n2Fs2Cs). Figure 9 is a schematic block diagram of an interrogator 24 suitable for use of the present invention. The interrogator 24 and a resonant shield 26 communicate with inductive coupling, as is well known in the art. Interrogator 24 includes a transmitter 10", a receiver 28, an antenna assembly 12", and data processing and control circuitry 30, each of which has inputs and outputs. The output of the transmitter 10"is connected to a first input of the receiver 28, and to the input of the antenna assembly 12". The output of the antenna assembly 12"is connected to a second input of the receiver 28. A first output and a second output of the data processing and control circuitry 30 are connected to the input of the transmitter 10" and a third input to the receiver 28, respectively. Also, the output of the receiver 28 is connected to the input of the data processing and control circuitry 30. Interrogators having this general configuration can be constructed using circuitry described in U.S. Patent No. 3,752,960; 3,816,708; 4,223,830 and 4,580,041, all issued in favor of Walton, and all of which are incorporated herein by reference in their entirety. However, the transmitter 10"and the antenna assembly 12" include the properties and characteristics of the circuit and the output resonant circuit 12, described above. That is to say, the transmitter 10"is an excitation circuit 19 according to the present invention and the antenna assembly 12" is part of the output resonant circuit 12 according to the present invention. The interrogator 24 may have the physical appearance of a pair of pedestal structures, although other physical manifestations of the interrogator 24 are within the scope of the invention. The interrogator 24 can be used in electronic security arrangements of articles that interact with conventional resonant protectors or with radio frequency identification protectors. Due to the high performance of excitation circuit 10, it is particularly useful when implemented as a small printed circuit board using surface mounted components, where heat dissipation is difficult. The exciter circuit of the present invention can control 2000 voltamps of circulating antenna energy at 13.5 MHz, with approximately 20W of power while maintaining the harmonics at approximately 50 decibels below the carrier frequency. This amount of antenna power is enough to create an interrogation zone for a six-foot corridor using an antenna on each side of the corridor. Those skilled in the art will appreciate that changes may be made to the embodiments described above without departing from the broad inventive concept thereof. Therefore, it should be understood that this invention is not limited to the disclosed disclosures, but is intended to cover modifications within the spirit and scope of the present invention as defined in the appended claims.

Claims (15)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A circuit for exciting a reactive load with high efficiency, the circuit comprising: an exciter circuit for converting DC input to radio frequency output current, the exciter circuit has a differential implementation that includes a first switch and a second switch; an output resonant circuit including the reactive load, and a coupling reactance coupled in series between the radiofrequency current output of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series-to-parallel impedance match of the driver circuit with the output resonant circuit, the coupling reactance includes a first reactance coupled in series between the radio frequency output current of the exciter circuit associated with the first switch and an input of the output resonant circuit, and a second coupled reactance in series between the radiofrequency output current of the excitation circuit associated with the second switch and an input of the output resonant circuit.
2. 2. A circuit for exciting a reactive load with high efficiency, comprising: an exciter circuit for converting direct current input to radio frequency output current, the driver circuit has a differential implementation, ie, a first switch and a second switch; an output resonant circuit that includes the reactive load and an input to receive the radio frequency output current; and a coupling reactance electrically connected in series between the driver circuit and the resonant circuit input to effect a series of series-to-parallel impedance matching of the driver circuit to the output resonant circuit, the coupling reactance includes a first reactance coupled in series between the radiofrequency output current of the excitation circuit associated with the first switch and an output resonant circuit input, and a second reactance coupled in series between the radio frequency output current of the excitation circuit associated with the second switch and an input of the resonant output circuit.
3. 3. In an electronic article surveillance system, an interrogator for monitoring a detection zone transmitting an interrogation signal to the detection zone and detecting alterations caused by the presence of a resonant protector within the detection zone, comprising the interrogator: a loop antenna for transmitting the interrogation signal; a resonance capacitor connected through the antenna forming the antenna and the capacitor a resonant circuit; and an exciter circuit having a radiofrequency current output to drive the resonant circuit, the driver circuit has a differential implementation that includes a first switch and a second switch, the circuit including a coupling reactance connected in series between the output of The radio frequency current of the exciter circuit and the resonant circuit for effecting a series-to-parallel impedance matching of the driver circuit to the resonant circuit, the coupling reactance includes a first reactance coupled in series between the radio frequency output current of the exciter circuit associated with the first switch and an input of the output resonant circuit, and a second reactance coupled in series between the radio frequency output current of the excitation circuit associated with the second switch and an input of the output resonant circuit.
4. 4. A circuit to excite a reactive load with high efficiency, the circuit comprising: an exciter circuit for converting direct current input to radio frequency output current, the driver circuit includes only one switch, the driver circuit also includes a capacitor switch and an inductor switch, the switch has a non-linear output capacitance, the capacitor switch being equal to a maximum of the output capacitance of the switch to minimize the effects of the non-linear output capacitance of the switch, wherein the capacitor switch has a value of (1 / (2pFsXcs)), where Xcs <; Rs / 2, Fs being the resonance frequency of the switch, Xcs being the impedance of the capacitor switch, and Rs being the series of output resistance of the driver circuit; an output resonant circuit that includes the reactive load, and a coupling reactance coupled in series between the output of radio frequency current of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series-to-parallel impedance matching of the driver circuit to the output resonant circuit.
5. 5. A circuit to excite a reactive load with high efficiency, the circuit comprising: an exciter circuit for converting direct current input to radio frequency output current, the driver circuit includes only one switch, the driver circuit also includes a capacitor switch and an inductor switch, the switch has a non-linear output capacitance, the capacitor switch being equal to a maximum of the output capacitance of the switch to minimize the effects of the non-linear output capacitance of the switch, wherein the inductor switch is select to have a value of (1 / (4p2Fs2Cs)), where Fo < Fs < 2Fo, Fs being the resonance frequency of the switch, Cs being the value of the capacitor switch, and Fo being the operating frequency of the circuit; an output resonant circuit including the reactive load, and a coupling reactance coupled in series between the radiofrequency current output of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series-to-parallel impedance match from the exciter circuit to the output resonant circuit. 6.- A circuit to excite a reactive load with high efficiency, the circuit comprising: an exciter circuit for converting direct current input to current d0 * radio frequency output, the exciter circuit includes only one switch, the driver circuit also includes a switch capacitor and an inductor switch, the switch has a non-linear output capacitance, the capacitor switch being equal to a maximum of the output capacitance of the switch to minimize the effects of the non-linear output capacitance of the switch, where the values of the switch, inductor switch and capacitor switch are selected so that the Q of the resonance switch is less than one when the switch is closed and larger than or equal to two when the switch is open; an output resonant circuit including the reactive load, and a coupling reactance coupled in series between the radiofrequency current output of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series-to-parallel impedance match from the exciter circuit to the output resonant circuit. 7 '.- A circuit for exciting a reactive load with high efficiency, the circuit comprising: an exciter circuit for converting direct current input to radio frequency output current, the driver circuit includes only one switch; an output resonant circuit that includes the reactive load; and a coupling reactance coupled in series between the radiofrequency current output of the exciter circuit and an input of the output resonant circuit, effecting the reactance of coupling a correspondence between the series circuit and the parallel circuit of the exciter circuit to the output resonant circuit 8. The circuit according to claim 7, wherein the reactive load consists of an inductive load. according to claim 7, wherein the reactive load consists of a capacitive load 10. The circuit according to claim 7, wherein the coupling reactance consists of a capacitor 11. The circuit of agreement with claim 7, wherein the impedance of the capacitor at the operating frequency of the circuit is a geometric mean between a desired exciter resistance of the driver circuit and an equivalent parallel resistance of the output resonant circuit. claim 7, in which the coupling reactance consists of an inductor. 13. The circuit according to claim 7, wherein the inductor is selected such that its impedance at an operating frequency of the circuit is a geometric mean between a desired exciter resistance of the driver circuit and an equivalent parallel resistance of the circuit resonant output. 14. The circuit according to claim 7, wherein the driver circuit further includes a capacitor switch and an inductor switch. 15. - The circuit according to claim 14, wherein the switch has a non-linear output capacitance, and the capacitor switch is selected to minimize the effects of the non-linear output capacitance of the switch. 16. The circuit according to claim 15, wherein the capacitor switch is equal to a maximum of the output capacitance of the switch. 17. The circuit according to claim 16, wherein the inductor switch and the capacitor switch produce a switch resonance frequency of one to two times the operating frequency of the circuit. 18. The circuit according to claim 7, further comprising a coupling capacitor electrically connected between the driver circuit and the coupling reactance. 19. The circuit according to claim 7, wherein the driver circuit has a single-ended configuration. 20. The circuit according to claim 7, wherein the reactive load consists of a loop antenna. 21. A circuit to excite a reactive load with high efficiency comprising: a driver circuit for converting direct current input to radio frequency output current, the driver circuit includes only one switch; an output resonant circuit that includes the reactive load; and an input to receive the output current ^^^^ ¡igite¡ | ^ | ^ 3 * 7 of radiofrequency; and a coupling reactor electrically connected in series between the driver circuit and the input of the resonant circuit for effecting a series-to-parallel impedance matching of the driver circuit to the resonant circuit. 22. The circuit according to claim 21, wherein the reactive load comprises a loop antenna. 23. The circuit according to claim 21, wherein the output resonant circuit includes a capacitor and a loop antenna connected in parallel. 24. The circuit according to claim 21, further comprising: a coupling capacitor connected in series between the radiofrequency output of the driver circuit and the coupling reactance. 25. The circuit according to claim 21, wherein the coupling reactance comprises an inductor. 26. The circuit according to claim 21, wherein the coupling reactance comprises a capacitor. 27.- A circuit for exciting a reactive load, the circuit comprising: an exciter circuit having only an electronic current switch, a switch inductor, a switch capacitor, the circuit configured to generate a radio frequency output current; an output resonant circuit that includes the reactive load, a coupling reactance, and an input to receive the current from ÉÉH ^^^^ radiofrequency output, where the driver circuit generates the radio frequency output current by periodically opening and closing the switch at the operating radio frequency, so that during the period when the switch is closed, the voltage through the switch approaches zero and during the period when the switch is open, the voltage across the switch has a sinusoidal half waveform, created due to the resonant effect of the inductor switch and the capacitor switch. 28. The circuit according to claim 27, wherein the coupling reactance is connected in series between the radiofrequency current output of the driver circuit and the input of the resonant circuit to effect a series-to-parallel impedance matching of the circuit exciter to the resonant circuit. 29.- In an electronic article surveillance system, an interrogator to monitor a detection zone transmitting an interrogation signal to the detection zone and detect alterations caused by the presence of a resonant protector within the detection zone, comprising the interrogator : a loop antenna to transmit the interrogation signal; a resonance capacitor connected through the antenna forming the antenna and the capacitor a resonant circuit; and an exciter circuit having a radiofrequency current output to drive the resonant circuit, the circuit including a coupling reactance connected in series between the radio frequency current output of the driver circuit and ^ - ákak m ^^ tíáS? the resonant circuit for effecting a series-to-parallel impedance matching of the driver circuit to the resonant circuit, the driver circuit includes only one switch.