SUPPLY CIRCUIT FOR A HALL SENSOR MULTIPLICATION CIRCUIT

Abstract: Supply circuit SC for a Hall sensor multiplication circuit HMC makes it possible to produce both circuits in monolithic technology on a common substrate and yet ac­ complish the polarity reversal of the output voltage U H of the multiplication circuit HMC with such accuracy that at said reversal the absolute value of the voltage U H is changed for only about 0.01% of of its absolute value.

Description: BACKGROUND OF THE INVENTION Technical Field This invention relates to a supply circuit supplying electric current to a Hall sensor multiplication circuit in such a way that the absolute value of the output voltage of the multiplication circuit is changed for about 0.01% at most when the polarity of this output voltage is reversed. Description of the Prior Art In known watthour meters or wattmeters which are based on the Hall effect a multiplication circuit reversing the polarity of the output Hall voltage is used to compensate internal disturbances of the meter. Such meters are described e.g. in DE-A-37 11 978 and DE-A-37 02 344. A known multiplication circuit is composed of a Hall sensor 6' whose first voltage terminal is connected to the inverting input of an operational amplifier A', the second terminal, however, is connected to the output of the multiplication circuit, and of a switching bridge which is made of controlled switches 2', 3', 4', 5' and which supplies electric current across a resistor 7' being connected to one terminal of a load to current terminals of the Hall sensor 6' (Fig. 1). A signal P from a voltage to frequency converter controls the polarity of the Hall voltage U H at the multiplication circuit output by exchanging the current terminals of the Hall sensor 6'. The described multiplication circuit performed in a monolithic technology provides good results when the Hall sensor is performed separatedly from the rest of the multiplication circuit. When, however, the Hall sensor is integrated with the rest of the multiplicaiton circuit on a common substrate the accuracy of the polarity reversal of the Hall voltage U H is affected by the nonideally symmetric shape of the Hall sensor as well as by the nonlinearity originating from a barrier layer separating the Hall sensor from the substrate. EP-A-0 163 460 discloses a system for measuring the electrical energy consumed by a load. The system can be used in an energy meter, or a Watt-meter. The system employs a Hall effect element with supply circuits, and switching means control a relative phase change between the bias current and the magnetic field associated with the Hall effect element to cause thereby a change in the Hall output voltage which is fed to signal processing circuits and measuring circuits to give a measure of the electrical energy consumed, which is independent of errors arising from the self-field effect of the bias current in the Hall effect element. Electrical energy measuring devices employing Hall effect elements are based on the principle that the Hall effect element produces a Hall output voltage proportional to the product of a bias current passing through the element and a magnetic field applied to the element. The magnitude of the bias current and the strength of the magnetic field are proportional to the load voltage and load current respectively. In such devices one of the problems is that the bias current itself produces a magnetic field which generates an error component in the Hall output voltage, referred to as the self-field effect error term. This error term can result in unacceptable inaccuracies of power measurement. The self-field effect error term is also temperature dependent in a non linear manner which makes correction methods difficult. EP-A-0 163 460 suggests for eliminating the problems mentioned above, a system for measuring the electrical energy consumed by a load, including a Hall effect element, and supply circuits for the Hall effect element which are responsive to the load voltage and the load current and include a magnetic circuit for applying a magnetic field to the element and a bias current supply circuit, wherein the supply circuits include switching means operable to effect a relative phase shift between the bias current and the magnetic field at predetermined time intervals and thereby change the phase of a self-field effect error component K sf of the Hall output voltage of the element, a processing circuit is connected to the output of the Hall effect element and is operable to generate in different time periods self-cancelling error signals derived from two different switched phases of the self-field effect error component K sf , and a measuring circuit is operable to receive the processed signals and to register a measurement proportional to the true power W and energy consumption of the load. For removing the influence of an offset voltage of an operational amplifier and an in-phase voltage of a Hall element employed in a Watt-hour meter, PATENTS ABSTRACTS OF JAPAN, vol. 6,, no. 175 (P-141)(1053), September 09, 1982 suggests a method wherein a polarity of a control current applied to the Hall element and an input of a Hall element output to two filters are switched in synchronism with each other. This prior art method uses a circuit where a load voltage is inputted to a voltage-current conversion circuit via a power transformer, a phase-shifting circuit and a first set of analogue switch groups, and is supplied as a control current to a terminal of the Hall element. Meanwhile, a load current is converted into a magnetic field by a core and is applied to the Hall element. The output of the Hall element is inputted to a V/F converter via a buffer amplification circuit, a second set of analogue switch groups, and low-pass filters. Both sets of analogue switch groups are alternately switched and controlled by means of a pulse of duty ratio 50 % from a pulse generator. This eliminates the need to adjust a light load and permits fetching of a Hall output voltage by means of a high input impedance. In accordance with the foregoing background discussion the object of this invention is to provide a supply circuit which will supply a Hall sensor multiplication circuit with electric current whose intensity at a current sense reversal caused by a control signal will be changed for only about 0.01 % of its absolute value, the supply circuit and the multiplication circuit, however, must be able to be produced in a monolithic technology on a common substrate. With the foregoing objects in view, the supply circuit in accordance with the invention comprises the features of claim 1. Claim 2 relates to features of a preferred embodiment of the invention. A specific embodiment of the invention will be presented in the following detailed description in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, Fig. 2 is a graphical illustration of the supply circuit of the invention, and of a Hall sensor multiplication circuit, Figs. 3a,b is a schematic illustration of the supply circuit of the invention and of a negative impedance converter, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The supply circuit SC in accordance with the invention for supplying electric current to a Hall sensor multiplication circuit HMC is shown in Fig. 2. The output O of the supply circuit SC is connected to the current input of the multiplication circuit HMC. At the output of the multiplication circuit HMC, which is performed by Hall sensors SH j , cascade connected through operational amplifiers A j , the voltage U H appears. Load terminals L1,L2 of the supply circuit SC, the load terminal L2 being grounded, are connected to terminals of an external load , whose electric energy or power consumption is measured. Magnetic induction at the Hall sensors SH j is proportional to the electric current through the load causing a voltage drop U L thereon. The terminal L1 is , through a resistor R3 connected, on the one hand through a controlled switch 23 to the first terminal of an adjustable resistor Rk and on the other hand through a controlled switch 24 to the output terminal O of the supply circuit SC. The output terminal O is connected through a controlled switch 26 to the first terminal of a resistor R4 and further through a controlled switch 25 to the first terminal of the resistor Rk . The second terminal of the resistor R4 is connected to the load terminal L2 . The second terminal of the resistor Rk is connected to a common terminal of controlled switches 15,16, the second terminal of these switches being connected to a common terminal of controlled switches 11,13 and 12,14 , respectively, and to the first terminal of a resistor R1 and R2, respectively. The second terminal of the resistors R1,R2 is connected to the output of an operational amplifier A I , which together with the resistors R1,R2 forms a negative impedance converter . The inverting input of the amplifier A I is connected to the second terminal of the switches 11,12 , the noninverting input , however , is connected to the second terminal of the switches 13,14 . The first terminal of the resistors R1,R2 is connected through controlled switches 17 and 18 , respectively , to the output terminal O of the supply circuit SC. The signal input terminal SI of the circuit SC is connected to the control terminal of the switches 23,26 and to the input of a frequency divider 29, and through inverters 27,28 to the control terminal of the switches 24 and 25 ,respectively . The output of the divider 29 is connected to the control terminal of the switches 11,14,15,18 , and through inverters 19,20,21,22 to the control terminal of the switches 13,12,17,16, respectively. The resistances of the resistors R1,R2 are equal , the resistance of the resistor Rk equals the doubled resistance of the load at the output O of the supply circuit SC. For the moment the operation of the supply circuit SC in accordance with the invention will be represented schematically with Figs. 3a,b . Alternately through the switches 9,10 the current -I and +I , respectively , is supplied to the multiplication circuit which is composed of a Hall sensor 6 and of an operational amplifier A (Fig. 3a). Resistors 7,8 symbolically represent oppositely equal resistances with an absolute value equal to the equivalent resistance of both the supply circuit and the multiplication circuit. A negative impedance converter (Fig. 3b) composed of an operational amplifier A I ' and of resistors Ra,Rb transforms the resistance R M at the output into the resistance R M '=-R M .Ra/Rb at the input if the resistors Ra,Rb are connected as represented in Fig. 3b, and into the resistance R M '=-R M .Rb/Ra if the resistors in Fig. 3b are mutually interchanged. If this interchanging is performed by a control signal P periodically with realisation times of both configurations being equal then the input resistance is averaged to R M,av '=-(Ra/Rb + Rb/Ra).R M /2 . Supposing that in monolithic technology two resistors with equal resistances differing for 1% can be made , it follows from the last expression that the relation R M '=-R M is realizable with an accuracy of 0,01%. At the output O of the circuit SC there flows the supply current I=U L /(R3 + R M ) when the signal P at the input SI is logic 0 ; here by R M the resistance of the multiplication circuit HMC connected to the output O is meant . When the signal P is logic 1 the supply current is I=-U L /(R3 + Rk-R M ) and its absolute value equals the absolute value of the former supply current if it is set Rk = 2R M . With a signal PP appearing at the output of the frequency divider 29 the mutual interchanging of the resistors R1,R2 in the negative impedance converter is controlled. A parasitic current originating from the offset voltage of the operational amplifier A I is conducted to a mass through the resistor R4 . The parasitic current is compensated most completely when the resistances of the resistors R3,R4 are equal. The advantage of the circuit according to the invention exists in that the absolute value of the output voltage of the Hall sensor multiplication circuit integrated in a monolithic technology on a common substrate with the supply circuit is preserved with an accuracy of 0,01% at the polarity reversal of this voltage.

Claims: Supply circuit for a Hall sensor multiplication circuit, characterized in that a load terminal (L1) is connectable through a first resistor (R3), at one hand through a first controlled switch (23) to the first terminal of an adjustable resistor (Rk), and at the other hand through a second controlled switch (24) to the output terminal (O) and through a third controlled switch (26) to the first terminal of a second resistor (R4), whose second terminal is connected to a grounded load terminal (L2), the first terminal of the second resistor (R4) being connectable through a fourth controlled switch (25) to the first terminal of the adjustable resistor (Rk), that the second terminal of the adjustable resistor (R4) is connected to a common terminal of fifth and sixth controlled switches (15, 16), that the second terminal of the fifth controlled switch (15) is connected to the common terminal of seventh and eigth controlled switches (11, 13) and to the first terminal of a third resistor (R1), that the second terminal of the sixth controlled switch (16) is connected to the common terminal of ninth and tenth controlled switches (12, 14) and to the first terminal of a fourth resistor (R2), that the second terminals of the third and fourth resistors (R1, R2) are connected to the output of an operational amplifier (A₁), whose inverting input is connected to the second terminal of the seventh and ninth controlled switches (11, 12) and whose noninverting input is connected to the second terminal of the eigth and tenth controlled switches (13, 14), that the output terminal (O) is connectable through eleventh and twefth controlled switches (17, 18) to the first terminals of the third and fourth resistors (R1, R2, resp.), that the signal input terminal (SI) is connected to the control terminals of the first and third controlled switches (23, 26), and through inverters (27, 28) to the control terminals of the second and fourth controlled switches (24, 25, resp.) and to the input of a frequency divider (29), that the output of the frequency divider (29) is connected to the control terminals of the seventh, tenth, fifth and twelfth controlled switches (11, 14, 15, 18), and that the output of the frequency divider (29) is connected, through an inverter (19) to the control terminal of the eigth controlled switch (13), through an inverter (20) to the control terminal of the ninth controlled switch (12), through an inverter (21) to a control terminal of the eleventh controlled switch (17), and through an inverter (22) to the control terminal of the sixth controlled switch (16). Supply circuit according to claim 1, characterized in that the resistances of the third and fourth resistors (R1, R2) are equal and the resistance of the adjustable resistor (Rk) equals the doubled resistance of the load at the circuit output (O).

Inventors: ROZMAN, MIRO
Applicants: ISKRA STEVCI INDUSTRIJA MERILNE IN UPRAVLJALNE TEHNIKE KRANJ, D.O.O.
Application year: 1989
Main classification: G01R21
IPC codes: G06G7, G01R21