Kabushiki Kaisha Toshiba

Tadashi Nukui

Ken Tanabe

An offset cancellation circuit of this invention includes operational amplifiers 11, 12 having fully differential outputs and common mode output, and comprises an adder 15 supplied with one Vo.sup.+ 1 of the fully-differential outputs of the operational amplifier 11 and one Vo.sup.+ 2 of the fully-differential outputs of the operational amplifier 12 to add them to output added result, an adder 16 supplied with the other Vo.sup.- 1 of the fully-differential outputs of the operational amplifier 11 and the other Vo.sup.- 2 of the fully-differential outputs of the operational amplifier 12 to add them to output added result, an adder 13 supplied with common mode output Vcm1 of the operational amplifier 11 and common mode output Vcm2 of the operational amplifier 12 to add them to output added result, and a multiplier 14 for multiplying an output of the adder 13 by 1/2 to output it. Thus, it is possible to eliminate influence of error resulting from offset quantities existing in respective common mode output potentials in plural operational amplifiers having fully-differential outputs.

Offset cancellation circuit

A power source device including, a primary reference voltage generating device having a positive power source terminal connected to receive one of ground potential and a DC positive voltage and a negative power source terminal connected to receive a primary DC negative voltage for generating a primary reference voltage, a reference voltage generating device having a positive power source terminal connected to receive the DC positive voltage and a negative power source terminal connected to receive the primary reference voltage for generating a reference voltage, a positive voltage generating device for obtaining a difference between the reference voltage and the primary reference voltage and amplifying the difference to generate the DC positive voltage, a negative voltage generating device for inverting amplifying the DC positive voltage to generate a negative DC voltage, and an integrated circuit having a positive power source terminal connected to receive the DC positive voltage and a negative power source terminal connected to receive the DC negative voltage. The integrated circuit and the reference voltage generating device are integrated and formed on a n-type substrate, and the negative power source terminal of the integrated circuit is isolated from the negative power source terminal of the reference voltage generating device.

Power source device for watthour meter

A power calculating device including a control signal generating unit for generating a control signal. The control signal determines a power calculating period and an imbalance compensation period. The device also includes an input voltage changeover unit for changing over between a first voltage corresponding to a voltage of a system under measurement and a constant voltage under the control of the control signal to generate a second voltage, which is the first voltage during the power calculating period and the constant voltage during the imbalance compensation period. The device further includes a Hall element member for generating a third voltage corresponding to a product of the second voltage and a magnetic density generated by a magnetic field applied to the Hall element member. The device also includes an imbalance detecting unit for generating an offset compensation signal based on the third voltage, and a variable resistor connected to the Hall element member. The resistance value thereof is changed by the offset compensation signal, whereby an imbalance voltage of the Hall element member is compensated.

Power calculating device

A voltage to frequency converter including a first selector for receiving an input voltage and for generating an input current based on the control signal. The input current is proportional to the input voltage or an inverse polarity input voltage when the control signal designates plus, or minus integration period, respectively. The converter further includes a second selector for generating a reference current such that the reference current is on/off controlled based on the selection signal and a polarity of the reference current is determined by the control signal, and an integrator for integrating a resultant current of the input current and the reference current to obtain an integrated voltage. The integrator integrates the resultant current complementarily in a forward or in a reverse direction. The converter also includes a comparator for comparing the integrated voltage and a reference voltage to generate a comparison output signal, a selection signal generator for generating the selection signal based on the comparison output signal and the control signal, a control signal generator for generating the control signal based on the selection signal, and an output circuit for generating the selection signal as an output signal of the converter having a frequency corresponding to the input voltage.

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Kanagawa, Japan

Tadashi Nukui