Active filter circuit of a capacity ground type
AssigneeSony Corporation
InventorFutao Yamaguchi
Life of this patent
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Abstract
An active filter circuit has differential transistors having first conductivity type bipolar transistors and load transistors having second conductivity type bipolar transistors. A connecting node between the differential transistors and the load transistors is driven by a middle electric potential. Voltage dependent characteristics of earth capacitance including parasitic capacitances parasitic to the differential transistors and the load transistors can be kept constant by offsetting the voltage dependent characteristics of the parasitic capacitances. It is thereby possible to make the active filter circuit small in size and the consumed electric power reduced.
Claims4
An active filter circuit constructed of a transconductance variable type differential amplifier circuit, comprising:
- load transistors consisting of first conductivity type transistor, said load transistors supplied with a first reference voltage;
- differential input transistors consisting of second conductivity type bipolar transistors, said differential input transistors supplied with a second reference voltage;
- a ground capacitance consisting of a first parasitic capacitance parasitic between said load transistors and said first reference voltage and a second parasitic capacitance parasitic between said differential input transistors and said second reference voltage;
- wherein a connecting node between said first conductivity type transistor and said second conductivity type transistor to which said parasitic capacitances are parasitic is driven by a voltage equal to one-half the sum of said first and second reference voltages, and a differential output signal is output corresponding to a difference of input signals input to said differential input transistors from said connecting node.
Dependencies are inferred from the claim text.