BIQUAD TYPE CONSTANT CURRENT ACTIVE FILTER

摘要

PURPOSE:To obtain stability against variations of temperature characteristics and a source voltage by constituting various biquad type filter circuits and obtaining desired filter characteristics, and outputting a current to be supplied whose current is proportional to a temperature voltage. CONSTITUTION:Currents Ii and Ie supplied to various integrators 10-1n are so set by constant current circuits 20 and 30 that Ii=VT/Ri and Ie=VT/Re. The constant current circuit 20 consists of transistors (TR) Q21-Q31 and resistances R1, R2, and (r). A current I0 flowing from a constant current terminal T has a constant current value. In this circuit 20, TRs Q23 and Q24 constitute a differential amplifier circuit and a TR Q27 constitutes a negative feedback circuit. Therefore, base voltages V1 and V2 of the TRs Q23 have invariably the same values regardless of the source voltage Vcc.