US 4,560,963 AGranted

Analog RC active filter

AssigneeU.S. Philips Corporation

InventorRobin Sharpe

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Abstract

An RC active filter device which is implemented with integrated circuit technology. Each RC filter element of the device has a distributed series resistance and a distributed shunt capacitance. The series resistance is formed by a strip of resistive material which overlies a resistive plate (or substrate) with an intervening insulating layer to form the shunt capacitance. The filter device can be designed to have a pass-band ripple response which is not affected by variation in nominal absolute resistance and capacitance values resulting from process spreads. These variations only stretch or compress the filter response along the frequency axis. The filter device comprises three RC filter elements and an operational amplifier. The RC filter elements nearest the operational amplifier determine a low pass band, while the input filter element prevents high frequency components outside the low pass band being leaked directly to the filter device output.

Claims5

Dependent claims

An analog wave filter device comprising an active device and first and second RC filter elements each providing a series resistance and a shunt capacitance, each filter element having first and second connection points between which its series resistance is defined and a third connection point for the shunt capacitance, the first connection point of the first filter element serving as an input of the filter device, the second connection point of the first filter element being connected to the first connection point of the second filter element, the second connection point of the second filter element being connected to an input of the active device, the third connection point of the first filter element being connected to an output of the active device, and the third connection point of the second filter element being connected to ground, which filter device has an integrated operational amplifier as its active device and has its first and second RC filter elements in integrated distributed form, and which filter device is characterized by comprising a third RC filter element which is of the same distributed form as the first and second filter elements and which has its second connection point connected to the first connection point of the first filter element and its third connection point connected to ground, the first connection point of the third filter element forming the input of the filter device.

Dependencies are inferred from the claim text.