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Browse Prior Art Database

Bandpass/Stop Filter

IP.com Disclosure Number: IPCOM000081892D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Gianopulos, W: AUTHOR [+2]

Abstract

This filter provides highly selective discrimination for or against a particular input frequency. The example given is a low-pass filter.

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Bandpass/Stop Filter

This filter provides highly selective discrimination for or against a particular input frequency. The example given is a low-pass filter.

The input on line 110 is fed to a very low frequency (noise) blocking filter 12, the output of which on line 14 is fed to an operational amplifier 16 to square up the wave. The quiescent output of amplifier 16 is negative.

At very low-input frequencies, the Vc1 and Vc2 would follow the input, switching the Schmitt trigger on and off. These low frequencies are blocked by noise filter 12.

When the input frequency is high enough, the double integration afforded by the two cascaded RC circuits R3, C1 and R5 C2 (including the input impedance of the Schmitt trigger, if significant) prevents the charge on C2, Vc2, from rising high enough to intercept the upper switching level of the Schmitt trigger, so that the trigger output will stay up. However, when an input signal of a frequency above a certain value, F2, is applied to the input 10, the cascaded integrating stages allow Vc2 to rise toward +Vcc, intercepting the upper switching level of the Schmitt trigger, turning it off; that is, to its lower level output. F2 is determined by the values of the two integrating networks.

The output of the Schmitt trigger on line 24 conditions an analog gate 25, passing or blocking the original analog signal on line 26. Accordingly, the output on line 27 is the original input wave form switched on or off in a highly selective m...