Browse Prior Art Database

Tone Detection Circuit

IP.com Disclosure Number: IPCOM000041314D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Bonnet, Y: AUTHOR

Abstract

This article describes a tone detection circuit for a line switching network in which a comparison of a narrow band-pass filter's output energy with the total input signal energy determines whether or not a particular tone is present. Fig. 1 shows a tone detection circuit comprising a band-pass filter with cutoff frequencies FOL and FOH, respectively, two RMS-to-DC converters, two comparators COMP 1, COMP 2 and a validity integration circuit providing a protection against false detection due to transient parasitic pulses. As the input signal is here assumed to have the reference value "0 dBm" and both sections (HPF and LPF) of the band-pass filter have a "0 dB" transmission within their bands, the output of both "IN BAND" and "WIDE BAND" RMS-to-DC converters will give a DC voltage equivalent to "O dBm" (in case of a valid tone).

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Tone Detection Circuit

This article describes a tone detection circuit for a line switching network in which a comparison of a narrow band-pass filter's output energy with the total input signal energy determines whether or not a particular tone is present. Fig. 1 shows a tone detection circuit comprising a band-pass filter with cutoff frequencies FOL and FOH, respectively, two RMS-to-DC converters, two comparators COMP 1, COMP 2 and a validity integration circuit providing a protection against false detection due to transient parasitic pulses. As the input signal is here assumed to have the reference value "0 dBm" and both sections (HPF and LPF) of the band-pass filter have a "0 dB" transmission within their bands, the output of both "IN BAND" and "WIDE BAND" RMS-to-DC converters will give a DC voltage equivalent to "O dBm" (in case of a valid tone). Voltage divider R5-R6, which is an integral part of the "WIDE BAND" RMS-to-DC converter, is chosen so that its output will give a DC voltage equivalent to "- 3 dBm" at its middle point. Consequently, two cases may occur. 1. FOL < F INPUT < FOH COMP 1 will have a "0 dBm" DC level on its + input and a "3 dBm" DC level on its - input, and COMP 2 will have the absolute value of the tone on its + input and a reference threshold voltage VREF, corresponding to a - 40 dBm signal, on its - input. COMP1 and COMP2 dotted output will be equal to logical 1, representing "tone present". 2. F INPUT < FOL or F INPUT > FOH COMP1 wil...