Browse Prior Art Database

Frequency Detection Network

IP.com Disclosure Number: IPCOM000090675D
Original Publication Date: 1969-Jun-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Althauser, WE: AUTHOR [+2]

Abstract

The circuit decodes tone bursts of 500 cps to 2,000 cps. The bursts are transmitted over a communications channel to remote locations as command signals to control the operation of remote equipment. The circuit interpret the tone bursts as logic commands for the equipment being controlled. One circuit is provided for each possible transmitted frequency. Each circuit is selective within + 2% of the nominal frequency to detect the presence or absence of the particular signal frequencies that are transmitted. The detection circuit is symmetrical about the nominal fundamental frequency being detected. To provide the highly accurate and symmetrical detection required, the sinusoidal current through high Q series resonant circuit 2 is measured.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 81% of the total text.

Page 1 of 2

Frequency Detection Network

The circuit decodes tone bursts of 500 cps to 2,000 cps. The bursts are transmitted over a communications channel to remote locations as command signals to control the operation of remote equipment. The circuit interpret the tone bursts as logic commands for the equipment being controlled. One circuit is provided for each possible transmitted frequency. Each circuit is selective within + 2% of the nominal frequency to detect the presence or absence of the particular signal frequencies that are transmitted. The detection circuit is symmetrical about the nominal fundamental frequency being detected. To provide the highly accurate and symmetrical detection required, the sinusoidal current through high Q series resonant circuit 2 is measured. Transistors T1 and T2 form a differential amplifier of low driving and terminating impedance. The low impedance avoids appreciably loading of circuit 2. For accuracy considerations, the input at the base of T1 consists of a square wave voltage at the fundamental frequency to be detected. Since T1 acts as an approximately ideal voltage source, a square wave current flows through resistor 1, but a sine- wave current flows through circuit 2. This then produces a sinusoidal voltage across collector load resistor 3 whose amplitude is a function of the input frequency. The voltage amplitude of the output is large at resonance and rapidly becomes small as the frequency drifts outside the +2% range. This outp...