|
|
Article: Telephony tone generator rings long loops.(Brief Article)
- Article from:
- EDN
- Article date:
- July 8, 1999
- Author:
CopyrightCOPYRIGHT 1999 Reed Business Information, Inc. (US). This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
|
ALTHOUGH RINGING on signal lines is normally undesirable, its a requirement on telephone lines as part of those BORSHT (battery, overvoltage, ringtrip, supervision, hybrid, test) functions. The LT1684 from Linear Technology is a ringtone-generator IC that develops the requisite sine wave as high as [+ or -] 100V, derived from a PWM signal that you supply from a processor or other source. You can easily isolate the signal with simple 100-pF capacitors, thus eliminating the need for optoisolators.
An active multipole filter within the IC extracts the essential cadence, frequency, and amplitude information from your PWM waveform before boosting it via external ...