Title:
DIAL TONE DETECTOR
Document Type and Number:
Japanese Patent JPS6471292
Kind Code:
A
Abstract:
PURPOSE: To minimize the number of interface pins by providing a circuit for inputting all signals and outputting a code corresponding to a detected multifrequency call originating tone (DTMF) signal and a signal showing 'presence of monitor signal'. CONSTITUTION: A DTMF and a monitor tone supplied to an input terminal 1 are inputted through an amplifier 2, filter 3 and AGC circuit 4 to a high-pass filter group and a low-pass filter group 5. An output from the filter group 5 is supplied to a Schmitt trigger circuit 6, converted into a rectangular wave and supplied to a DTMF detector, code converter and latch circuit 7 later. When a suitable DTMF frequency is found, a digital code signal corresponding to the frequency of an input signal is supplied through a shift register 8 to an output terminal 9. A steering circuit 11 outputs a display signal showing the presence of DTMF to an EST terminal 11.
Inventors:
MEIBUIN JIEI ROBAATSU
FURANKU DEIA
FURANKU DEIA
Application Number:
JP20100888A
Publication Date:
March 16, 1989
Filing Date:
August 09, 1988
Export Citation:
Assignee:
MITEL CORP
International Classes:
H04Q1/444; H04Q1/45; H04Q1/446; H04Q1/453; (IPC1-7): H04Q1/446; H04Q1/45
Domestic Patent References:
| JPS556941A | 1980-01-18 | |||
| JP44029409A | ||||
| JPS5534508A | 1980-03-11 | |||
| JPS5537649A | 1980-03-15 | |||
| JPS6111786U | 1986-01-23 | |||
| JPS5534525A | 1980-03-11 | |||
| JPS5486210A | 1979-07-09 | |||
| JP44032087A |
Attorney, Agent or Firm:
Aoyama Aoi