US 4,061,886 A · Dual tone multiple frequency generator

Abstract

A dual-tone multiple frequency signal generator is provided for use with telecommunications systems, data transfer systems and other applications. The tone encoding system utilizes MOS/LSI integrated circuitry on a single chip powered directly by telephone line voltages. An electronic keyboard circuit provides synchronized pulses to decode single-pole, single-throw keyboard switches by row and column. A crystal-controlled oscillator generates a reference frequency which is divided according to the row and column of an activated keyboard switch to obtain two pulse signals having frequencies representative of the activated switch. The outputs of the divider circuitry are fed to programmed logic array which generates two digitally coded signals each representing a sinusoidal waveform. A digital-to-analog ladder network converts the digitally coded signals to continuous sine waves, and an operational amplifier combines the sinusoidal waveforms to provide a dual-tone output. The integrated circuitry also utilizes electronic switches for the common functions of tone transmission, including applying power to the oscillator, disconnecting the audio transmitter and attenuating the input to the receiver. Complementary-symmetry, metal-oxide semi-conductor elements implement the circuitry design with bi-polar transistors on the same chip performing some of the common function switching.

Claims25

Dependent claims

A multiple frequency signal generator on an MOS integrated circuitry chip for providing a dual-tone output signal representative of a selected key on a keyboard connected to said chip, comprising:

keyboard decode means for generating pulse signals representative of said selected key, including means for directing first synchronized pulses to said keyboard, means for receiving second synchronized pulses from said keyboard and means for decoding said first and second synchronized pulses to generate said pulse signals;
means for generating a fixed frequency;
means for dividing said fixed frequency in response to said pulse signals to generate digital signals having frequencies representative of said selected key;
programmed logic array means having an MOS read-only memory matrix for translating said digital signals to digitally coded signals having code values representative of sinusoidal waveforms;
and
conversion means for converting said digitally coded signals to analog sine wave signals having frequencies representative of said selected key;
and
output means for combining said sine wave signals to generate said dual-tone signal on the output of said chip.

5 more elements

A signal generating system for generating a dual tone, multiple frequency signal, comprising:

keyboard means including a plurality of actuable selector keys arranged in rows and columns with electrical inputs and outputs;
scan signal generator means for generating a series of timed pulses sequentially directed to the inputs of said keys;
first decoder means for generating a first pulse signal responsive to said timed pulses and representative of the row of a selected key of said keys;
second decoder means for generating a second pulse signal responsive to said timed pulses and representative of the column of said selected key;
reference oscillator means connected to said scan signal generator means for generating a reference frequency signal;
first divider means connected to said reference oscillator means and said first decoder means for generating a first digital signal by dividing said reference frequency signal by a factor representative of said first pulse signal;
second divider means connected to said reference oscillator means and said second decoder means for generating a second digital signal by dividing said reference frequency signal by a factor representative of said second pulse signal;
programmed logic array means having a memory matrix for generating first and second digital binary coded signals in response to said first and second digital signals from said first and second divider means respectively, said first and second binary coded signals being digital representations of sinusoidal waveforms;
digital-to-analog converter means for converting said first and second digital binary coded signals to first and second analog sinusoidal signals respectively;
and
means for combining said first and second sinusoidal signals to generate said dual tone, multiple frequency signal.

8 more elements

Dependencies are inferred from the claim text.

Dual tone multiple frequency generator

Life of this patent

Dual tone multiple frequency generator

Life of this patent

Abstract

Claims25