US 3,941,942 A · Two of eight tone encoder

Abstract

A two of eight tone encoder utilizing digital techniques to synthesize the dual tones of a Touch Tone telephone operator system is provided. One of sixteen switches from the telephone keyboard selects one of four desired row tones and one of four desired column tones. The two of eight encoder circuit includes, for the row encoding section, a counter which is programmable by the row input signals. The counter output drives a plurality of exclusive OR gates and a one of eight decoder which switches one of eight resistors into a resistive divider network. The exclusive OR gates and the one of eight decoder cooperate to perform an up-down counting function. The eight resistors are chosen in value so that a synthesized stepped sine wave is generated at the output of the resistive divider network, the synthesized stepped sine wave corresponding to the desired selected row frequency. Similar circuitry generates a stepped sine wave corresponding to the desired selected column frequency. The two stepped sine waves are filtered, if desired, and provided as inputs to a summation amplifier, the output of which produces the desired tone having the frequency components for both the selected row input and the selected column input.

Claims10

Dependent claims

An X of Y tone encoder for synthesizing X selected tone signals at an output thereof, X and Y being integers, including clock signal input means for generating a reference input signal, comprising:

programmable counting circuit means for counting a preselected one of a plurality of up-down sequences coupled to said clock signal input means, wherein an up-down sequence is a repetitive sequence of numbers wherein each number is incremented from the previous number until all bits of a number are logical 1's, and then each number is decremented from the previous number until all bits of a number are a logical 0;
digital-to-analog conversion circuit means coupled to said programmable counting circuit means for converting digital output signals from said programmable counting circuit means to X analog signals;
and
a summation amplifier circuit for summing said X analog signals coupled to said digital-to-analog conversion circuit means for producing a single output signal including X selected tone signals.

1 more element

A two-of-eight tone encoder for synthesizing two of eight signals at an output thereof comprising:

first and second programmable counter means coupled to an input signal conductor for each generating a preselected one of four up-down counting sequences at a plurality of outputs thereof, wherein an up-down sequence is a sequence of numbers repetitively incremented until all bits of a number are logical 1's and then decremented until all bits of a number are logical 0's;
first and second decoder circuit means coupled, respectively, to said outputs for each selecting, in an up-down sequence, occurrence of binary combinations of logical levels at said plurality of outputs;
first and second switchable resistive circuit means coupled to, respectively, said first and second decoder circuit means for synthesizing first and second stepped sine wave signals at outputs of said first and second switchable circuit means, respectively, by having various resistor ratios selected, respectively, by said first and second decoder means in response to digital signals at outputs of said first and second decoder circuit means;
and
a summation amplifier circuit for summing said first and second stepped sine wave signals coupled to said outputs of said first and second switching resistive networks.

2 more elements

Dependencies are inferred from the claim text.

Two of eight tone encoder

Life of this patent

Two of eight tone encoder

Life of this patent

Abstract

Claims10