US 5,398,031 A · DTMF signal generating circuit

Abstract

A DTMF signal generating circuit for producing output of a selection signal having a frequency corresponding to a signal entered from push buttons. A high frequency oscillation signal output from an oscillatory circuit are delivered to both a first frequency dividing circuit for dividing high frequency signals by a first dividing ratio and a second frequency dividing circuit for dividing high frequency signals by a second dividing ratio, thereby producing two kinds of divided signals each of which has its own predetermined frequency. A fractional frequency division is then accomplished by switching from an output of a first frequency dividing circuit to an output of a second frequency dividing circuit at a predetermined timing. The signals output form the switch are then counted by a ROM address counter, producing an output of an address value signal. The address value signal is then delivered to a sine wave output ROM in which peak values in response to a predetermined sine waveform are preliminary stored in the order of address value, so that 32 digital data corresponding to the input address values are output. Concurrently, a switching rate generator of a frequency dividing circuit supplies a switching timing signal, which is determined by both an address value signal delivered from the ROM address counter and a dividing ratio signal entered from the key input control circuit, to a key input control circuit, thereby generating DTMF signals highly similar to the standard DTMF frequency.

Claims9

Dependent claims

A DTMF signal generating circuit for producing an output of a selection signal which corresponds to a signal entered from pushbuttons, said circuit comprising:

(a) an oscillatory circuit for generating pulse signals having a predetermined high frequency;
(b) a first frequency dividing circuit for dividing pulse signals which are delivered from said oscillatory circuit by a first dividing ratio;
(c) a second frequency dividing circuit, which is connected in parallel with said first frequency dividing circuit, for dividing said pulse signals which are delivered from said oscillatory circuit by a second dividing ratio;
(d) a switch for switching from an output of said first frequency dividing circuit to an output of said second frequency dividing circuit at a switching timing;
(e) a ROM address counter for counting the signal output from said switch and resetting a counted value each time it amounts to a prescribed value, thereby producing an output of an address value signal;
(f) a sine wave output ROM for producing an output of digital data which represents a predetermined sine waveform on the basis of said address value signal delivered from said ROM address counter;
(g) a key input control circuit for determining a dividing ratio in response to a signal entered from the pushbuttons;
and
(h) a switching rate generator responsive to the ROM address counter at the key input control circuit for generating the switching timing for the switch, wherein the switching timing is determined in accordance with the address value signal from the ROM address counter and the dividing ratio signal from the key input control circuit.

6 more elements

A DTMF signal generating circuit for producing an output of a selection signal which corresponds to a signal entered from pushbuttons, said circuit comprising:

(a) an oscillatory circuit for generating pulse signals having a predetermined high frequency;
(b) a one-tenth frequency divider for dividing pulse signals which are delivered from said oscillatory circuit into pulse signals having one tenth the predetermined high frequency;
(c) a first frequency dividing circuit for dividing pulse signals which are delivered from said one-tenth frequency divider by a first dividing ratio;
(d) a second frequency dividing circuit, which is connected in parallel with said first frequency dividing circuit, for dividing pulse signals output from said one-tenth frequency divider by a second dividing ratio;
(e) a switch for switching from an output of said first frequency dividing circuit to an output of said second frequency dividing circuit at a switching timing;
(f) a ROM address counter for counting said signal output from said switch and resetting a counted value each time it amounts to a prescribed value, thereby producing a digital output of an address value signal;
(g) a sine wave output ROM for producing an output of digital data which represents a predetermined sine waveform on the basis of said address value signal input from said ROM address counter;
(h) a digital/analog converter for converting the digital output of the ROM address counter into an analog signal;
(i) a key input control circuit for determining a dividing ratio signal in response to a signal entered from the pushbuttons;
and
(j) a switching rate generator responsive to the ROM address counter and the key input control circuit for generating the switching timing for the switch, wherein the switching timing is determined in accordance with the address value signal from the ROM address counter and the dividing ratio signal form the key input control circuit.

8 more elements

A DTMF signal generating circuit for producing an output of a selection signal which corresponds to a signal entered from push buttons, said circuit comprising:

(a) an oscillatory circuit for generating pulse signals having a predetermined high frequency range;
(b) a first frequency dividing circuit for dividing pulse signals which are delivered from said oscillatory circuit by a first dividing ratio;
(c) a second frequency dividing circuit, which is connected in parallel with said first frequency dividing circuit, for dividing said pulse signals which are delivered from said oscillatory circuit by a second dividing ratio;
(d) a switch for switching from an output from said first frequency dividing circuit to an output of said second frequency dividing circuit at a switching timing;
(e) a ROM address counter for counting the signal output from said switch and resetting a counted value each time it amounts to a prescribed value, thereby producing an output of an address value signal;
(f) a sine wave output ROM for producing an output of digital data which represents a predetermined sine waveform on the basis of said address value signal delivered from said ROM address counter;
(g) a key input control circuit for determining a dividing ratio in response to a signal entered from the pushbuttons;
and
(h) a switching rate generator responsive to the ROM address counter and the key input control circuit for generating the switching timing for the switch, wherein the switching timing is determined in accordance with the address value signal from the ROM address counter and the dividing ratio signal from the key input control circuit;
wherein a ROM address signal generator is disposed between said switch and said ROM address counter so as to delay the output signal of the switch.

7 more elements

Dependencies are inferred from the claim text.

DTMF signal generating circuit

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DTMF signal generating circuit

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Abstract

Claims9