Voltage to pulse-width conversion circuit
First Claim
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1. A brightness control circuit for an electronic indicator, comprising:
- an oscillation circuit which generates a reference frequency signal;
a counter receiving said reference frequency signal and producing a digital output signal having a multi-bit digital value corresponding to a count of cycles of said reference frequency signal;
a digital/analog converter receiving said digital output signal and producing an analog output signal having an analog value which corresponds to said multi-bit digital value, said digital/analog converter comprising a decoder for producing a decoded signal from an eight-bit input signal, a plurality of analog switches which are individually selectable according to said decoded signal, and a plurality of voltage-dividing resistors connected to a voltage supply, said voltage-dividing resistors being correspondingly connected to ones of said plurality of analog switches;
means for supplying a selected reference voltage; and
a voltage comparator receiving as inputs and comparing said reference voltage and said analog output signal, and producing a pulse width modulation signal corresponding to the difference between said inputs, said pulse width modulation signal determining a duty cycle ratio for controlling the brightness of the electronic indicator;
whereby said voltage supply is divided by said voltage-dividing resistors to produce said output voltage signal corresponding to said analog value via the selected one of said plurality of analog switches.
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Abstract
A voltage to pulse-width conversion circuit includes a counter which counts a reference frequency signal and produces a multi-bit digital value; a digital/analog converter which converts the digital value into an analog signal; and a voltage comparator which compares an output of the digital/analog converter with a control signal and produces a pulse width modulated output signal which has a predetermined duty cycle ratio.
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Citations
11 Claims
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1. A brightness control circuit for an electronic indicator, comprising:
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an oscillation circuit which generates a reference frequency signal; a counter receiving said reference frequency signal and producing a digital output signal having a multi-bit digital value corresponding to a count of cycles of said reference frequency signal; a digital/analog converter receiving said digital output signal and producing an analog output signal having an analog value which corresponds to said multi-bit digital value, said digital/analog converter comprising a decoder for producing a decoded signal from an eight-bit input signal, a plurality of analog switches which are individually selectable according to said decoded signal, and a plurality of voltage-dividing resistors connected to a voltage supply, said voltage-dividing resistors being correspondingly connected to ones of said plurality of analog switches; means for supplying a selected reference voltage; and a voltage comparator receiving as inputs and comparing said reference voltage and said analog output signal, and producing a pulse width modulation signal corresponding to the difference between said inputs, said pulse width modulation signal determining a duty cycle ratio for controlling the brightness of the electronic indicator;
whereby said voltage supply is divided by said voltage-dividing resistors to produce said output voltage signal corresponding to said analog value via the selected one of said plurality of analog switches. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A brightness control circuit for an electronic indicator, comprising:
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an oscillation circuit which generates a reference frequency signal; a counter receiving said reference frequency signal and producing a digital output signal having a multi-bit digital value corresponding to a count of cycles of said reference frequency signal; a digital/analog converter receiving said digital output signal and producing an analog output signal having an analog value which corresponds to said multi-bit digital value; means for supplying a selected reference voltage; and a voltage comparator receiving as inputs and comparing said reference voltage and said analog output signal, and producing a pulse width modulation signal corresponding to the difference between said inputs; a detection circuit which detects an OFF condition of said means for supplying a selected reference voltage and produces an output detection signal having a relatively high value in response to said OFF condition, and a logical OR gate receiving as inputs said pulse width modulation signal and said detection signal and producing a logical output signal which is a logical sum of said inputs, said logical output signal being supplied to said electronic indicator for determining a duty cycle ratio for controlling brightness of said electronic indicator.
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8. A brightness control circuit for an electronic indicator, comprising:
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an oscillation circuit which generates a reference frequency signal; a counter receiving said reference frequency signal and producing a digital output signal having a multi-bit digital value corresponding to a count of cycles of said reference frequency signal; a digital/analog converter receiving said digital output signal and producing an analog output signal having an analog value which corresponds to said multi-bit digital value; means for supplying a selected reference voltage; and a voltage comparator receiving as inputs and comparing said reference voltage and said analog output signal, and producing a pulse width modulation signal corresponding to the difference between said inputs, said pulse width modulation signal determining a duty cycle ratio for controlling the brightness of the electronic indicator; and a logical OR gate receiving as inputs said pulse width modulation signal and said analog output signal and producing a logical output signal which is a logical sum of said inputs, said logical output signal being supplied to said electronic indicator.
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9. A brightness control circuit for an electronic indicator, comprising:
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an oscillation circuit which generates a reference frequency signal; a counter receiving said reference frequency signal and producing a digital output signal having a multi-bit digital value corresponding to a count of cycles of said reference frequency signal; a digital/analog converter receiving said digital output signal and producing an analog output signal having an analog value which corresponds to said multi-bit digital value; means for supplying a selected reference voltage; and a voltage comparator receiving as inputs and comparing said reference voltage and said analog output signal, and producing a pulse width modulation signal corresponding to the difference between said inputs, said pulse width modulation signal determining a duty cycle ratio for controlling the brightness of the electronic indicator; and an additional circuit which includes a flip-flop circuit and a logical OR gate, said logical OR gate receiving as inputs said pulse width modulation signal and said analog output signal and producing a logical output signal which is a logical sum of said pulse width modulation signal and said analog output signal, said flip-flop circuit receiving as inputs said logical output signal and said reference frequency signal and producing an output signal which corresponds to said pulse width modulation signal to said electronic indicator, said additional circuit providing stability against transient effects and noise in said output signal which corresponds to said pulse width modulation signal. - View Dependent Claims (10, 11)
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Specification