Patent ID: 8842855
Filing Date: 2014-09-23
Classification: H03G

Abstract:
1. A sound volume control circuit that controls sound volume by digitally changing an output voltage comprising: a first operational amplifier including: an inverting input; a non-inverting input connected to a voltage source of a reference voltage; and an output that outputs the output voltage; a variable resistor circuit that is connected between the output and the inverting input, and has a plurality of resistance values; an R-2R ladder circuit that is connected between a voltage source of an input voltage and the inverting input, and changes the magnitude of electric current flowing to the variable resistor circuit, the R-2R ladder circuit including: a control circuit that controls the variable resistor circuit and the R-2R ladder circuit, wherein when changing a resistance value of the variable resistor circuit from a first resistance value to a second resistance value, so as to change the output voltage in a step size where a difference between the output voltage corresponding to the first resistance value and the output voltage corresponding the second resistance value is further segmented, the control circuit changes the magnitude of the electric current flowing to the variable resistor circuit by use of the R-2R ladder circuit, and wherein each of the plurality of the first switches further has a state of being connected to neither the inverting input nor the voltage source of the reference voltage, and in a case of muting, the control circuit changes the resistance value of the variable resistor circuit to a minimum value, switches each of the plurality of the first switches to the state of being connected to neither the inverting input nor the voltage source of the reference voltage, and turns oil the second switch.