Constant voltage circuit, constant voltage supply system and constant voltage supply method
An input voltage signal VIN to be inputted to a gate terminal of a PMOS transistor M 1 is converted to a voltage value which was level shifted at the source terminal by an inter-terminal voltage between the gate and source of the PMOS transistor M 1 . This conversion is carried out in accordance with a bias current I 1 flowing from the constant current source IS through the source terminal of the PMOS transistor M 1 . The voltage thus converted is outputted from a source follower circuit through a capacitative element C 1 . A low-pass filter is constituted of the impedance of the PMOS transistor M 1 and the capacitative element C 1 in a signal path extending from the input voltage signal VIN to the source follower circuit.
1. A constant voltage circuit comprising:
an input transistor that receives an input voltage signal supplied by a bandgap reference circuit at a gate terminal;
a constant current source that outputs a bias current with respect to a source terminal of the input transistor, the constant current source being coupled to a current mirror circuit that provides the bandgap reference circuit with a bias current;
a capacitative element having one terminal coupled to a path that couples the input transistor and the constant current source; and
a source follower circuit that receives a voltage signal generated at the one terminal of the capacitative element,
wherein at least one diode is provided in a path that couples the input transistor and the constant current source and leads from the input transistor to the capacitative element.
2. The constant voltage circuit according to claim 1 wherein another terminal of the capacitative element is coupled to one of a source voltage and a ground voltage.
3. The constant voltage circuit according to claim 1 wherein the at least one diode includes a diode-connected transistor.
4. A constant voltage supply system that supplies a predetermined voltage to a later stage circuit, comprising:
a voltage supply unit that supplies an input voltage signal, the voltage supply unit including a bandgap reference circuit;
an input transistor that receives the input voltage signal at a gate terminal;
a constant current source that outputs a bias current with respect to a source terminal of the input transistor, the constant current source being coupled to a current mirror circuit that provides the bandgap reference circuit with a bias current;
a capacitative element having one terminal coupled to a path that couples the input transistor and the constant current source; and
a source follower circuit that receives voltage signal generated at the one terminal of the capacitative element, the source follower circuit being adapted to supply a predetermined voltage to the later stage circuit,
wherein at least one diode is provided in a path that couples the input transistor and the constant current source and leads from the input transistor to the capacitative element.
5. A constant voltage supply method:
inputting an input voltage signal supplied by a bandgap reference circuit to a gate terminal of an input transistor;
outputting a bias current with respect to a source terminal of the input transistor, the bias current being generated based on a current mirror circuit that provides the bandgap reference circuit with the bias current;
converting a level of the input voltage signal by the bias current, in accordance with a conduction control voltage of the input transistor and a forward voltage of a diode provided in a signal path of the bias current; and
providing a low-pass filter characteristic to a signal path when converting the level.
6. The constant voltage supply method according to claim 5 , wherein the conduction control voltage includes an inter-terminal voltage between a gate terminal and a source terminal at a time a drain current flows in a MOS transistor.
7. A constant voltage circuit comprising:
an input transistor that receives an input voltage signal supplied by a bandgap reference circuit at a base terminal;
a constant current source that outputs a bias current with respect to an emitter terminal of the input transistor, the constant current source being coupled to a current mirror circuit that provides the bandgap reference circuit with a bias current;
a capacitative element having one terminal coupled to a path that couples the input transistor and the constant current source; and
an emitter follower circuit that receives a voltage signal generated at the one terminal of the capacitative element,
wherein at least one diode is provided in a path that couples the input transistor and the constant current source and leads from the input transistor to the capacitative element.
8. The constant voltage circuit according to claim 7 wherein another terminal of the capacitative element is coupled to one of a source voltage and a ground voltage.
9. The constant voltage circuit according to claim 7 wherein the at least one diode includes a diode-connected transistor.
10. A constant voltage supply system that supplies a predetermined voltage to a later stage circuit, comprising:
a voltage supply unit that supplies an input voltage signal, the voltage supply unit including a bandgap reference circuit;
an input transistor that receives the input voltage signal at a base terminal;
a constant current source that outputs a bias current with respect to an emitter terminal of the input transistor, the constant current source being coupled to a current mirror circuit that provides the bandgap reference circuit with a bias current;
a capacitative element having one terminal coupled to a path that couples the input transistor and the constant current source; and
an emitter follower circuit that receives a voltage signal generated at the one terminal of the capacitative element, the emitter follower circuit being adapted to supply a predetermined voltage to the later stage circuit,
wherein at least one diode is provided in a path that couples the input transistor and the constant current source and leads from the input transistor to the capacitative element.
11. A constant voltage supply method:
inputting an input voltage signal supplied by a bandgap reference circuit to a base terminal of an input transistor;
outputting a bias current with respect to an emitter terminal of the input transistor, the bias current being generated based on a current mirror circuit that provides the bandgap reference circuit with the bias current;
converting a level of the input voltage signal by the bias current, in accordance with a conduction control voltage of the input transistor and a forward voltage of a diode provided in a signal path of the bias current; and
providing a low-pass filter characteristic to a signal path when converting the level.
12. The constant voltage supply method according to claim 11 , wherein the conduction control voltage includes an inter-terminal voltage between a base terminal and an emitter terminal at a time a collector current flows in a bipolar transistor.
13. The constant voltage circuit according to claim 1 further comprising another capacitative element having one terminal coupled to a source terminal of the source follower circuit.
14. The constant voltage supply system according to claim 4 further comprising another capacitative element having one terminal coupled to a source terminal of the source follower circuit.