Constant current circuit and constant current generating method
View Patent ↗A constant current circuit and a constant current generating method, wherein when a voltage in substantially no temperature dependence is applied to an element to output a constant current, temperature dependence of the element can be cancelled. A current indicative of first temperature dependence, which is generated by applying a bias voltage in substantially no temperature dependence to a first current setting section, and a current indicative of second temperature dependence, which is generated by applying a bias voltage in substantially no temperature dependence to a second current setting section are added and outputted as a constant current in substantially no temperature dependence. When a bias voltage in substantially no temperature dependence is applied to a current setting section having resistive components to generate currents, even where the resistive components have temperature dependence, the first and second current setting sections having temperature dependence opposite to each other are parallel-connected and bias voltages are applied thereto, after which the generated currents are added together. Consequently, the temperature dependence contained in the individual current setting sections can be cancelled out and hence a constant current in substantially no temperature dependence can be outputted.
1. A constant current circuit comprising:
a first current setting section of which temperature dependence of a path current indicates first temperature dependence; and
a second current setting section connected in parallel with the first current setting section and indicating second temperature dependence corresponding to temperature dependence opposite to the first temperature dependence; and
a bias applying section applying bias voltage in substantially no temperature dependence to a connection point of the first current setting section and the second current setting section,
wherein currents generated by the first current setting section and the second current setting section are added together and the result of addition is outputted through the bias applying section,
either one of the first and second current setting sections includes at least one MOS transistor on a first current path, and other one of the first and second current setting sections is configured so as to have a plurality of resistive elements connected in series on a second current path, and
a gate voltage of the at least one MOS transistor provided with either one of the first and second current setting sections is generated by dividing the bias voltage by the resistive elements,
wherein the bias applying section comprises:
a transistor having a source terminal connected to the connection point; and
an amplifier circuit receiving a reference voltage and the bias voltage at the connection point as input signals, the amplifier circuit adjusting controlling a control terminal of the transistor and adjusting the bias voltage at the connection point to the reference voltage.
2. The constant current circuit according to claim 1 , wherein
the at least one MOS transistor is configured in such a manner that temperature dependence of a drain current thereof is adjusted according to the gate voltage.
3. The constant current circuit according to claim 2 , wherein the first current setting section includes a first MOS transistor, which is one of the plurality of resistive elements, of which a gate voltage is applied in a region indicative of the first temperature dependence, and
the second current setting section includes a second MOS transistor, which is the at least one MOS transistor, of which the gate voltage is applied in a region indicative of the second temperature dependence.
4. The constant current circuit according to claim 3 , wherein the first current setting section includes a plurality of the first MOS transistors, which form the plurality of the resistive elements, connected in series, and
the gate voltage of the second MOS transistor is generated by dividing the bias voltage by the first MOS transistors.