Voltage generating circuit
A voltage generating circuit, in which the influence of offset of an amplifier on an output voltage is reduced, has first and second bipolar transistors (Q 1 , Q 2 ) having emitter terminals at the same electric potential. A base terminal of Q 1 is disposed on a collector side of Q 2 . A first resistance element connects the collector side of Q 2 with the base side of Q 2 ; and a second resistance element (R 1 ) connects a collector side of Q 1 to R 2 . A third resistance element (R 3 ) connects a base terminal of Q 2 with the electric potential of the emitter terminals. An amplifier (A 1 ) outputs a voltage based on a voltage difference between the collector sides of Q 1 and Q 2 ; and a voltage-current converting section (MP 1 , MP 2 ) converts amplifier output into a current supplied to the connection node of R 1 and R 2 . A voltage is then output on the basis of the generated current.
1. A voltage generating circuit comprising:
a current generating section that generates a current obtained by adding a current based on a voltage difference between base-emitter voltages of two bipolar transistors having different emitter areas and a current based on a forward voltage of a PN junction, and
an output section that converts an input current into a voltage and outputs the converted voltage,
wherein the current generating section includes:
a first bipolar transistor that includes an emitter terminal connected to a first node, a base terminal connected to a second node, and a first collector terminal;
a second bipolar transistor that has an emitter area larger than an emitter area of the first bipolar transistor, and includes an emitter terminal connected to the first node, a base terminal connected to the first collector terminal of the first bipolar transistor and a second collector terminal;
a first resistance element that is connected to the first collector terminal of the first bipolar transistor at one end thereof and is connected to the second node at the other end thereof;
a second resistance element that is connected to the second collector terminal of the second bipolar transistor at one end thereof and is connected to the second node at the other end thereof;
a third resistance element that is connected to the second node at one end thereof and is connected to a first electric potential node at the other end thereof;
an amplifier that receives, as inputs, a voltage on the first collector terminal of the first bipolar transistor and a voltage on the second collector terminal of the second bipolar transistor and outputs a voltage based on a voltage difference between the two input voltages; and
a voltage-current converting section that receives, as an input, the output voltage of the amplifier, converts the received voltage into currents and supplies the converted currents to the second node and to the output section,
wherein the output section includes a fourth resistance element which is supplied one of the converted currents and outputs the converted voltage based on the one of the converted currents, and
wherein a resistance value of the third resistance element is larger than a resistance value of the fourth resistance element.
2. The voltage generating circuit according to claim 1 ,
wherein the current generating section includes a fifth resistance element connected between the first node and the first electric potential node.
3. The voltage generating circuit according to claim 1 ,
wherein the fourth resistance element is connected to the first electric potential node at one end thereof and receives the one of the converted currents at the other end thereof.
4. The voltage generating circuit according to claim 1 ,
wherein the first bipolar transistor and the second bipolar transistor are NPN bipolar transistors.
5. The voltage generating circuit according to claim 1 , further comprising:
a correcting circuit that generates a correcting current based on a difference between the converted voltage generated by the output section and the forward voltage of the PN junction and feeds back the correcting current to the current generating section.
6. The voltage generating circuit according to claim 5 ,
wherein the correcting circuit includes:
a third bipolar transistor that is connected to the first electric potential node through a fifth resistance element at an emitter terminal thereof and is connected to an output side of the voltage generating section at a base terminal thereof; and
a current mirror section that outputs a current based on a current that flows in a third collector terminal of the third bipolar transistor.
7. The voltage generating circuit according to claim 6 ,
wherein the emitter terminal of the first bipolar transistor is connected to the first electric potential node through a sixth resistance element, and
wherein the correcting current is fed back to the emitter terminal of the first bipolar transistor.
8. The voltage generating circuit according to claim 6 ,
wherein the correcting circuit further includes a buffer circuit that receives the converted voltage of the output section as an input and buffers the received converted voltage which is then output to the base terminal of the third bipolar transistor.