Photoreceiving circuit
View Patent ↗A buffer circuit includes a first transistor (T 1 ) having a base connected to a first power supply, the emitter (E 1 ) and collector (C 1 ) connected as input and output nodes, a second transistor (T 2 ) having a base connected to the first power supply, a first constant current circuit using a difference between outgoing current from E 1 and an input current at the current signal input node as a constant current, and determining outgoing current from the emitter of T 2 equal to the constant current; and a first mirror circuit equalizing first and second collector currents with a third transistor (T 3 ) with C 1 and a fourth transistor (T 4 ) with a collector connected to a collector of T 2 , a first operating point voltage is provided to the current signal output node between T 3 and T 1 , and a second operating point voltage based on the first operating point voltage between T 4 and T 2.
1. A photoreceiving circuit comprising:
a buffer circuit that comprises:
a first transistor having a base connected to a first power supply, an emitter as a current signal input node, and a collector as a current signal output node;
a second transistor having a base connected to the first power supply;
a first constant current circuit using a difference between outgoing current from the emitter of the first transistor and an input current at the current signal input node as a constant current, and determining outgoing current from the emitter of the second transistor as a current same as the constant current; and
a first mirror circuit that makes a collector current of the first transistor equal to a collector current of the second transistor, the first mirror circuit having a third transistor with a collector connected to the collector of the first transistor and a fourth transistor with a collector connected to a collector of the second transistor, the buffer circuit being configured such that a first operating point voltage is provided to the current signal output node between the third transistor and the first transistor and a second operating point voltage based on the first operating point voltage is provided to a node between the fourth transistor and the second transistor;
a photoreceiving device connected to the current signal input node; and
a current-voltage conversion circuit connected to the current signal output node.
2. The photoreceiving circuit according to claim 1 , wherein the first mirror circuit includes a fifth transistor as a reference.
3. The photoreceiving circuit according to claim 2 , further comprising a sixth transistor to provide the second operating point voltage for a node between the fourth transistor and the second transistor.
4. The photoreceiving circuit according to claim 3 , further comprising a seventh transistor having an emitter connected to a base of the sixth transistor,
wherein a voltage provided to the node between the fourth transistor and the second transistor and a voltage provided to the current signal output node are determined as approximately equal.
5. The photoreceiving circuit according to claim 1 , further comprising a second mirror circuit to flow therethrough a differential current between the currents in the first constant current circuit and the first mirror circuit.
6. The photoreceiving circuit according to claim 5 , further comprising a sixth transistor to provide the second operating point voltage for a node between the fourth transistor and the second transistor.
7. The photoreceiving circuit according to claim 6 , further comprising a seventh transistor having an emitter connected to a base of the sixth transistor,
wherein a voltage provided to the node between the fourth transistor and the second transistor and a voltage provided to the current signal output node are determined as approximately equal.
8. The photoreceiving circuit according to claim 1 , further comprising a sixth transistor to provide the second operating point voltage for a node between the fourth transistor and the second transistor.
9. The photoreceiving circuit according to claim 8 , further comprising a seventh transistor having an emitter connected to a base of the sixth transistor,
wherein a voltage provided to the node between the fourth transistor and the second transistor and a voltage provided to the current signal output node are determined as approximately equal.
10. A photoreceiving circuit comprising:
a photoreceiving device connected to the current signal input node;
a current-voltage conversion circuit connected to the current signal output node; and
a first buffer circuit provided on an input side of the current-voltage conversion circuit, and a second buffer circuit provided on a reference side,
wherein each of the first buffer circuit and the second buffer circuit comprises:
a first transistor having a base connected to a first power supply, an emitter as a current signal input node, and a collector as a current signal output node;
a second transistor having a base connected to the first power supply;
a first constant current circuit using a difference between outgoing current from the emitter of the first transistor and an input current at the current signal input node as a constant current, and determining outgoing current from the emitter of the second transistor as a current same as the constant current; and
a first mirror circuit that makes a collector current of the first transistor equal to a collector current of the second transistor, the first mirror circuit has a third transistor with a collector connected to the collector of the first transistor and a fourth transistor with a collector connected to a collector of the second transistor,
a first operating point voltage is provided to the current signal output node between the third transistor and the first transistor, and
a second operating point voltage based on the first operating point voltage is provided to a node between the fourth transistor and the second transistor.
11. The photoreceiving circuit according to claim 10 , wherein the first mirror circuit includes a fifth transistor as a reference.
12. The photoreceiving circuit according to claim 11 , further comprising a sixth transistor to provide the second operating point voltage for a node between the fourth transistor and the second transistor.
13. The photoreceiving circuit according to claim 12 , further comprising a seventh transistor having an emitter connected to a base of the sixth transistor,
wherein a voltage provided to the node between the fourth transistor and the second transistor and a voltage provided to the current signal output node are determined as approximately equal.
14. The photoreceiving circuit according to claim 10 , further comprising a second mirror circuit to flow therethrough a differential current between the currents in the first constant current circuit and the first mirror circuit.
15. The photoreceiving circuit according to claim 14 , further comprising a sixth transistor to provide the second operating point voltage for a node between the fourth transistor and the second transistor.
16. The photoreceiving circuit according to claim 15 , further comprising a seventh transistor having an emitter connected to a base of the sixth transistor,
wherein a voltage provided to the node between the fourth transistor and the second transistor and a voltage provided to the current signal output node are determined as approximately equal.
17. The photoreceiving circuit according to claim 10 , further comprising a sixth transistor to provide the second operating point voltage for a node between the fourth transistor and the second transistor.
18. The photoreceiving circuit according to claim 17 , further comprising a seventh transistor having an emitter connected to a base of the sixth transistor,
wherein a voltage provided to the node between the fourth transistor and the second transistor and a voltage provided to the current signal output node are determined as approximately equal.
19. A photoreceiving circuit comprising:
a first transistor having a base connected to a first power supply and provided between a photoreceiving device and a current-voltage conversion circuit;
a second transistor having a base connected to the first power supply;
a first constant current circuit using a difference between outgoing current from the emitter of the first transistor and an input current at the current signal input node as a constant current, and determining outgoing current from the emitter of the second transistor as a current same as the constant current;
a first mirror circuit that makes a collector current of the first transistor equal to a collector current of the second transistor; and
a second constant current circuit functioning as a reference current of the first mirror circuit,
wherein the first mirror circuit has a third transistor with a collector connected to the collector of the first transistor and a fourth transistor with a collector connected to a collector of the second transistor,
a first operating point voltage is provided to the current signal output node between the third transistor and the first transistor, and
a second operating point voltage based on the first operating point voltage is provided to a node between the fourth transistor and the second transistor.