Transimpedance amplifier and analog-digital converter circuit

1. A transimpedance amplifier comprising:

a first terminal supplied with a first power supply voltage; and

a second terminal supplied with a second power supply voltage having a potential lower than that of the first power supply voltage,

wherein the transimpedance amplifier outputs a voltage signal that is converted into a binary signal of one of the first power supply voltage and the second power supply voltage, based on an input analog current signal, and

the input analog current signal is a composite current signal of an analog current signal to be measured and an analog reference current signal serving as a reference signal.

2. The transimpedance amplifier according to claim 1 , further comprising a bipolar transistor having a base that receives the input analog current signal.

3. An analog-digital converter circuit comprising:

a photodiode that generates an analog current signal based on a received optical signal;

a digital-analog converter that generates an analog reference current signal from a digital signal;

a transimpedance amplifier that outputs a binalized voltage signal based on a composite current signal of the analog current signal and the analog reference current signal; and

a register that receives a binalized signal output from the transimpedance amplifier.

4. The analog-digital converter circuit according to claim 3 , wherein

the transimpedance amplifier comprises:

a first terminal supplied with a first power supply voltage; and

a second terminal supplied with a second power supply voltage having a potential lower than that of the first power supply voltage, and

the transimpedance amplifier outputs a voltage signal that is converted into a binary signal of one of the first power supply voltage and the second power supply voltage, based on the composite current signal.

5. The analog-digital converter circuit according to claim 3 , wherein the transimpedance amplifier comprises a bipolar transistor having a base that receives the composite current signal.

6. The analog-digital converter circuit according to claim 3 , further comprising a light-emitting diode that generates the optical signal,

wherein the light-emitting diode and the photodiode constitute a photocoupler.

7. The analog-digital converter circuit according to claim 3 , wherein the digital-analog converter is an R-2R ladder type digital-analog converter.

8. An analog-digital converter circuit comprising:

a photodiode that generates an analog current signal based on a received optical signal;

a digital-analog converter that generates an analog reference current signal from a digital signal; and

a transimpedance amplifier that outputs a binalized voltage signal based on a composite current signal of the analog current signal and the analog reference current signal,

wherein the transimpedance amplifier comprises a bipolar transistor having a base that receives the composite current signal.