Optical signal detection circuit and optical receiver
An optical signal detection circuit ( 10 ) includes an amplification circuit ( 11 ) that differentially amplifies an electrical signal (Tout) corresponding to the pulse train of an optical signal (Pin) and outputs a differential output signal (Aout), and a comparator ( 12 ) that compares the voltage value of the positive-phase signal of the differential output signal (Aout) with the voltage value of the negative-phase signal and outputs a pulsed comparison output signal (Cout) corresponding to the comparison result. The amplification circuit ( 11 ) includes a current addition circuit ( 11 E) that adjusts a DC load current to generate a positive-phase signal (Aout+) and a negative-phase signal (Aout−) of the differential output signal (Aout) in accordance with an adjusted voltage value from an external adjusted voltage source (Vadj) and adjusts the DC bias of the positive-phase signal (Aout+) and the DC bias of the negative-phase signal (Aout−).
1. An optical signal detection circuit comprising:
an amplification circuit that differentially amplifies a positive-phase signal and a negative-phase signal of an electrical signal including pulses corresponding to a pulse train of an optical signal and outputs a differential output signal;
a comparator that compares a voltage value of the positive-phase signal of the differential output signal with a voltage value of the negative-phase signal and outputs a pulsed comparison output signal corresponding to a comparison result; and
a holding circuit that outputs an optical signal detection signal representing presence/absence of input of the optical signal based on the pulsed comparison output signal,
said amplification circuit comprising:
first and second load resistors that have one-terminal sides connected to a power supply potential and generate the positive-phase signal and the negative-phase signal of the differential output signal, respectively; and
a current addition circuit that adjusts a DC load current flowing to at least one of said first and second load resistors in accordance with an adjusted voltage value from an external adjusted voltage source and adjusts a difference between a DC bias of the positive-phase signal of the differential output signal and a DC bias of the negative-phase signal,
wherein said current addition circuit comprises a current source that is connected to the other terminal of one of said first and second load resistors and has a current value to be controlled in accordance with the adjusted voltage value.
2. An optical signal detection circuit according to claim 1 , wherein said current addition circuit comprises:
a first transistor having a first input/output terminal connected to the other terminal of one of said first and second load resistors and a control terminal receiving the adjusted voltage value;
a second transistor that has a first input/output terminal connected to the other terminal of the other of said first and second load resistors, a control terminal receiving a predetermined voltage value, and a second input/output terminal connected to a second input/output terminal of said first transistor, and forms a differential pair with said first transistor; and
a constant current source connected to a node of the second input/output terminal of said first transistor and the second input/output terminal of said second transistor.
3. An optical signal detection circuit according to claim 1 , wherein said holding circuit comprises:
an analog holding circuit that comprises a holding capacitor to be changed by the pulsed comparison output signal and a discharging resistor connected in parallel to said holding capacitor and removes charges held in said holding capacitor by said discharging resistor, thereby outputting a holding output signal that changes in accordance with the presence/absence of input of the optical signal; and
an output buffer that shapes the holding output signal into a digital logic signal and outputs the optical signal detection signal.
4. An optical signal detection circuit according to claim 3 , wherein said output buffer comprises a Schmitt trigger inverter that shapes, based on a hysteresis characteristic, the holding output signal obtained by said analog holding circuit and outputs the holding output signal.
5. An optical signal detection circuit according to claim 1 , wherein said holding circuit comprises a latch circuit that latches the pulsed comparison output signal and outputs the optical signal detection signal.
6. An optical signal detection circuit according to claim 1 , wherein said amplification circuit further comprises:
a first-stage amplification circuit that differentially amplifies the positive-phase signal and the negative-phase signal of the electrical signal and outputs a first-stage output signal;
an impedance adjustment circuit that has an output impedance lower than the output impedance of said first-stage amplification circuit and outputs the first-stage output signal from said first-stage amplification circuit;
a next-stage bias circuit that is AC-coupled to said impedance adjustment circuit by a coupling capacitor, gives a DC bias to each of a positive-phase signal and a negative-phase signal of the first-stage output signal input via the coupling capacitor, and outputs the positive-phase signal and the negative-phase signal; and
a next-stage amplification circuit that differentially amplifies the positive-phase signal and the negative-phase signal of the first-stage output signal, which are DC-biased by the next-stage bias circuit, and outputs the differential output signal,
said next-stage amplification circuit comprising said first and second load resistors that generate the positive-phase signal and the negative-phase signal of the differential output signal, respectively.
7. An optical receiver comprising:
a photoelectric conversion element that photoelectrically converts an optical signal formed from a pulse train and outputs a photocurrent signal;
a transimpedance amplifier that amplifies the photocurrent signal and outputs an electrical signal including pulses corresponding to the pulse train;
a limiting amplifier that amplifies the electrical signal and outputs a reception output including pulses having a predetermined amplitude; and
an optical signal detection circuit that detects presence/absence of input of the optical signal based on the electrical signal,
said optical signal detection circuit comprising:
an amplification circuit that differentially amplifies a positive-phase signal and a negative-phase signal of the electrical signal and outputs a differential output signal;
a comparator that compares a voltage value of the positive-phase signal of the differential output signal with a voltage value of the negative-phase signal and outputs a pulsed comparison output signal corresponding to a comparison result; and
a holding circuit that outputs an optical signal detection signal representing the presence/absence of input of the optical signal based on the pulsed comparison output signal, and
said amplification circuit comprising:
first and second load resistors that have one-terminal sides connected to a power supply potential and generate the positive-phase signal and the negative-phase signal of the differential output signal, respectively; and
a current addition circuit that adjusts a DC load current flowing to at least one of said first and second load resistors in accordance with an adjusted voltage value from an external adjusted voltage source and adjusts a difference between a DC bias of the positive-phase signal of the differential output signal and a DC bias of the negative-phase signal,
wherein said current addition circuit comprises a current source that is connected to the other terminal of one of said first and second load resistors and has a current value to be controlled in accordance with the adjusted voltage value.
8. An optical signal detection circuit comprising:
an amplification circuit that differentially amplifies a positive-phase signal and a negative-phase signal of an electrical signal including pulses corresponding to a pulse train of an optical signal and outputs a differential output signal;
a comparator that compares a voltage value of the positive-phase signal of the differential output signal with a voltage value of the negative-phase signal and outputs a pulsed comparison output signal corresponding to a comparison result; and
a holding circuit that outputs an optical signal detection signal representing presence/absence of input of the optical signal based on the pulsed comparison output signal,
said amplification circuit comprising:
first and second load resistors that have one-terminal sides connected to a power supply potential and generate the positive-phase signal and the negative-phase signal of the differential output signal, respectively; and
a current addition circuit that adjusts a DC load current flowing to at least one of said first and second load resistors in accordance with an adjusted voltage value from an external adjusted voltage source and adjusts a difference between a DC bias of the positive-phase signal of the differential output signal and a DC bias of the negative-phase signal, wherein said holding circuit comprises:
an analog holding circuit that comprises a holding capacitor to be changed by the pulsed comparison output signal and a discharging resistor connected in parallel to said holding capacitor and removes charges held in said holding capacitor by said discharging resistor, thereby outputting a holding output signal that changes in accordance with the presence/absence of input of the optical signal; and
an output buffer that shapes the holding output signal into a digital logic signal and outputs the optical signal detection signal.
9. An optical signal detection circuit according to claim 8 , wherein said current addition circuit comprises:
a first transistor having a first input/output terminal connected to the other terminal of one of said first and second load resistors and a control terminal receiving the adjusted voltage value;
a second transistor that has a first input/output terminal connected to the other terminal of the other of said first and second load resistors, a control terminal receiving a predetermined voltage value, and a second input/output terminal connected to a second input/output terminal of said first transistor, and forms a differential pair with said first transistor; and
a constant current source connected to a node of the second input/output terminal of said first transistor and the second input/output terminal of said second transistor.
10. An optical signal detection circuit according to claim 8 , wherein said output buffer comprises a Schmitt trigger inverter that shapes, based on a hysteresis characteristic, the holding output signal obtained by said analog holding circuit and outputs the holding output signal.
11. An optical signal detection circuit according to claim 8 , wherein said holding circuit comprises a latch circuit that latches the pulsed comparison output signal and outputs the optical signal detection signal.
12. An optical signal detection circuit according to claim 8 , wherein said amplification circuit further comprises:
a first-stage amplification circuit that differentially amplifies the positive-phase signal and the negative-phase signal of the electrical signal and outputs a first-stage output signal;
an impedance adjustment circuit that has an output impedance lower than the output impedance of said first-stage amplification circuit and outputs the first-stage output signal from said first-stage amplification circuit;
a next-stage bias circuit that is AC-coupled to said impedance adjustment circuit by a coupling capacitor, gives a DC bias to each of a positive-phase signal and a negative-phase signal of the first-stage output signal input via the coupling capacitor, and outputs the positive-phase signal and the negative-phase signal; and
a next-stage amplification circuit that differentially amplifies the positive-phase signal and the negative-phase signal of the first-stage output signal, which are DC-biased by the next-stage bias circuit, and outputs the differential output signal,
said next-stage amplification circuit comprising said first and second load resistors that generate the positive-phase signal and the negative-phase signal of the differential output signal, respectively.
13. An optical receiver comprising:
a photoelectric conversion element that photoelectrically converts an optical signal formed from a pulse train and outputs a photocurrent signal;
a transimpedance amplifier that amplifies the photocurrent signal and outputs an electrical signal including pulses corresponding to the pulse train;
a limiting amplifier that amplifies the electrical signal and outputs a reception output including pulses having a predetermined amplitude; and
an optical signal detection circuit that detects presence/absence of input of the optical signal based on the electrical signal,
said optical signal detection circuit comprising:
an amplification circuit that differentially amplifies a positive-phase signal and a negative-phase signal of the electrical signal and outputs a differential output signal;
a comparator that compares a voltage value of the positive-phase signal of the differential output signal with a voltage value of the negative-phase signal and outputs a pulsed comparison output signal corresponding to a comparison result; and
a holding circuit that outputs an optical signal detection signal representing the presence/absence of input of the optical signal based on the pulsed comparison output signal, and
said amplification circuit comprising:
first and second load resistors that have one-terminal sides connected to a power supply potential and generate the positive-phase signal and the negative-phase signal of the differential output signal, respectively; and
a current addition circuit that adjusts a DC load current flowing to at least one of said first and second load resistors in accordance with an adjusted voltage value from an external adjusted voltage source and adjusts a difference between a DC bias of the positive-phase signal of the differential output signal and a DC bias of the negative-phase signal,
wherein said holding circuit comprises:
an analog holding circuit that comprises a holding capacitor to be changed by the pulsed comparison output signal and a discharging resistor connected in parallel to said holding capacitor and removes charges held in said holding capacitor by said discharging resistor, thereby outputting a holding output signal that changes in accordance with the presence/absence of input of the optical signal; and
an output buffer that shapes the holding output signal into a digital logic signal and outputs the optical signal detection signal.