1. A receiving circuit comprising:
a light receiving element receiving a light signal and outputting a light current corresponding to the light signal;
a signal voltage generation portion converting the light current into a signal voltage and outputting the signal voltage;
a comparator comparing the signal voltage with a first threshold value or a second threshold value;
a reference voltage generation portion outputting a reference voltage input to the comparator; and
a switch changing the reference voltage to one of the first threshold value and the second threshold value based on an output of the comparator.
2. The circuit according to claim 1, wherein the reference voltage generation portion includes a reference diode equivalent to the light receiving element.
3. The circuit according to claim 2, wherein
the light receiving element is a photodiode, and
the reference diode is provided on the same substrate as the photodiode and has a shielded light receiving surface.
4. The circuit according to claim 1, wherein
the reference voltage generation portion includes a transimpedance amplifier, and
the switch changes a value of a feedback resistor of the transimpedance amplifier.
5. The circuit according to claim 1, further comprising:
a resistor provided between an output terminal of the reference voltage generation portion and an input terminal of the comparator,
wherein the switch changes a value of the resistor.
6. The circuit according to claim 1, wherein the reference voltage includes an offset voltage.
7. The circuit according to claim 6, wherein the switch varies the offset current and switches the reference voltage.
8. The circuit according to claim 7, wherein the switch includes a current mirror circuit.
9. The circuit according to claim 7, wherein
the reference voltage generation portion includes a transimpedance amplifier, and
the switch changes an offset current flowing through a feedback resistor of the transimpedance amplifier.
10. The circuit according to claim 9, wherein the transimpedance amplifier includes a plurality of feedback resistors connected in series, and the offset current is supplied between the plurality of feedback resistors.
11. The circuit according to claim 1, wherein the signal voltage generation portion and the reference voltage generation portion include a common transimpedance amplifier that operates in a differential mode.
12. The circuit according to claim 11, wherein a differential amplifier is provided between the transimpedance amplifier and the comparator.
13. The circuit according to claim 1, wherein the reference voltage generation portion includes a first transimpedance amplifier, and the signal voltage generation portion includes a second transimpedance amplifier.
14. The circuit according to claim 1, wherein the switch further includes a noise canceling circuit which generates noise equivalent to switching noise, and an output of the noise canceling circuit is input to the signal voltage generation portion.
15. The circuit according to claim 14, wherein the noise canceling circuit is onoff-controlled in synchronization with the switch circuit.
16. The circuit according to claim 1, further comprising:
an output stage including a CMOS converter operating in accordance with an output of the comparator; and
a DTC circuit provided between the output stage and the comparator.
17. The circuit according to claim 1, further comprising a switch circuit controlling the switch in accordance with an output of the comparator.
18. The circuit according to claim 17, wherein the switch circuit includes a DFF (Delayed Flip Flop).
19. The circuit according to claim 1, wherein the switch includes a CMOS switch and operates in analog mode.
20. The circuit according to claim 19, wherein the switch includes a low-pass filter.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A power steering apparatus equipped in a vehicle provided with a rack and pinion type steering mechanism converting a rotation of a pinion shaft in response to an operation of a steering member into a displacement in an axial direction of a rack shaft to execute steering, comprising:
a torque detector;
a steering actuator operating based on a torque detected by said torque detector and applying a steering assisting force to said rack shaft; and
an intermediate gear engaging with a pinion provided in said pinion shaft and rack teeth provided in said rack shaft, and transmitting the rotation of said pinion shaft to said rack shaft,
wherein said torque detector includes:
a first force sensor detecting a force applied to said pinion shaft;
a second force sensor detecting a force applied to a support shaft of said intermediate gear; and
a torque calculating unit calculating said torque detected by said torque detector detecting a steering torque applied by said steering member, based on a difference of the forces detected by said first force sensor and the second force sensor.
2. A power steering apparatus according to claim 1, further comprising an assist control unit accepting said torque as an input, and outputting a control signal to said steering actuator for allowing said steering actuator to generate said steering assisting force based on the accepted torque,
wherein said calculating unit calculates said torque in accordance with a value obtained by subtracting the force detected by said second force sensor from the force detected by said first force sensor, and outputs the calculated torque to said assist control unit, and
wherein said assist control unit determines whether or not the accepted torque is positive, and
wherein, when a determination result is affirmative, said assist control unit outputs said control signal corresponding to said steering assisting force based on said torque, to said steering actuator, so as to apply a positive feedback to the operation of said steering member.
3. A power steering apparatus according to claim 2,
wherein, when said determination result is negative, said assist control unit further determines whether or not an absolute value of said torque is larger than a predetermined value, and,
wherein, when a further determination result is affirmative, said assist control unit calculates a canceling force to at least partly cancel the operation of said steering member based on said torque, and outputs said control signal corresponding to the calculated canceling force as a negative steering assisting force, to said steering actuator.
4. A power steering apparatus as claimed in claim 2, wherein the forces of said first and second force sensors are filter processed by a high pass filter.