| 摘要 |
In a digital phase ramp type fiber optic gyro in which a digital biasing signal produced by a biasing signal generator is added to a digital ramp signal and the added output is converted by a D/A converter to an analog signal and is applied to an optical phase modulator to thereby cancel a Sagnac phase difference of right-handed light and left-handed light propagating through a looped optical transmission line and provide +.pi./2 rad. and -.pi./2 rad. bias phase differences alternately with each other, a first error signal corresponding to the difference between the outputs of an opto-electric converter when the +.pi./2 rad. and -.pi./2 rad. phase differences are provided, respectively, is detected from the output of the opto-electric converter for converting interference light of the right-handed and the left-handed light into an electric signal, and the step value of the digital ramp signal is determined, based on the first error signal. An accumulator accumulates the step value and, when the accumulated output exceeds 2m.pi. (where m is a positive integer), causes an overflow and a sign signal indicating the sign of the overflow. The digital ramp signal, which is the accumulated output, is converted by a D/A converter to an analog signal, which is provided to the optical phase modulator. A second error signal detector detects, as a second error signal, the difference between the outputs of the opto-electric converter at an operating point when the overflow occurs and at the immediately preceding operating point. Based on the overflow sign signal and a sign signal indicating the sign of the biasing signal at the time of occurrence of the overflow, a negative feedback control circuit determines which of +(4m-1)x.pi./2, -(4m-1)x.pi./2, -(4m+1)x.pi./2 and +(4m+1)x.pi./2 the operating at the time of occurrence of the overflow corresponds to, and multiplies the second error signal by a positive or negative sign dependent on the result of determination to create a negative feedback error signal, thereby controlling the conversion gain of the D/A converter. |
