| 摘要 |
PURPOSE:To obtain an analogue signal with a good S/N ratio by a simple circuit, by providing two independent interferometer and processing the difference signal of the interference signals therefrom. CONSTITUTION:Two sets of two-phase signals obtained from the light receiving parts of interference fringe measuring parts 20, 21 are set to the two-phase signals A1, A2 (B1, B2) of interferometers. These signal are passed through amplifiers 22-25 to equally align the amplitudes thereof. Thereafter, the sum and difference of said two-phase signals are made according to predetermined formulae by an adder 26(28) and a subtractor 27(29). Therefore, when the outputs from the adder and the subtractor are inputted to multipliers 30-33, values M1-M4 are obtained. Herein, if an initial phase is negated, two-phase signals D1, D2 of difference signals to be calculated are obtained by a subtractor 34 and an adder 35. Because these signals are under the effect of irregularity due to a zero-cross detector used in wave-form shaping, an analogue difference signal with a good S/N ratio is obtained. |
