| 摘要 |
PURPOSE:To enhance high resolution and high speed response performance by converting a carrier wave frequency of a phase modulation signal obtained from the output detected in a scale graduation into a lower frequency, and processing interpolation based on said low carrier wave frequency. CONSTITUTION:An output signal is obtained by detecting the magnetic grids recorded in a magnetic scale 1 by magnetic heads 2 and 3. A frequency converter 20 is provided between a band pass filter 12 for taking out the phase modulating signal from an adder amplifier 11 based on said detected signal and a buffer amplifier 13 provided before an amplitude limiter 14. The circuit 20 is composed of a balanced modulator 21, a low pass filter 22, and a second frequency step down circuit 23. Said step down circuit steps down the frequency n.f0 to 4/5n with respect to the reference signal from a reference oscillator 4 and supplies the modulating signal comprising the frequency of 4/5 f0 to the balanced modulator 21. In this constitution, the interpolation process can be performed under the state the interpolation clock frequency is decreased to 4/5f0. |
