Macromodel of Precise Signal-Phase Meter

This paper presents a precise macromodel of a signal-phase meter, which allows continuous phase measurement during simulation. It has been developed as a support tool during the design process of a signal-conditioning circuit for incremental position encoders. The development of a signal conditioning circuit requires precise measurements of small signal phases, amplitudes and offsets using the analog/digital circuit simulator. The phase measurement cannot be performed directly with a simulator, therefore an appropriate macro-model is needed for a circuit simulator. The structure of the signal-phase meter is based on the conventional signal-phase measuring method and is intended for the measuring of a cosine-signal phase with a known frequency. It recommends that the time variations of an input signal’s parameters (amplitude, phase, frequency, and offset voltage) are slow and small as possible. Rapid change of a signal’s parameters decreases the simulation result’s accuracy. A macro-model’s precision mainly depends on the chosen parameters for the macro-model and for the simulation. We show that with the proposed meter’s model, the phase angle can be measured with an accuracy of more than ±0,02%. 1. Introduction Position encoders are sensors that convert their linear or rotary displacements into appropriate electrical signals and are widely used in many computer-controlled machines. Position signals can be generated by magnetic, capacitive, or optical means, and represent displacement information in absolute or incremental forms [1, 2]. Ideally, the linear optical incremental position encoders produce two 90° shifted analog signals, which enable us to detect the position of an encoder’s head. However, due to encoder’s and optical grating’s mechanical limitations, these signals have unideal sine/cosine shapes, variable amplitudes, offset voltages, and additional phase shifts. The influences of such various unwanted effects are reduced and corrected by a signal-conditioning circuit, which is usually an encoder’s integral part, realized as an integrated circuit. Thus, the signal-conditioning circuit is an analog/digital circuit, generally developed using an analog/digital circuit simulator. The development of such circuit, always requires very precise signal-phase measurements, which cannot be performed directly by a simulator. This paper deals with the SPICE macromodel of signal-phase meter, which enables a precise phase measurement whilst simulation is running. It is based on well-known practically implemented conventional phase-measurement techniques, as