JPS5837483B2 - phase detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a phase detection circuit suitable for a length measurement system that detects displacement as a change in the phase of an electrical signal.

FIG. 1 shows a conventional phase detection circuit.

Referring to the figure, the oscillator 1 has a carrier frequency f.

A reference signal having a frequency n times that of the reference signal is generated, and the reference signal is applied to the downshifter 2 and the dividing circuit 15.

The downshifter 2 makes the frequency of the reference signal 1 the same, and supplies it to the magnetic head 8 of channel 1 through the phase shifter 3 and amplifier 4 to the magnetic head 7 of channel 2. has amplifier 5
It is excited by supplying it through.

A balanced modulation signal obtained by the relative displacement between the magnetic scale 6 and both heads 7 and 8 is added by an adder 11 via preamplifiers 9 and 10, and converted into a phase modulation signal having a phase change corresponding to the displacement. After that, bandpass filter 1
2. The signal is applied to the dividing circuit 15 via the amplifier 13 and the waveform shaping circuit 14.

The dividing circuit 15 is a so-called interpolation circuit as described, for example, in Japanese Patent Publication No. 5028032, and generates a positive direction movement pulse P0 and a negative direction movement pulse P- whose directions are discriminated according to the amount of displacement. .

However, according to the conventional method described above, when trying to obtain high resolution accuracy, one wavelength of the phase modulation signal corresponds to the scale recording wavelength (pitch), so it is necessary to divide (
(interpolation) must increase the frequency of the clock pulses.

There are restrictions such as lowering the frequency of the residual phase modulation signal, such as lowering the response speed.

Therefore, in the conventional method, it is usually 10KH depending on the resolution.
z and 50 KHz phase modulation signals are used.

Therefore, as the bandpass filter 12 for removing unnecessary components of the output signals of the magnetic heads 7 and 8, filters corresponding to the frequencies of the phase modulation signal [OKHz] and 50KHz are required, so it is necessary to use coils and capacitors. A passive filter must be used, which is large and expensive, and is extremely disadvantageous in terms of cost and space.

In view of these circumstances, the present invention aims to solve the above-mentioned drawbacks of the prior art by increasing the manual frequency of the bandpass filter, and will be described below with reference to embodiments shown in the drawings.

The embodiment of the present invention shown in FIG. 2 differs from FIG. A comparator 18 is inserted respectively, and the frequency nf from the oscillator 1 is
The reason is that it is configured to be excited by the reference signal of c.

However, X represents the amount of displacement, and λ represents the pitch of the scale.

Next, as the bandpass filter 7, for example, the lower sideband (n]) fc or the upper sideband (
n + 1) fc as the passband and pass the 2π balanced modulation wave signal e2, the phase change amount -Xλ is preserved and only the carrier frequency is (n-1') or (
A phase modulated signal multiplied by n+1) is obtained.

This signal is further applied to a phase comparator 18 via an amplifier 13 and a waveform shaping circuit 14.

The phase comparator 18 is composed of, for example, a D flip-flop, and has a carrier frequency fo when adding the signal e2.
Convert to a square wave with a frequency equal to .

This rectangular wave signal is completely equivalent to the output signal of the waveform shaping circuit 14 shown in FIG. 1, and the dividing circuit 15 obtains a pulse corresponding to the amount of displacement.

? According to the present invention, the pass frequency band of the bandpass filter can be increased, so that a small and inexpensive cellac filter or the like can be used in place of the conventional passive filter.

As a result, even if a balanced modulator and a phase comparator are added, inexpensive IC circuits can be used for these, which is extremely advantageous in terms of cost and space.

In the above embodiment, the phase of the excitation signal of the head is shifted by -, but the phase of the carrier of the balanced modulation wave signal of the four channels is shifted by π by excitation with the in-phase signal.
A similar phase modulation signal can be obtained by adding the signals of both channels after shifting by /2.

The present invention can be widely applied not only to a length measurement system using a magnetic scale and a magnetic head, but also to a system that detects displacement as a phase change of an electric signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional phase detection circuit.
FIG. 2 is a block diagram showing one embodiment of the present invention. 1: clock oscillator, 6: magnetic scale, 7, 8: magnetic head, 15: dividing circuit, 16: balanced modulator, 17 bandpass filter, 18: phase comparator.

Claims (1)

[Claims] 1. A circuit that generates a phase modulation signal with a frequency fc having a phase corresponding to the amount of displacement, a phase modulation signal from the circuit, and a frequency nfc corresponding to the number of divisions n with respect to the scale recording wavelength λ. A balanced modulator to which a clock signal is applied and a frequency (n-1)f or (n +
I) A phase detection circuit comprising: a bandpass filter that passes a balanced modulation signal C of fc; and a phase comparator to which the signal passed through the filter and the clock signal are applied.