Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Phase shift by less than period of input
Reexamination Certificate
2000-04-20
2002-01-22
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Phase shift by less than period of input
C327S246000, C327S248000, C327S255000, C327S258000
Reexamination Certificate
active
06340908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase adjusting circuit for precisely adjusting phases of two signals having different phases to a phase difference of 90 degrees. Further, the present invention relates to a scaling signal generation circuit for generating a scaling signal having a waveform of a cyclically repeated monotonous increase using the phase adjusting circuit and a position measuring apparatus using the same.
2. Description of the Related Art
As a method of detecting a position of a mobile unit, there is a method using cyclic signals having a phase difference of 90 degrees generated when the mobile unit is detected.
In this position detecting method, as shown in
FIG. 1
, sensors
2
s
and
2
c
for outputting cyclic signals which change as the mobile unit moves (herein after, referred to as “detection signals”) are arranged at predetermined positions so that the phases of the detection signals become different by 90 degrees. Accordingly, two detection signals Ss and Sc ideally having the same amplitudes and a phase difference of 90 degrees are obtained from the two sensors
2
s
and
2
c.
The two detection signals Ss and Sc having the same amplitudes and a phase difference of 90 degrees respectively become functions of the sin &thgr; and cos &thgr; (&thgr; is a phase angle) when they are sine waves. The ratio of the two detection signals can be expressed in the form of a function of tan &thgr;.
Since tan &thgr; is a function cyclically repeating a monotonous increase along with an increase of the phase angle &thgr;, it can be used as a scaling signal. For example, the phase angle can be detected from 0 to 2&pgr; from the value of tan &thgr; and the signs of sin &thgr; and cos &thgr;. When equally dividing one period &lgr; section on the &thgr;-axis into N number of fine steps, a cyclic function expressed by tan &thgr; monotonously increases in a cycle &pgr; for every fine step having a size of &lgr;
along with movement of a mobile unit, and a scaling signal is obtained for every period &lgr; (2&pgr;) section by referring to the signs of sin &thgr; and cos &thgr;. Specifically, if a scaling signal generator
101
finds a function of tan &thgr; from the ratio of two detection signals and calculates its inverse function tan
−1
&thgr;, a linear phase angle &thgr; taking discrete values equally divided into fine steps is obtained and a scaling value x is calculated from the angle &thgr; and the signs of sin &thgr; and cos &thgr;. By increasing the order every period, it becomes possible to measure a position over a long distance of movement.
When using a position measuring apparatus of such a measurement principle, in a reticle alignment mechanism of a stepper or other application used installed in a semiconductor manufacturing apparatus, the required precision and resolution are high. Further, these requirements have become severer every year.
As one means for realizing high precision measurement of position, generally, as shown in
FIG. 1
, a conventional position measuring apparatus requires, in addition to a scaling signal generator
101
for calculating the tan
−1
&thgr; etc., a phase adjuster
102
for adjusting the phase to give the two detection signals a phase difference of exactly 90 degrees and, further, a level adjuster
103
for adjusting the amplitudes of the two signals.
In reality, however, there to no phase adjuster capable of adjusting the phase by an extremely high precision. Up until now, two sensors have been integrally formed by patterning on a substrate to improve the patterning precision at the time of formation and thereby secure the precision required for the phase difference.
On the other hand, to improve the resolution of position measurement, it is generally sufficient to increase the division number N in one period &lgr; section.
To increase the division number N, it is necessary to increase the number of bits of the A/D converter. However, although an 8-bit or 10-bit A/D converter (IC) is available at a low price, an A/D converter of larger bits becomes expensive. Further, a 16-bit or higher A/D converter cannot be easily obtained at the present, so there is a practical limit to the increase of the number of bits of the A/D converter.
Accordingly, the number of bits of the A/D converter Is increased to a certain extent. A further higher resolution of position measurement is attained by making the period (signal period) &lgr; of the detection signal shorter.
The resolution increases as the signal period &lgr; becomes shorter, for example, when the division number N is 400, the resolution becomes 5 &mgr;m with a 2 mm &lgr;, 1 &mgr;m with a 400 &mgr;m &lgr;, and 0.1 &mgr;m with a 40 &mgr;m &lgr;.
If shortening the signal period &lgr; to increase the resolution, however, the relative positional precision between the sensors
2
s
and
2
c
becomes a problem. Namely, as explained above, the relative positions between the two sensors
2
s
and
2
c
depended on the patterning precision, but when the distance between the sensors
2
s
and
2
c
becomes shorter due to making the signal period &lgr; shorter, the phase deviation due to patterning error increases in the signal period &lgr;.
As a result, the positional precision of sensors required for accurately generating two detection signals having a 90 degree phase difference becomes stricter as the period of the detection signal becomes shorter. For example, in order to suppress the deviation of the phase difference of the sensors
2
s
and
2
c
to within 1 degree from 90 degrees, when the signal period &lgr; it 4 mm, the required positional precision becomes 11 &mgr;m—still easy, while when the signal period &lgr; is 400 &mgr;m, the positional precision becomes 1.1 &mgr;m, when the signal period &lgr; is 40 &mgr;m, and the positional precision becomes 0.11 &mgr;m—which is very exacting. Furthermore, in actuality, since the positional deviation of a pattern must not exceed ½ of the resolution, a still stricter positional precision is required.
As explained above, in the position measuring apparatus of the related art, there is a trade-off between the resolution and the phase precision (positional precision of the sensors). Therefore, there has been the disadvantage that the resolution cannot be improved while maintaining a high phase precision.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a phase adjusting circuit capable of providing a high phase precision regardless of the signal period, a scaling signal generation circuit, and a position measuring apparatus using the same.
According to a first aspect of the present invention, there is provided a phase adjusting circuit for adjusting phases of two input signals having different phases and generating a pair of signals having a phase difference of 90 degrees based on them, comprising an input level adjuster for adjusting at least one amplitude of said two input signals to a predetermined level; an adder for adding said two input signals after adjustment of the amplitude level and outputting a sum signal; and a subtractor for subtracting said two input signals after adjustment in amplitude level and outputting a difference signal having a phase of 90 degrees different from said sum signal.
Preferably, the circuit further comprises an output level adjuster for adjusting at least one of the amplitudes of said sum signal and said difference signal to predetermined level.
Preferably, said output level adjuster includes an amplifying circuit for amplifying a signal level of said sum signal or said difference signal.
According to a second aspect of the present invention, there is provided a phase adjusting circuit for adjusting phases of two input signals having different phases and generating a pair of signals having a phase difference of 90 degrees based on them, comprising an input level adjuster for adjusting the amplitude of at least one of said two input signals to a predetermined level and a subtractor for subtracting one input signal fro
Cunningham Terry D.
Frommer William S.
Frommer & Lawrence & Haug LLP
Simon Darren M.
Sony Corporation
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