Optical encoder and interpolation circuit and operating method thereof

Patent metadata

Field	Value
Publication number	US-11073413-B2
Application number	US-201916427872-A
Country	US
Kind code	B2
Filing date	May 31, 2019
Priority date	Nov 26, 2018
Publication date	Jul 27, 2021
Grant date	Jul 27, 2021

Abstract

There is provided an interpolation circuit of an optical encoder including a phase shifter circuit, two multiplexers, two digital circuits and four comparators. The phase shifter circuit receives signals sequentially have a 90 degrees phase shift and outputs multiple phase shifted signals. Each of the two multiplexers receives a half of the multiple phase shifted signals and outputs two pairs of phase shifted signals, each pair having 180 degrees phase difference, respectively to two comparators connected thereto. Each of the two digital circuits controls the corresponding multiplexer to select the two pairs of phase shifted signals from the half of the multiple phase shifted signals.

First claim

What is claimed is:

1. An interpolation circuit of an optical encoder, the interpolation circuit comprising:
a phase shifter circuit configured to receive a first signal, a second signal, a third signal and a fourth signal sequentially having a 90-degrees phase shift, and output 4N phase shifted signals, wherein N is an interpolation factor;
a first multiplexer configured to receive 2N phase shifted signals among the 4N phase shifted signals from the phase shifter circuit;
a second multiplexer configured to receive the rest 2N phase shifted signals among the 4N phase shifted signals from the phase shifter circuit;
a first comparator configured to receive a first pair of phase shifted signals via the first multiplexer to generate a first comparison signal;
a second comparator configured to receive a second pair of phase shifted signals via the first multiplexer to generate a second comparison signal;
a first digital circuit configured to determine whether to change the first pair of phase shifted signals and the second pair of phase shifted signals, among the 2N phase shifted signals, respectively inputted into the first comparator and the second comparator according to the first and second comparison signals;
a third comparator configured to receive a third pair of phase shifted signals via the second multiplexer to generate a third comparison signal;
a fourth comparator configured to receive a fourth pair of phase shifted signals via the second multiplexer to generate a fourth comparison signal; and
a second digital circuit configured to determine whether to change the third pair of phase shifted signals and the fourth pair of phase shifted signals, among the rest 2N phase shifted signals, respectively inputted into the third comparator and the fourth comparator according to the third and fourth comparison signals.

2. The interpolation circuit as claimed in claim 1 , wherein the first signal is a sine signal, the second signal is a cosine signal, the third signal and the first signal are 180 degrees output of phase, and the fourth signal and the second signal are 180 degrees output of phase.

3. The interpolation circuit as claimed in claim 1 , wherein
when the first comparison signal and the second comparison have different voltage levels, the first digital circuit is configured to not change the first pair of phase shifted signals and the second pair of phase shifted signals, among the 2N phase shifted signals, respectively inputted into the first comparator and the second comparator, and
when the first comparison signal and the second comparison have identical voltage levels, the first digital circuit is configured to change the first pair of phase shifted signals and the second pair of phase shifted signals, among the 2N phase shifted signals, respectively inputted into the first comparator and the second comparator.

4. The interpolation circuit as claimed in claim 1 , wherein
when the third comparison signal and the fourth comparison signal have different voltage levels, the second digital circuit is configured to not change the third pair of phase shifted signals and the fourth pair of phase shifted signals, among the rest 2N phase shifted signals, respectively inputted into the third comparator and the fourth comparator, and
when the third comparison signal and the fourth comparison signal have identical voltage levels, the second digital circuit is configured to change the third pair of phase shifted signals and the fourth pair of phase shifted signals, among the rest 2N phase shifted signals, respectively inputted into the third comparator and the fourth comparator.

5. The interpolation circuit as claimed in claim 1 , wherein
the first pair of phase shifted signals are 180 degrees out of phase,
the second pair of phase shifted signals respectively have a 360°×2/4N phase shift from the first pair of phase shifted signals,
the third pair of phase shifted signals respectively have a 360°/4N phase shift from the first pair of phase shifted signals, and
the fourth pair of phase shifted signals respectively have a 360°×3/4N phase shift from the first pair of phase shifted signals.

6. The interpolation circuit as claimed in claim 5 , wherein the first pair of phase shifted signals include sin θ1 and sin(θ1+180°), wherein θ1=4n×360°/4N and n is an integer from 0 to (N/2)−1.

7. The interpolation circuit as claimed in claim 1 , further comprising:
a first clock generator configured to generate a first clock signal to the first digital circuit, and
a second clock generator configured to generate a second clock signal to the second digital circuit.

8. The interpolation circuit as claimed in claim 1 , wherein the first signal, the second signal, the third signal and the fourth signal are ramp signals.

9. An optical encoder, comprising:
multiple photodiodes configured to receive modulated light to generate a first signal, a second signal, a third signal and a fourth signal sequentially having a 90-degrees phase shift; and
an interpolation circuit, comprising:
a phase shifter circuit configured to output 4N phase shifted signals according to the first signal, the second signal, the third signal and the fourth signal, wherein N is an interpolation factor;
a first multiplexer and a second multiplexer connected to the phase shifter circuit, and configured to receive the 4N phase shifted signals;
a first comparator and a second comparator configured to respectively receive a first pair of phase shifted signals and a second pair of phase shifted signals via the first multiplexer; and
a third comparator and a fourth comparator configured to respectively receive a third pair of phase shifted signals and a fourth pair of phase shifted signals via the second multiplexer,

wherein 2N phase shifted signals among the 4N phase shifted signals are selectively coupled to the first comparator and the second comparator by the first multiplexer, and the rest 2N phase shifted signals among the 4N phase shifted signals are selectively coupled to the third comparator and the fourth comparator by the second multiplexer.

10. The optical encoder as claimed in claim 9 , further comprising:
a first digital circuit configured to control switches of the first multiplexer to conduct to select the first pair of phase shifted signals and the second pair of phase shifted signals from the 2N phase shifted signals; and
a second digital circuit configured to control switches of the second multiplexer to conduct to select the third pair of phase shifted signals and the fourth pair of phase shifted signals from the rest 2N phase shifted signals.

11. The optical encoder as claimed in claim 9 , wherein the first signal is a sine signal, the second signal is a cosine signal, the third signal and the first signal are 180 degrees output of phase, and the fourth signal and the second signal are 180 degrees output of phase.

12. The optical encoder as claimed in claim 9 , wherein
the first pair of phase shifted signals are 180 degrees out of phase,
the second pair of phase shifted signals respectively have a 360°×2/4N phase shift from the first pair of phase shifted signals,
the third pair of phase shifted signals respectively have a 360°/4N phase shift from the first pair of phase shifted signals, and
the fourth pair of phase shifted signals respectively have a 360°×3/4N phase shift from the first pair of phase shifted signals.

13. The optical encoder as claimed in claim 12 , wherein the first pair of phase shifted signals include sin θ1 and sin(θ1+180°), wherein θ1=4n×360°/4N and n is an integer from 0 to (N/2)−1.

14. The optical encoder as claim

Assignees

• Pixart Imaging Inc

Inventors

• Thor Swee-Lin
• Chew Gim-Eng

Classifications

• H03K5/24 Primary

  the characteristic being amplitude · CPC title

• G01D5/34715 Primary

  Scale reading or illumination devices · CPC title

• G01D5/34792

  with only digital scales or both digital and incremental scales · CPC title

• H03K2005/00052

  by mixing the outputs of fixed delayed signals with each other or with the input signal · CPC title

• H03K2005/00286

  Phase shifter, i.e. the delay between the output and input pulse is dependent on the frequency, and such that a phase difference is obtained independent of the frequency · CPC title