Phase shifter circuit of optical encoder and operating method thereof
AssigneePixart Imaging Inc.
InventorsChung-Min Thor, Kuan-Choong Shim, Gim-Eng Chew
Life of this patent
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Abstract
There is provided a phase shifter circuit of an optical encoder that receives four signals generated from photodiodes. The phase shifter circuit includes four resistor strings each coupled to two of the four signals having a 90-degrees phase pitch. By taping out different numbers of signals at different tape-out nodes of each of the four resistor strings, the phase shifter circuit is adapted to output signals for different interpolation factors without changing the mask set.
Claims20
A phase shifter circuit of an optical encoder, the phase shifter circuit being configured to receive a first signal, a second signal, a third signal and a fourth signal sequentially having a 90-degrees phase shift, the phase shifter circuit comprising:
- a first resistor string having M identical first resistors cascaded together, and two ends of the first resistor string configured to receive the first signal and the second signal, respectively;
- a second resistor string having M identical second resistors cascaded together, and two ends of the second resistor string configured to receive the second signal and the third signal, respectively;
- a third resistor string having M identical third resistors cascaded together, and two ends of the third resistor string configured to receive the third signal and the fourth signal, respectively;
- a fourth resistor string having M identical fourth resistors cascaded together, and two ends of the fourth resistor string configured to receive the fourth signal and the first signal, respectively;
- and
- 4×(M−1) tape-out nodes respectively located between every two adjacent resistors of the M first resistors, the M second resistors, the M third resistors and the M fourth resistors,
- wherein a number of tape-out signals from each of the first, second, third and fourth resistor strings is equal to an interpolation factor N of the optical encoder subtracted by 1.
An optical encoder, comprising:
- photodiodes, configured to receive light from a code medium to output a first signal, a second signal, a third signal and a fourth signal sequentially having a 90-degrees phase shift;
- a phase shifter circuit, comprising 4 resistor strings each having M identical resistors cascaded together and respectively receiving two of the first, second, third and fourth signals having the 90-degrees phase shift, wherein a number of tape-out signals from each of the 4 resistor strings is equal to an interpolation factor N of the optical encoder subtracted by 1;
- and
- a comparison logic circuit coupled to the phase shifter circuit, and configured to use the first, second, third and fourth signals as well as the 4×(N−1) tape-out signals from the 4 resistor strings to generate two N-fold interpolation signals.
An operating method of a phase shifter circuit of an optical encoder, the phase shifter circuit comprising 4 resistor strings each comprising M identical resistors cascaded together and (M−1) tape-out nodes respectively located between every two adjacent resistors of the M identical resistors, and each resistor string receiving two signals among four signals having a 90-degrees phase pitch, the operating method comprising:
- taping out a first number of tape-out signals at first tape-out nodes from each of the 4 resistor strings when the optical encoder is set as a first interpolation factor N1;
- and
- taping out a second number of tape-out signals at second tape-out nodes from each of the 4 resistor strings when the optical encoder is set as a second interpolation factor N2 different from the first interpolation factor N1,
- wherein the first tape-out nodes are determined according to values of 360°/4N1 and multiples of 360°/4N1, and the second tape-out nodes are determined according to values of 360°/4N2 and multiples of 360°/4N2.
Dependencies are inferred from the claim text.