US 11,852,472 B2
Output signal processing circuit for eddy current sensor and output signal processing method for eddy current sensor
Hiroto Yamada, Tokyo (JP); Taro Takahashi, Tokyo (JP); Hiroaki Shibue, Tokyo (JP); Atsushi Abe, Tokyo (JP); and Shinpei Tokunaga, Tokyo (JP)
Assigned to EBARA CORPORATION, Tokyo (JP)
Filed by EBARA CORPORATION, Tokyo (JP)
Filed on Dec. 15, 2020, as Appl. No. 17/122,301.
Claims priority of application No. 2019-226547 (JP), filed on Dec. 16, 2019; and application No. 2019-226549 (JP), filed on Dec. 16, 2019.
Prior Publication US 2021/0199415 A1, Jul. 1, 2021
Int. Cl. G01B 7/06 (2006.01); H01L 21/67 (2006.01)
CPC G01B 7/105 (2013.01) [H01L 21/67253 (2013.01)] 6 Claims
OG exemplary drawing
 
1. An eddy current sensor output signal processing circuit, that processes first and second output signals output by an eddy current sensor including first and second coils that respectively output the first and second output signals, the output signal processing circuit comprising:
a first mixer circuit that accepts the first output signal and a signal of a predetermined frequency as input, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a first low-pass filter that accepts the output signal output by the first mixer circuit as input, cuts a high-frequency signal included in the output signal received as input, and outputs at least a DC signal;
a second mixer circuit that accepts the second output signal and the signal of the predetermined frequency as input, multiplies the two input signals, and outputs an output signal obtained by the multiplication;
a second low-pass filter that accepts the output signal output by the second mixer circuit as input, cuts a high-frequency signal included in the output signal received as input, and outputs at least a DC signal; and
a first subtractor circuit that accepts the DC signal output by the first low-pass filter and the DC signal output by the second low-pass filter as input, obtains a difference between the two input DC signals, and outputs the obtained difference,
wherein
the eddy current sensor includes third and fourth coils that respectively output third and fourth output signals, and
the output signal processing circuit includes
a third mixer circuit that accepts the third output signal and the signal of the predetermined frequency as input, multiplies the two input signals, and outputs an output signal obtained by the multiplication,
a third low-pass filter that accepts the output signal output by the third mixer circuit as input, cuts a high-frequency signal included in the output signal received as input, and outputs at least a DC signal,
a fourth mixer circuit that accepts the fourth output signal and the signal of the predetermined frequency as input, multiplies the two input signals, and outputs an output signal obtained by the multiplication,
a fourth low-pass filter that accepts the output signal output by the fourth mixer circuit as input, cuts a high-frequency signal included in the output signal received as input, and outputs at least a DC signal,
a second subtractor circuit that accepts the DC signal output by the third low-pass filter and the DC signal output by the fourth low-pass filter as input, obtains a difference between the two input DC signals, and outputs the obtained difference, and
an adder circuit that accepts the difference output by the first subtractor circuit and the difference output by the second subtractor circuit as input, obtains a sum of the two input differences or a difference between the two input differences, and outputs the obtained sum or difference.