Note 3 - Revenue From Contracts With Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 02, 2021	Sep. 26, 2020	Jun. 27, 2020	Mar. 28, 2020	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Revenue	$ 107,173	$ 103,042	$ 100,589	$ 97,316	$ 100,237	$ 103,469	$ 102,296	$ 98,091	$ 408,120	$ 404,093	$ 398,799
Percentage of revenue									100.00%	100.00%	100.00%
UNITED STATES
Revenue									$ 43,945	$ 44,330	$ 38,585
Percentage of revenue									11.00%	11.00%	10.00%
Other Americas [Member]
Revenue									$ 18,192	$ 13,606	$ 16,549
Percentage of revenue									4.00%	3.00%	4.00%
Americas [Member]
Revenue									$ 62,137	$ 57,936	$ 55,134
Percentage of revenue									15.00%	14.00%	14.00%
CHINA
Revenue									$ 213,714	$ 206,107	$ 202,983
Percentage of revenue									52.00%	51.00%	51.00%
TAIWAN, PROVINCE OF CHINA
Revenue									$ 30,972	$ 19,746	$ 16,124
Percentage of revenue									8.00%	5.00%	4.00%
JAPAN
Revenue									$ 25,435	$ 42,658	$ 44,033
Percentage of revenue									6.00%	11.00%	11.00%
Other Asia [Member]
Revenue									$ 35,062	$ 30,254	$ 34,979
Percentage of revenue									9.00%	7.00%	9.00%
Asia [Member]
Revenue									$ 305,183	$ 298,765	$ 298,119
Percentage of revenue									75.00%	74.00%	75.00%
Europe [Member]
Revenue									$ 40,800	$ 47,392	$ 45,546
Percentage of revenue									10.00%	12.00%	11.00%
Product [Member]
Revenue									$ 388,502	$ 382,548	$ 380,468
Percentage of revenue									95.00%	95.00%	95.00%
Product [Member] | Sales Channel, Through Intermediary [Member]
Revenue									$ 339,100	$ 331,941	$ 330,719
Percentage of revenue									83.00%	82.00%	83.00%
Product [Member] | Sales Channel, Directly to Consumer [Member]
Revenue									$ 49,402	$ 50,607	$ 49,749
Percentage of revenue									12.00%	13.00%	12.00%
License and Service [Member]
Revenue									$ 19,618	$ 21,545	$ 18,331
Percentage of revenue									5.00%	5.00%	5.00%