Note 3 - Revenue From Contracts With Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Revenue	$ 100,589	$ 102,296	$ 197,905	$ 200,387
Percentage of revenue	100.00%	100.00%	100.00%	100.00%
UNITED STATES
Revenue	$ 9,860	$ 10,161	$ 23,179	$ 23,056
Percentage of revenue	10.00%	10.00%	12.00%	12.00%
Other Americas [Member]
Revenue	$ 4,647	$ 2,705	$ 7,915	$ 6,680
Percentage of revenue	4.00%	2.00%	4.00%	3.00%
Americas [Member]
Revenue	$ 14,507	$ 12,866	$ 31,094	$ 29,736
Percentage of revenue	14.00%	12.00%	16.00%	15.00%
CHINA
Revenue	$ 52,465	$ 52,042	$ 95,964	$ 100,347
Percentage of revenue	52.00%	51.00%	48.00%	50.00%
TAIWAN, PROVINCE OF CHINA
Revenue	$ 7,593	$ 4,672	$ 17,452	$ 7,351
Percentage of revenue	8.00%	5.00%	9.00%	4.00%
JAPAN
Revenue	$ 6,435	$ 9,415	$ 14,434	$ 21,272
Percentage of revenue	6.00%	9.00%	7.00%	11.00%
Other Asia [Member]
Revenue	$ 8,067	$ 10,716	$ 15,403	$ 16,886
Percentage of revenue	8.00%	11.00%	8.00%	8.00%
Asia [Member]
Revenue	$ 74,560	$ 76,845	$ 143,253	$ 145,856
Percentage of revenue	74.00%	76.00%	72.00%	73.00%
Europe [Member]
Revenue	$ 11,522	$ 12,585	$ 23,558	$ 24,795
Percentage of revenue	12.00%	12.00%	12.00%	12.00%
Product [Member]
Revenue	$ 95,996	$ 98,096	$ 189,221	$ 189,708
Percentage of revenue	96.00%	96.00%	96.00%	95.00%
Product [Member] | Sales Channel, Through Intermediary [Member]
Revenue	$ 85,152	$ 86,627	$ 160,607	$ 164,099
Percentage of revenue	85.00%	85.00%	81.00%	82.00%
Product [Member] | Sales Channel, Directly to Consumer [Member]
Revenue	$ 10,844	$ 11,469	$ 28,614	$ 25,609
Percentage of revenue	11.00%	11.00%	15.00%	13.00%
License and Service [Member]
Revenue	$ 4,593	$ 4,200	$ 8,684	$ 10,679
Percentage of revenue	4.00%	4.00%	4.00%	5.00%