Note 3 - Revenue From Contracts With Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 26, 2020	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Revenue	$ 103,042	$ 103,042	$ 103,469	$ 300,947	$ 303,856
Percentage of revenue	100.00%	100.00%	100.00%	100.00%	100.00%
UNITED STATES
Revenue	$ 10,455		$ 9,296	$ 33,634	$ 32,352
Percentage of revenue	10.00%		9.00%	11.00%	11.00%
Other Americas [Member]
Revenue	$ 4,857		$ 2,838	$ 12,772	$ 9,518
Percentage of revenue	5.00%		3.00%	4.00%	3.00%
Americas [Member]
Revenue	$ 15,312		$ 12,134	$ 46,406	$ 41,870
Percentage of revenue	15.00%		12.00%	15.00%	14.00%
CHINA
Revenue	$ 58,122		$ 57,301	$ 154,086	$ 157,648
Percentage of revenue	56.00%		55.00%	51.00%	52.00%
TAIWAN, PROVINCE OF CHINA
Revenue	$ 7,505		$ 6,796	$ 24,957	$ 14,147
Percentage of revenue	7.00%		7.00%	8.00%	5.00%
JAPAN
Revenue	$ 4,346		$ 10,262	$ 18,780	$ 31,534
Percentage of revenue	4.00%		10.00%	6.00%	10.00%
Other Asia [Member]
Revenue	$ 9,766		$ 5,285	$ 25,169	$ 22,171
Percentage of revenue	10.00%		5.00%	9.00%	7.00%
Asia [Member]
Revenue	$ 79,739		$ 79,644	$ 222,992	$ 225,500
Percentage of revenue	77.00%		77.00%	74.00%	74.00%
Europe [Member]
Revenue	$ 7,991		$ 11,691	$ 31,549	$ 36,486
Percentage of revenue	8.00%		11.00%	11.00%	12.00%
Product [Member]
Revenue	$ 96,650		$ 97,477	$ 285,871	$ 287,185
Percentage of revenue	94.00%		94.00%	95.00%	95.00%
Product [Member] | Sales Channel, Through Intermediary [Member]
Revenue		$ 84,409	$ 84,135	$ 245,016	$ 248,234
Percentage of revenue		82.00%	81.00%	81.00%	82.00%
Product [Member] | Sales Channel, Directly to Consumer [Member]
Revenue		$ 12,241	$ 13,342	$ 40,855	$ 38,951
Percentage of revenue		12.00%	13.00%	14.00%	13.00%
License and Service [Member]
Revenue	$ 6,392	$ 6,392	$ 5,992	$ 15,076	$ 16,671
Percentage of revenue	6.00%	6.00%	6.00%	5.00%	5.00%