Note 3 - Revenue From Contracts With Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Revenue	$ 97,316	$ 98,091
Percentage of revenue	100.00%	100.00%
UNITED STATES
Revenue	$ 13,319	$ 12,895
Percentage of revenue	14.00%	13.00%
Other Americas [Member]
Revenue	$ 3,268	$ 3,975
Percentage of revenue	3.00%	4.00%
Americas [Member]
Revenue	$ 16,587	$ 16,870
Percentage of revenue	17.00%	17.00%
CHINA
Revenue	$ 43,499	$ 48,305
Percentage of revenue	45.00%	49.00%
TAIWAN, PROVINCE OF CHINA
Revenue	$ 9,859	$ 2,678
Percentage of revenue	10.00%	3.00%
JAPAN
Revenue	$ 7,999	$ 11,857
Percentage of revenue	8.00%	12.00%
Other Asia [Member]
Revenue	$ 7,336	$ 6,171
Percentage of revenue	8.00%	7.00%
Asia [Member]
Revenue	$ 68,693	$ 69,011
Percentage of revenue	71.00%	71.00%
Europe [Member]
Revenue	$ 12,036	$ 12,210
Percentage of revenue	12.00%	12.00%
Product [Member]
Revenue	$ 93,225	$ 91,612
Percentage of revenue	96.00%	93.00%
Product [Member] | Sales Channel, Through Intermediary [Member]
Revenue	$ 75,455	$ 77,472
Percentage of revenue	78.00%	79.00%
Product [Member] | Sales Channel, Directly to Consumer [Member]
Revenue	$ 17,770	$ 14,140
Percentage of revenue	18.00%	14.00%
License and Service [Member]
Revenue	$ 4,091	$ 6,479
Percentage of revenue	4.00%	7.00%