Stock-Based Compensation (Tables)

9 Months Ended

Oct. 02, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense (in thousands):



	Three months ended				Nine months ended
	October 2, 2015		September 26, 2014		October 2, 2015		September 26, 2014
Stock-based compensation in:
Cost of revenue	$	433	$	612	$	1,383	$	1,751
Research and development expense	1,074		1,219		3,249		3,589
Selling, general and administrative expense	2,320		2,521		7,213		7,380
Total stock-based compensation in operating expense	3,394		3,740		10,462		10,969
Total stock-based compensation	$	3,827	$	4,352	$	11,845	$	12,720

Valuation Assumptions for Stock Options

The Company estimated the fair value of all employee stock options using a Black-Scholes valuation model with the following weighted average assumptions:



	Three months ended				Nine months ended
	October 2, 2015		September 26, 2014		October 2, 2015		September 26, 2014
Expected term (years)	4.60		4.70		4.70		4.70
Volatility	37	%	40	%	38	%	40	%
Risk-free interest rate	1.5	%	1.8	%	1.6	%	1.7	%
Expected dividends	0.0	%	0.0	%	0.0	%	0.0	%

Employee Stock Purchase Plan

The call option and put option were valued using the Black-Scholes option pricing model. The weighted average fair value of the Company’s ESPP shares at purchase dates was estimated using the following weighted average assumptions during the nine months ended October 2, 2015 and September 26, 2014:



	Purchase Period Ending
	December 31, 2015		June 30, 2015		December 31, 2014		June 30, 2014
Expected term (years)	0.50		0.50		0.50		0.50
Volatility	32	%	35	%	33	%	28	%
Risk-free interest rate	0.1	%	0.1	%	0.1	%	0.1	%
Expected dividends	0.0	%	0.0	%	0.0	%	0.0	%
Estimated weighted average fair value per share at purchase date	$1.64		$1.75		$1.84		$1.70