Stock-Based Compensation (Tables)

6 Months Ended

Jul. 03, 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				Six months ended
	July 3, 2015		June 27, 2014		July 3, 2015		June 27, 2014
Stock-based compensation in:
Cost of revenue	$	422	$	623	$	950	$	1,139
Research and development expense	1,027		1,269		2,175		2,370
Selling, general and administrative expense	2,435		2,669		4,893		4,859
Total stock-based compensation in operating expense	3,462		3,938		7,068		7,229
Total stock-based compensation	$	3,884	$	4,561	$	8,018	$	8,368

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				Six months ended
	July 3, 2015		June 27, 2014		July 3, 2015		June 27, 2014
Expected term (years)	4.60		4.70		4.70		4.70
Volatility	37	%	39	%	38	%	40	%
Risk-free interest rate	1.5	%	1.7	%	1.5	%	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 six months ended July 3, 2015 and June 27, 2014:



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