Stock-Based Compensation (Tables)

6 Months Ended

Jun. 27, 2014

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
	June 27, 2014		June 28, 2013		June 27, 2014		June 28, 2013
Stock-based compensation in:
Cost of revenue	$	623	$	622	$	1,139	$	1,233
Research and development expense	1,269		1,121		2,370		2,324
Selling, general and administrative expense	2,669		2,279		4,859		4,364
Total stock-based compensation in operating expense	3,938		3,400		7,229		6,688
Total stock-based compensation	$	4,561	$	4,022	$	8,368	$	7,921

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
	June 27, 2014		June 28, 2013		June 27, 2014		June 28, 2013
Expected term (years)	4.70		4.70		4.70		4.70
Volatility	39	%	49	%	40	%	51	%
Risk-free interest rate	1.7	%	1.1	%	1.7	%	0.8	%
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 June 27, 2014 and June 28, 2013:



	Purchase Period Ending
	June 30, 2014		June 30, 2013
Expected term (years)	0.50		0.49
Volatility	28	%	30	%
Risk-free interest rate	0.1	%	0.2	%
Expected dividends	0.0	%	0.0	%
Estimated weighted average fair value per share at purchase date	$1.70		$1.23