Stock-Based Compensation (Tables)

9 Months Ended

Sep. 27, 2013

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
	September 27, 2013		September 28, 2012		September 27, 2013		September 28, 2012
Stock-based compensation in:
Cost of revenue	$	605	$	659	$	1,838	$	2,176
Research and development expense	1,076		1,450		3,400		4,755
Selling, general and administrative expense	2,264		2,388		6,628		6,816
Total stock-based compensation in operating expense	3,340		3,838		10,028		11,571
Total stock-based compensation	$	3,945	$	4,497	$	11,866	$	13,747

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
	September 27, 2013		September 28, 2012		September 27, 2013		September 28, 2012
Expected term (years)	4.70		4.70		4.70		4.70
Volatility	46	%	54	%	51	%	56	%
Risk-free interest rate	1.5	%	0.7	%	0.8	%	0.9	%
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 with the following assumptions:

	Purchase Period Ending		Purchase Period Ending
	June 30, 2013		June 30, 2012		December 31, 2012
Expected term (years)	0.49		0.50		0.50
Volatility	30	%	53	%	46	%
Risk-free interest rate	0.2	%	0.2	%	0.2	%
Expected dividends	0.0	%	0.0	%	0.0	%