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Stock-Based Compensation | 3 Months Ended
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Apr. 03, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Stock-Based Compensation | STOCK-BASED COMPENSATION Stock-based compensation expense consists primarily of expenses for stock options and RSUs granted to employees and shares issued under the ESPP. The following table summarizes stock-based compensation expense (in thousands):
| Three months ended
| April 3, 2015 |  | March 28, 2014
Stock-based compensation in: |  |  |
Cost of revenue | $ | 528 |  |  | $ | 516 |
Research and development expense | 1,148 |  |  | 1,101 |
Selling, general and administrative expense | 2,458 |  |  | 2,190 |
Total stock-based compensation in operating expense | 3,606 |  |  | 3,291 |
Total stock-based compensation | $ | 4,134 |  |  | $ | 3,807 |
The Company is required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. The Company uses historical data to estimate pre-vesting option forfeitures and records stock-based compensation expense only for those awards that are expected to vest. All stock-based payment awards are amortized on a straight-line basis over the requisite service periods of the awards, which are generally the vesting periods. 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
| April 3, 2015 |  | March 28, 2014
Expected term (years) | 4.70 |  |  | 4.70 |
Volatility | 38 | % |  | 40 | %
Risk-free interest rate | 1.6 | % |  | 1.7 | %
Expected dividends | 0.0 | % |  | 0.0 | %
The expected term represents the weighted-average period that the stock options are expected to remain outstanding. The computation of the expected term was determined based on historical experience of similar awards, giving consideration to the contractual terms of the stock-based awards, vesting schedules and expectations of future employee behavior. The Company uses its historical volatility for a period equivalent to the expected term of the options to estimate the expected volatility. The risk-free interest rate that the Company uses in the Black-Scholes option valuation model is based on U.S. Treasury zero-coupon issues with remaining terms similar to the expected term. The Company has never declared or paid any cash dividends and does not plan to pay cash dividends in the foreseeable future, and, therefore, used an expected dividend yield of zero in the valuation model. The weighted-average fair value per share of options granted was $2.63 and $2.35 for the three months ended April 3, 2015 and March 28, 2014, respectively. The fair value of all stock options vested during the three months ended April 3, 2015 and March 28, 2014 were both $1.3 million. The total realized tax benefit attributable to stock options exercised during the three months ended April 3, 2015 and March 28, 2014, in jurisdictions where this expense is deductible for tax purposes, were $120,000 and $185,000, respectively. Restricted Stock Units The aggregate fair value of all RSUs issued during the three months ended April 3, 2015 and March 28, 2014 were $6.1 million and $5.4 million, respectively. Employee Stock Purchase Plan The value of the stock purchase rights under the ESPP consists of: (1) the 15% discount on the purchase of the stock; (2) 85% of the fair value of the call option; and (3) 15% of the fair value of the put option. 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 three months ended April 3, 2015 and March 28, 2014:
| Purchase Period Ending
| June 30, 2015 |  | June 30, 2014
Expected term (years) | 0.49 |  |  | 0.50 |
Volatility | 35 | % |  | 29 | %
Risk-free interest rate | 0.1 | % |  | 0.1 | %
Expected dividends | 0.0 | % |  | 0.0 | %
Estimated weighted average fair value per share at purchase date | $1.74 |  | $1.71
The expected term represents the period of time from the beginning of the offering period to the purchase date. The Company uses its historical volatility for a period equivalent to the expected term of the options to estimate the expected volatility. The risk-free interest rate that the Company uses in the Black-Scholes option valuation model is based on U.S. Treasury zero-coupon issues with remaining terms similar to the expected term. The Company has never declared or paid any cash dividends and does not plan to pay cash dividends in the foreseeable future, and, therefore, used an expected dividend yield of zero in the valuation model. Unrecognized Stock-Based Compensation As of April 3, 2015, the Company had approximately $20.1 million of unrecognized stock-based compensation expense related to the unvested portion of its stock options and RSUs that is expected to be recognized over a weighted-average period of approximately 2.1 years.

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- Definition The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 50 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6406099&loc=d3e25284-112666 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5444-113901 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 + Details
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