Intangible Assets

In connection with our acquisitions of Silicon Image, Inc. in March 2015 and SiliconBlue Technologies, Inc. in December 2011, we recorded identifiable intangible assets related to developed technology, customer relationships, licensed technology, patents, and in-process research and development based on guidance for determining fair value under the provisions of ASC 820, "Fair Value Measurements." Additionally, during the fiscal years presented, we licensed additional third-party technology. We do not believe there is any significant residual value associated with these intangible assets. We are amortizing the intangible assets using the straight-line method over their estimated useful lives.

The following tables summarize the details of our Intangible assets, net as of December 28, 2019 and December 29, 2018:



	December 28, 2019
(In thousands)	Weighted Average Amortization Period (in years)	Gross		Accumulated Amortization			Intangible assets, net
Developed technology	5.0	$	110,987	$	(105,594	)	$	5,393
Customer relationships	5.8	22,934		(21,400		)	1,534
Licensed technology	5.0	459		(409		)	50
Total identified intangible assets		$	134,380	$	(127,403	)	$	6,977



	December 29, 2018
(In thousands)	Weighted Average Amortization Period (in years)	Gross		Accumulated Amortization			Intangible assets, net
Developed technology	5.0	$	110,987	$	(94,389	)	$	16,598
Customer relationships	5.8	22,934		(19,048		)	3,886
Licensed technology	5.0	1,194		(353		)	841
Total identified intangible assets		$	135,115	$	(113,790	)	$	21,325

We recorded amortization expense related to intangible assets on the Consolidated Statements of Operations as presented in the following table:



	Year Ended
(In thousands)	December 28, 2019		December 29, 2018		December 30, 2017
Research and development	$	55	$	277	$	569
Amortization of acquired intangible assets	13,558		17,690		31,340
	$	13,613	$	17,967	$	31,909

The annual expected amortization expense of acquired intangible assets is as follows:



(In thousands)	Amount
2020	$	4,500
2021	2,239
2022	238
Total	$	6,977

No impairment charges relating to acquired intangible assets were recorded for fiscal 2019 as no indicators of impairment were present. During the third quarter of fiscal 2018, we concluded that a certain product line had limited future revenue potential due to a decline in customer demand for that product, and we recorded an impairment charge of $0.6 million to the intangible asset associated with that product. During the second quarter of 2018, we recorded an impairment charge relating to intangible assets of $11.9 million as a result of the strategic decision to discontinue our millimeter wave business. During fiscal 2017, we recorded a net impairment charge of $32.4 million related to certain of the developed technology intangible assets acquired in our acquisition of Silicon Image. These charges were recorded to Impairment of acquired intangible assets in the Consolidated Statements of Operations.