Balance Sheet Components | BALANCE SHEET COMPONENTS Accounts Receivable, Net Accounts receivable consists of the following: December 31, 2019 2018 Accounts receivable, gross $ 10,938 $ 7,003 Allowance for doubtful accounts (23 ) (21 ) Accounts receivable, net $ 10,915 $ 6,982 The following is a summary of the change in our allowance for doubtful accounts: Year Ended December 31, 2019 2018 2017 Balance at beginning of year $ 21 $ 47 $ 32 Additions charged (reductions credited) 2 (26 ) 15 Balance at end of year $ 23 $ 21 $ 47 Inventories Inventories consist of the following: December 31, 2019 2018 Finished goods $ 1,630 $ 1,577 Work-in-process 3,771 1,377 Inventories $ 5,401 $ 2,954 We recorded inventory write-downs of $137 , $121 and $349 for the years ended December 31, 2019, 2018 and 2017, respectively. The inventory write-downs were for lower of cost or market and excess and obsolescence exposure. The inventory write-downs were offset by sales of previously written-down inventory of $35 , $152 and $165 for the years ended December 31, 2019, 2018 and 2017, respectively. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist of current prepaid expenses, deposits, income taxes receivable and other receivables. Property and Equipment, Net Property and equipment consists of the following: December 31, 2019 2018 Equipment, furniture and fixtures $ 8,494 $ 9,536 Tooling 6,552 6,552 Software 6,428 5,444 Leasehold improvements 1,392 1,350 22,866 22,882 Accumulated depreciation and amortization (18,258 ) (16,731 ) Property and equipment, net $ 4,608 $ 6,151 Software amortization was $1,320 , $1,407 and $1,501 for the years ended December 31, 2019, 2018 and 2017, respectively. Depreciation and amortization expense for equipment, furniture, fixtures, tooling and leasehold improvements was $2,300 , $2,148 and $2,076 for the years ended December 31, 2019, 2018 and 2017, respectively. Other Assets, Net Other assets consist primarily of deposits, deferred tax assets and licensed technology. Amortization of licensed technology was $217 for the year ended December 31, 2019 and $0 for each of the years ended December 31, 2018 and 2017. Acquired Intangible Assets, Net In connection with the Acquisition, we recorded certain identifiable intangible assets. See Note 3: “Acquisition” for additional information. Acquired intangible assets resulting from this transaction consist of the following: December 31, 2019 2018 Developed technology $ 5,050 $ 5,050 Customer relationships 1,270 1,270 Backlog and tradename 410 410 6,730 6,730 Less: accumulated amortization (4,026 ) (2,522 ) Acquired intangible assets, net $ 2,704 $ 4,208 Intangible assets are amortized over the following estimated useful lives: developed technology and customer relationships, 3 to 5 years; tradename and backlog, 6 to 18 months. Backlog was fully amortized as of December 31, 2018 and tradename was fully amortized as of December 31, 2019. Amortization expense for intangible assets was $1,504 for the year ended December 31, 2019, with $1,192 included in cost of revenue and $312 included in selling, general and administrative on the consolidated statement of operations. As of December 31, 2019, future estimated amortization expense is as follows: Years ending December 31: 2020 1,497 2021 1,117 2022 90 $ 2,704 Acquired intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. Conditions that would trigger an impairment assessment include, but are not limited to, past, current, or expected cash flow or operating losses associated with the asset. There were no such triggering events requiring an impairment assessment of other intangible assets as of December 31, 2019. Goodwill Goodwill resulted from the Acquisition, whereby we recorded goodwill of $18,407 . See Note 3: "Acquisition" for information concerning the acquisition. See Note 2: "Summary of Significant Accounting Policies" for information on our assessment of goodwill impairment. Accrued Liabilities and Current Portion of Long-Term Liabilities Accrued liabilities and current portion of long-term liabilities consist of the following: December 31, 2019 2018 Accrued payroll and related liabilities $ 3,440 $ 4,428 Operating lease liability, current 1,545 — Accrued commissions and royalties 663 900 Current portion of accrued liabilities for asset financings 483 748 Accrued interest payable 397 403 Deferred revenue 146 96 Accrued costs related to restructuring 66 200 Liability for warranty returns 10 13 Other 1,942 3,468 Accrued liabilities and current portion of long-term liabilities $ 8,692 $ 10,256 The following is a summary of the change in deferred revenue and our liability for warranty returns: Year Ended December 31, 2019 2018 2017 Deferred revenue: Balance at beginning of period $ 96 $ 418 $ — Revenue deferred 511 610 418 Revenue recognized (461 ) (932 ) — Balance at end of period $ 146 $ 96 $ 418 Liability for warranty returns: Balance at beginning of year $ 13 $ 17 $ 28 Provision 5 9 2 Charge-offs (8 ) (13 ) (13 ) Balance at end of year $ 10 $ 13 $ 17 Short-Term Line of Credit On December 21, 2010, we entered into a Loan and Security Agreement with Silicon Valley Bank (the "Bank"), which was amended on December 14, 2012, December 4, 2013, December 18, 2015, December 15, 2016, July 21, 2017, December 21, 2017, December 18, 2018 and December 18, 2019 (as amended, the "Revolving Loan Agreement"). The Revolving Loan Agreement provides a secured working capital-based revolving line of credit (the "Revolving Line") in an aggregate amount of up to the lesser of (i) $10,000 , or (ii) $2,500 plus 80% of eligible domestic accounts receivable and certain foreign accounts receivable. The Revolving Line has a maturity date of December 27, 2020. In addition, the Revolving Loan Agreement provides for non-formula advances of up to $10,000 which may be made solely during the last five business days of any fiscal month or quarter and which must be repaid by the Company on or before the fifth business day after the applicable fiscal month or quarter end. Amounts advanced under the Revolving Line bear interest at an annual rate equal to the lender's prime rate plus 0.25% . The Revolving Loan Agreement, as amended also provides an option for LIBOR advances that bear interest based on the LIBOR rate, subject to the availability of a LIBOR rate. Interest on the Revolving Line is due monthly, with the balance due on December 27, 2020, which is the scheduled maturity date for the Revolving Line. The Revolving Loan Agreement, as amended contains customary affirmative and negative covenants, including with respect to the following: compliance with laws, provision of financial statements and periodic reports, payment of taxes, maintenance of inventory and insurance, maintenance of operating accounts at the Bank, the Bank's access to collateral, formation or acquisition of subsidiaries, incurrence of indebtedness, dispositions of assets, granting liens, changes in business, ownership or business locations, engaging in mergers and acquisitions, making investments or distributions and affiliate transactions. The covenants also require that the Company maintain a minimum ratio of qualifying financial assets to the sum of qualifying financial obligations. The Revolving Loan Agreement, as amended also contains customary events of default, including the following: defaults with respect to covenant compliance, the occurrence of a material adverse change, the occurrence of certain bankruptcy or insolvency events, cross-defaults, judgment defaults and material misrepresentations. The occurrence of an event of default could result in the acceleration of the Company's obligations under the Revolving Loan Agreement, as amended and an increase to the applicable interest rate, and would permit the Bank to exercise remedies with respect to its security interest. To secure the repayment of any amounts borrowed under the Revolving Loan Agreement, as amended, the Company granted to the Bank a security interest in substantially all of its assets, excluding its intellectual property assets. The Company has agreed not to pledge or otherwise encumber its intellectual property assets without prior written permission from the Bank. As of December 31, 2019 and December 31, 2018, we had no |