In February 2014, we closed an underwritten public offering of $201.3 million aggregate principal amount of our 2014 Notes. We received $195.2 million, net of underwriting discounts, from the issuance of the 2014 Notes and incurred approximately $1.1 million in offering-related expenses. The underwriting discount and offering-related expenses are being amortized to interest expense using the effective-interest rate method. The effective interest rate on the 2014 Notes, reflecting the impact of debt discounts and issuance costs, is approximately 3.0%. The 2014 Notes will mature on February 1, 2034, unless earlier converted, redeemed, or repurchased in accordance with the terms of the 2014 Notes. Holders may require us to repurchase all or a portion of their 2014 Notes on each of February 6, 2021, February 6, 2024, and February 6, 2029, at a repurchase price in cash equal to 100% of the principal amount of the 2014 Notes plus accrued and unpaid interest.

We have retired the majority of the 2014 Notes through the issuance of the 2018 Notes and 2019 Notes, as discussed below. As provided by the indenture governing the 2014 Notes, in February 2021, holders of $0.5 million of the 2014 Notes required us to repurchase their notes at 100% of the principal amount plus accrued and unpaid interest. We recorded a loss of $9 thousand on the extinguishment of those notes, representing the difference between the price paid to extinguish the 2014 Notes and their carrying value, including unamortized debt issuance costs. As of December 31, 2021, there was $0.6 million aggregate principal of the 2014 Notes outstanding.

In March 2018, we entered into separate privately negotiated transactions with certain holders of our 2014 Notes to exchange $150.0 million in aggregate principal amount of the 2014 Notes for 2018 Notes, leaving $51.3 million of aggregate principal amount of 2014 Notes outstanding. The 2018 Notes accrued interest at a rate of 2.75%, payable semi-annually. The 2018 Notes were scheduled to mature on February 1, 2034, unless earlier converted, redeemed, or repurchased in accordance with the terms of the indenture governing the 2018 Notes. In the first quarter of 2019, $150.0 million of the 2018 Notes were converted into 19.5 million shares of our common stock and the notes were retired. We recognized a loss of $9.0 million on the conversion of 2018 Notes, which was included in loss on extinguishment of debt in 2019. This amount represents the difference between the fair value of the bonds converted and the carrying value of the bonds at the time of conversion.

In November 2019, we issued $55.0 million aggregate principal amount of 2019 Notes. Net proceeds of the 2019 Notes issuance were $52.7 million, after deductions for commissions and other debt issuance costs. $51.8 million of the proceeds of the 2019 Notes were used to retire $50.2 million aggregate principal amount of our 2014 Notes. We recognized a loss of $3.0 million on the exchange of the 2014 Notes for the 2019 Notes. The loss on extinguishment of debt was calculated as the difference between the reacquisition price (i.e., the fair value of the principal amount of 2019 Notes) and the net carrying value of the 2014 Notes exchanged.

The 2019 Notes bear interest at 5.25% per annum, payable semiannually on June 1 and December 1 of each year, beginning on June 1, 2020. The 2019 Notes will mature on December 1, 2024, unless earlier repurchased or converted pursuant to their terms. The 2019 Notes will be convertible at the option of the holder at any point prior to the close of business on the second scheduled trading day preceding the maturity date. The initial conversion rate of the Notes is 344.8276 shares of the Company’s common stock per $1,000 principal amount of 2019 Notes (which is equivalent to an initial conversion price of approximately $2.90 per share). The conversion rate is subject to adjustment upon the occurrence of certain specified events.

Those certain specified events include voluntary conversion of the 2019 Notes prior to our exercise of the Issuer’s Conversion Option or in connection with a make-whole fundamental change, entitling the holders, under certain circumstances, to a make-whole premium in the form of an increase in the conversion rate determined by reference to a make-whole table set forth in the indenture governing the 2019 Notes. The conversion rate will not be adjusted for any accrued and unpaid interest.

The 2019 Notes will also be convertible at our option upon certain conditions in accordance with the terms of the indenture governing the 2019 Notes. On or after December 1, 2021 to December 1, 2022, if the price of the Company’s common stock has equaled or exceeded 150% of the Conversion Price then in effect for a specified number of days (Issuer’s Conversion Option), we may, at our option, elect to convert the 2019 Notes in whole but not in part into shares of the Company, determined in accordance with the terms of the indenture. On or after December 1, 2022, if the price of the Company’s common stock has equaled or exceeded 130% of the Conversion Price then in effect for a specified number of days, we may, at our option, elect to convert the 2019 Notes in whole but not in part into shares of the Company, determined in accordance with the terms of the indenture.

Offering-related costs for the 2019 Notes were capitalized as debt issuance costs and are recorded as an offset to the carrying value of the 2019 Notes. The debt issuance costs are amortized over the expected term of the 2019 Notes using the effective interest method through the maturity date of December 1, 2024. The effective rate on the 2019 Notes is 6.2%.


	December 31,
	2021		2020
2.75% 2014 Notes due 2034
Principal amount	$	578	$	1,079
Unamortized debt discount	(8)		(16)
Unamortized debt issuance cost	(2)		(4)
Net carrying value of 2014 Notes	$	568	$	1,059

5.25% 2019 Notes due 2024
Principal amount	$	55,000	$	55,000


Unamortized debt issuance cost	(1,408)		(1,835)
Net carrying value of 2019 Notes	$	53,592	$	53,165
Net carrying value of all Notes	$	54,160	$	54,224

On August 2, 2018, we entered into a revolving credit facility with Silicon Valley Bank (as amended, the Revolving Credit Facility) in an aggregate principal amount of up to the lesser of (i) $15.0 million (Maximum Amount) or (ii) the sum of (a) 85% of our eligible receivables and (b) 50% of our eligible inventory, in each case, subject to certain limitations (Borrowing Base), provided that the amount of eligible inventory that may be counted towards the Borrowing Base shall be subject to a cap as set forth in the Revolving Credit Facility.

On August 2, 2021, we amended our Revolving Credit Facility to extend the maturity date to August 2, 2023 and to provide for a new $10.0 million Term Loan Facility (the Term Loan Facility and, together with the Revolving Credit Facility, the Credit Facility). The stated maturity of the Term Loan Facility is July 1, 2025. However, if the principal amount of our convertible debt exceeds $0.6 million as of June 1, 2024 or if the maturity date of our 2019 Notes has not been extended beyond January 1, 2026 by June 1, 2024, then the maturity of the Term Loan Facility will be June 1, 2024. The Credit Facility is collateralized by substantially all our property, other than intellectual property. The Credit Facility also includes a financial covenant that requires us to maintain a minimum Adjusted Quick Ratio, as defined in the agreement, of at least 1.25 to 1.00.

The interest rate on advances made under the Revolving Credit Facility is the greater of (i) prime rate plus 0.50% or (ii) 5.25%. Interest on any outstanding advances is due and payable monthly and the principal balance is due at maturity though loans can be prepaid at any time without penalty. Fees for Revolving Credit Facility include an annual commitment fee of $112,500 and a quarterly unused line fee based on the Borrowing Base. As of December 31, 2021, the Borrowing Base of the Revolving Credit Facility was $9.4 million, of which we had borrowed $6.8 million, leaving $2.5 million available.

As of December 31, 2021 the Term Loan Facility was fully drawn. The interest rate on the Term Loan Facility is the greater of 4% or a floating per annum rate equal to three quarters of one percentage points (0.75%) above the prime rate. Interest on any outstanding term loan advances is due and payable monthly. In addition to the monthly interest payments, a final payment equal to 6.5% of the original principal amount of each advance is due on the earlier of the maturity date or the date the advance is repaid. Principal balances are required to be repaid in twenty-four equal installments beginning on August 1, 2023. The effective interest rate on the Term Loan Facility, reflecting the impact of debt issuance costs, the end-of-term fee and expected timing of principal repayment was 6.3% as of December 31, 2021.


	December 31,
	2021		2020
Term Loan
Principal amount	$	10,000	$	—
End of term fee accretion	79		—
Unamortized debt issuance cost	(30)		—
Net carrying value of term loan	$	10,049	$	—

Credit Facility
Borrowing Base	$9,368		$	15,000
Carrying value of advances under revolving credit agreement	$	6,838	$	—