CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 28, 2019	Dec. 28, 2019
Cash flows from operating activities:
Net loss		$ (22,437)	$ (24,370)	$ (33,500)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense		1,147	866
Stock-based compensation expense		1,716	572
Change in fair value of preferred stock warrant liability	$ 0		341
Non-cash interest expense and end of term accretion expense		379	352
Net amortization (accretion) of premiums (discounts) on marketable securities		304	(136)
Unrealized foreign currency transaction (gains) losses		(523)	392
Changes in operating assets and liabilities:
Accounts receivable		472	(3,098)
Inventory		(2,397)	(3,238)
Prepaid expenses and other current assets		(736)	(314)
Accounts payable		(6,417)	1,054
Accrued expenses and other current liabilities		3,320	2,954
Deferred revenue		1,156	(136)
Deferred rent		889	(261)
Net cash used in operating activities		(23,127)	(25,022)
Cash flows from investing activities:
Purchases of property and equipment		(453)	(184)
Purchases of marketable securities		(101,512)	(67,677)
Proceeds from sales and maturities of marketable securities		50,483
Net cash used in investing activities		(51,482)	(67,861)
Cash flows from financing activities:
Payments of public offering costs and other financing costs		(705)	(4,506)
Proceeds from issuance of common stock in public offering, net of underwriting discounts and commissions		75,670	97,367
Proceeds from issuance of common stock upon exercise of stock options		194	108
Proceeds from issuance of common stock in connection with employee stock purchase plan		357
Proceeds from Paycheck Protection Program loan		2,249
Repayment of Paycheck Protection Program loan		(2,249)
Net cash provided by financing activities		75,516	92,969
Effect of exchange rate changes on cash, cash equivalents and restricted cash		398	80
Net increase in cash, cash equivalents and restricted cash		1,305	166
Cash, cash equivalents and restricted cash, beginning of period		20,592	20,741	20,741
Cash, cash equivalents and restricted cash, end of period	21,897	21,897	20,907	20,592
Supplemental disclosure of non-cash investing and financing activities:
Conversion of convertible preferred stock to common stock upon initial public offering			186,519
Settlement of accrued financing fee			124
Transfers of inventory to property and equipment		705	1,904
Reclassification of warrants to additional paid-in capital			1,239
Purchases of property and equipment included in accounts payable		26	90
Offering costs included in accounts payable and accrued expenses			120
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	21,397	21,397	20,407	20,092
Restricted cash	500	500	500
Cash, cash equivalents and restricted cash, end of period	$ 21,897	$ 21,897	$ 20,907	$ 20,592