# US 4,868,774 A · Digital waveform generator and associated method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,868,774 A - Document ID: US4868774A - Status: Granted - Kind: A - Application number: 07/291,199 - Filed: 1988-12-28 - Granted: 1989-09-19 - Earliest claimed: 1985-03-22 - Assignees: Enertec - Inventors: Ferial Beukara - Web page: https://patentgrep.com/patent/US4868774A ## CPC - G06F 1/0321: {Waveform generators, i.e. devices for generating periodical functions of time, e.g. direct digital synthesizers (G06F1/0314, G06F1/035 take precedence)} - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract The present invention relates to synthesis of an analog waveform representative of digital input words but subject to band limiting. In a device for performing such a synthesis a plurality of samples, obtained from the input words by accessing them in memory at a sampling frequency are filtered by a programmable digital filter to yield a plurality of output words which may be fed to a digital to analog converter at a conversion frequency, the converter producing an analog output representative of the input words. ## Claims ### Claim 1 A method for producing from a given series of digital input words, an output in the form of an analog waveform approximating, in analog amplitude with respect to time, values of a notional digital signal that would be formed by stepping through each of said digital input words at a stepping frequency selectable over a range of frequencies between a lower stepping frequency limit and an upper stepping frequency limit, said analog waveform having frequency components not exceeding a limiting frequency, comprising the steps of: deriving a plurality of digital samples from said digital input words, said samples being equivalent to a sampling of said notional digital signal at a sampling frequency which exceeds said stepping frequency; applying said samples to a programmable digital filter arranged to filter said samples to produce a sequence of digital output words, at a predetermined conversion frequency, said conversion frequency being at least twice said limiting frequency and independent of said selected stepping frequency; and converting said output words from digital form to analog form at said conversion frequency to thereby yield said analog waveform as said output. ### Claim 2 (depends on 1) A method according to claim 1 including the step of arranging said digital filter to provide digital output words having a number of bits greater than the number of bits of said digital input words. ### Claim 3 (depends on 1) A method according to claim 1 and including the step of selecting said conversion frequency to be at least four times said stepping frequency. ### Claim 4 (depends on 1) A method according to claim 1 including the step of arranging said digital filter as a low pass filter. ### Claim 5 (depends on 1) A method according to claim 1 and including the step of selecting the number of said digital samples to be greater than the number of digital output words converted. ### Claim 6 (depends on 1) A method according to claim 1 including, as said step of deriving samples, storing said digital input words in a memory and accessing said memory at a later time prior to sampling. ### Claim 7 (depends on 1) A method according to claim 1 including the step of storing the digital output words in a memory and accessing said stored words to repeatedly generate said analog waveform. ### Claim 8 (depends on 1) A method according to claim 1 including the step of, during said step of applying said samples to said digital filter, applying a weighing to said digital samples said weighing being selected to compensate for distortion introduced in conversion of said digital output words. ### Claim 9 (depends on 1) A method according to claim 1 and including the step of smoothing said analog waveform. ### Claim 10 A device for producing, from a given series of digital input words, an output in the form of an analog waveform approximating, in analog amplitude with respect to time, values of a notional digital signal that would be formed by stepping through each of said digital input words at a stepping frequency selectable over a range of frequencies between a lower stepping frequency limit and an upper stepping frequency limit, said analog waveform having frequency components not exceeding a limiting frequency, said device comprising: sampling means for deriving a plurality of digital samples from said digital input words, said samples being equivalent to a sampling of said notional digital signal at a sampling frequency, said sampling frequency exceeding said stepping frequency; a programmable digital filter arranged to filter said samples to produce a sequence of digital output words, at a predetermined conversion frequency, said conversion frequency being at least twice said limiting frequency and independent of said selected stepping frequency, and a digital to analog converter for converting said output words from digital form to analog form at a said conversion frequency to thereby yield said analog waveform as said output. ### Claim 11 (depends on 10) A device according to claim 10 comprising a memory for containing said digital input words and programmable means for accessing said words at a stepping frequency. ### Claim 12 (depends on 11) A device according to claim 11 and wherein said sampling frequency is greater than said conversion frequency. ### Claim 13 (depends on 12) A device according to claim 12 wherein said digital filter produces output words at said sampling frequency and comprising a buffer circuit for supplying selected digital output words to said digital to analog converter at said conversion frequency. ### Claim 14 (depends on 10) A device according to claim 10 wherein said digital to analog converter has a resolution, expressed in number of bits, greater than the number of bits of said digital input words.