# US 4,394,743 A · Tone generation method and apparatus using stored reference calibration coefficients > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,394,743 A - Document ID: US4394743A - Status: Granted - Kind: A - Application number: 06/217,678 - Filed: 1980-12-18 - Granted: 1983-07-19 - Earliest claimed: 1980-12-18 - Assignees: Bell Telephone Laboratories, Incorporated - Inventors: Paul A. Mercer - Web page: https://patentgrep.com/patent/US4394743A ## CPC - H04M 1/505: {signals generated in digital form} - H04M: TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08) ## Abstract A tone generator operates in a multiplicative (19) manner with respect to a reference signal (20) for providing a selectable sequence of tones. A digital calibration coefficient is constructed for at least one tone for modifying (22) the reference signal to a value that produces a predetermined output amplitude for the tone. The coefficient is stored (16) for subsequent recall each time the predetermined output amplitude for the tone is required. ## Claims ### Claim 1 A tone signal generator including a source (16) of selectable sets of digital coefficient signals defining a predetermined analog signal waveform, and means (19) for multiplying said coefficient signals by a reference signal for producing an analog tone signal which is recurrent at a predetermined rate, the generator comprising means (53, 13) for feeding back the output of said generator to control the magnitude of said reference signal for establishing a predetermined generator output tone amplitude. ### Claim 2 (depends on 1) The generator in accordance with claim 1 in which said feedback means comprises means (53), responsive to said recurrent analog signal, for generating an error signal which is indicative of the recurrent analog signal amplitude with respect to an additional reference, means (13), responsive to said error signal, for producing a calibration signal, and means (22), responsive to the calibration signal, for modifying the multiplying means reference signal in a direction tending to change the output tone amplitude toward the predetermined amplitude. ### Claim 3 (depends on 2) The generator in accordance with claim 2 in which said generating means includes means for producing a digital error signal having one or the other of two binary signal states, and said modifying means includes means responsive to said digital error signal for modifying the multiplying reference signal in a direction tending to change the state of said error signal. ### Claim 4 (depends on 2) The generator in accordance with claim 2 in which said source produces coefficient signal sets for plural selectable tones in a predetermined frequency range, said calibration signal producing means includes means for producing one calibration signal for said frequency range, and means for applying said one calibration signal in said modifying means for each of said plural tones. ### Claim 5 (depends on 2) The generator in accordance with claim 2 in which said source produces coefficient signal sets for plural selectable tones in a predetermined frequency range, and said calibrating signal producing means includes means for producing at least two different calibration signals for different parts, respectively, of said range, and means for applying each of said calibration signals in said modifying means for tones in said respective different parts of said frequency range. ### Claim 6 (depends on 2) The generator in accordance with claim 2 in which said source produces coefficient signal sets for plural selectable tones in a predetermined frequency range, and said calibrating signal producing means includes means for producing plural calibration signals for at least one of said tones, and means for applying each of said calibration signals for a tone in said modifying means for a different time part of the generation of such tone during the operation of said generator. ### Claim 7 (depends on 2) The generator in accordance with claim 2 in which said source produces coefficient signal sets for plural selectable tones in a predetermined frequency range, and said calibration signal producing means includes means for producing plural calibration signals for at least one of said tones, and means for applying each of said plural calibration signals for a tone in said modifying means for a different selectable generation of such tone in the operation of said generator. ### Claim 8 (depends on 2) The tone generator in accordance with claim 2 in which said modifying means further comprises a calibrating MDAC (22) connected for providing said multiplying means reference signal, and a low temperature coefficient analog reference signal source (23) connected to provide a stable analog reference to said calibrating MDAC, said reference signal source having a much lower temperature coefficient of output voltage than other elements of said tone generator. ### Claim 9 (depends on 2) The tone generator in accordance with claim 2 in which said multiplying means comprises a generating, multiplying, digital-to-analog converter (19) (MDAC), and said calibration signal producing means comprises means (13) for processing signals to produce said calibration signal and memory means (16) for storing said calibration signal. ### Claim 10 (depends on 9) The tone generator in accordance with claim 9 in which said processing means comprises means for executing a successive approximation process in response to said error signal for setting, as said calibration signal, respective digits of a digital reference coefficient signal, and means for storing said digital reference coefficient signal in said memory means to be subsequently called during an output tone generating sequence. ### Claim 11 (depends on 9) The tone generator in accordance with claim 9 in which said processing means includes stored program control means for controlling said memory means to supply selectable coefficient sets to said generating MDAC to cause the output therefrom to include a predetermined series of tones and for correspondingly sequentially modifying said multiplying reference signal. ### Claim 12 (depends on 11) The tone generator in accordance with claim 11 in which there are provided a bidirectional circuit (10) for outputting tone signals produced by said generator and for receiving command signals for said generator, and means (43) for applying said command signals to an input of said processing means for controlling tone series selection in such processing means. ### Claim 13 (depends on 12) The tone generator in accordance with claim 12 in which said command signal applying means comprises means for suppressing noise in a predetermined amplitude range less than the range of said command signals. ### Claim 14 (depends on 13) The tone generator in accordance with claim 13 in which said command signals are tone bursts of coded durations, said noise suppressing means comprises an amplitude comparator with hysteresis, and said processing means comprises means for providing clock pulses, means for counting processing means clock pulses between output signal level transitions from said amplitude comparator, means for comparing output from said counting means to a predetermined threshold value which is indicative of the frequency of said command signals, and means, responsive to the output of said count comparing means, for decoding detected tone burst durations to control said processing means for tone series selection. ### Claim 15 An analog signal tone generator including a source (12) of at least one set of digital coefficient signals defining an analog waveform of predetermined configuration, and means (19), having an analog reference signal input and responsive to said coefficient signals, for producing said analog signal tone, the generator comprising means (53), responsive to said analog signal tone, for generating a digital error signal indicating a difference in magnitude between said tone and a predetermined reference, and means (13, 22), responsive to said digital error signal, for modifying said analog reference signal to reduce the magnitude of said difference. ### Claim 16 A method for generating at least one tone having a predetermined output amplitude, the method using a multiplication process with respect to a reference signal and comprising the steps of operating the process to produce tone output of uncalibrated amplitude, constructing in response to said tone output a calibrating signal having a value which, when applied to modify said reference signal, causes said uncalibrated amplitude tone output to assume said predetermined output amplitude for such tone, and modifying said reference signal in response to said calibrating signal. ### Claim 17 (depends on 16) The method in accordance with claim 16 comprising the additional steps of storing said calibrating signal for recall, and recalling said stored calibrating signal to modify said reference signal each time that said one tone is generated. ### Claim 18 (depends on 16) The method in accordance with claim 16 in which a plurality of said tones are to be generated in a predetermined series and having, respectively, at least one predetermined output amplitude, the method further comprising the steps of executing said operating and constructing steps for each of said tones to produce corresponding calibrating signals therefor, storing said calibrating signals, and thereafter, when each of said tones is to be generated in said series, recalling its corresponding calibrating signal and executing said modifying step using the recalled signal.