# US 5,349,254 A · Call progress detection circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,349,254 A - Document ID: US5349254A - Status: Granted - Kind: A - Application number: 08/158,148 - Filed: 1993-11-24 - Granted: 1994-09-20 - Earliest claimed: 1992-08-06 - Assignees: Matsushita Electric Corporation of America - Inventors: Dursun Sakarya - Web page: https://patentgrep.com/patent/US5349254A ## CPC - H04M 1/82: Line monitoring circuits for call progress or status discrimination {(for detecting caller identity H04M1/573)} - H04Q 1/444: with voice-band signalling frequencies - H04Q 1/46: comprising means for distinguishing between a signalling current of predetermined frequency and a complex current containing that frequency, e.g. speech current - H04M: TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08) - H04Q: SELECTING (switches, relays, selectors H01H; wireless communication networks H04W) ## Abstract A call progress detection circuit filters the audio input along parallel bandpass and band reject paths. The relevant band of frequencies is defined by the range of 350-620 Hz, within which band all of the call progress tones are found. The energy output from the bandpass path is compared to the energy output from the band reject path to determine if the audio input is generated by a call progress tone or by vocal input. ## Claims ### Claim 1 A signal detection system comprising: at least one first filter means for allowing transmission of signals having energy in a first range of frequencies; at least one second filter means for allowing transmission of signals having energy which is not is said first range of frequencies; means for converting the output of said at least one first and said at least one second filter means from alternating current to direct current; and at least one first means for comparing the output of said at least one first filter means to the output of said at least one second filter means. ### Claim 2 (depends on 1) The signal detection system of claim 1 wherein said at least one first means for comparing said outputs of said at least one first and said at least one second filters comprises at least one differential amplifier. ### Claim 3 (depends on 2) The signal detection system of claim 2 wherein the outputs of said at least one first filter means are provided to the positive inputs of said at least one differential amplifier and the outputs of said at least one second filter means are provided to the negative inputs of said at least one differential amplifier. ### Claim 4 (depends on 1) The signal detection system of claim 1 wherein said at least one first filter means comprises at least one low pass filter and wherein said at least one second filter means comprises at least one high pass filter. ### Claim 5 (depends on 1) The signal detection system of claim 1 wherein said at least one means for comparing said outputs of said at least one first and at least one second filters comprises at least one divider circuit. ### Claim 6 (depends on 1) The signal detection system of claim 1 wherein said at least one first filter means comprises at least one bandpass filter having a frequency range of 350-620 Hz. ### Claim 7 (depends on 6) The signal detection system of claim 6 wherein said at least one second filter means comprises at least one band reject filter having a frequency range of 350-620 Hz. ### Claim 8 (depends on 1) The signal detection system of claim 1 further comprising at least one low pass filter means for outputting at least one average energy value for the direct current outputs of said at least one first and said at least one second filter means. ### Claim 9 (depends on 8) The signal detection system of claim 8 wherein said at least one low pass filter means comprises at least one first low pass filter means associated with said at least one first filter means and at least one second low pass filter means associated with said at least one second filter means. ### Claim 10 (depends on 9) The signal detection system of claim 9 further comprising at least one means for trimming the gain on the output of said at least one first low pass filter means. ### Claim 11 (depends on 10) The signal detection system of claim 10 wherein said at least one means for trimming the gain on the output of said at least one first low pass filter comprises at least one voltage divider connected between said at least one first low pass filter means and said at least one means for comparing. ### Claim 12 (depends on 1) The signal detection system of claim 1 wherein said at least one means for converting comprises at least one first means for converting the outputs of said at least one first filter means and at least one second means for converting the outputs of said at least one second filter means. ### Claim 13 (depends on 1) The signal detection system of claim 1 further comprising at least one second means for comparing which compares the output of said at least one first means for comparing to at least one reference voltage. ### Claim 14 (depends on 13) The signal detection system of claim 13 further comprising: means for dynamically adjusting the at least one reference voltage in proportion to the peak values of the outputs of said at least one first filter means. ### Claim 15 (depends on 1) The signal detection system of claim 1 wherein said at least one first means for comparing comprises at least one multiplier/divider circuit. ### Claim 16 (depends on 1) The signal detection system of claim 1 wherein said range of frequencies comprises the range from 350-620 Hz. ### Claim 17 (depends on 16) The signal detection system of claim 16 wherein said at least one first means for comparing comprises a plurality of comparison circuits each centered about a different frequency in said frequency range. ### Claim 18 (depends on 16) The signal detection system of claim 16 wherein said at least one first filter means comprises a plurality of bandpass filters each centered on a different frequency in said range of frequencies. ### Claim 19 (depends on 16) The signal detection system of claim 16 wherein said at least one second filter means comprises a plurality of notch filters. ### Claim 20 A method for determining if an input signal is within a range of frequencies comprising: providing said signal to at least one first filter means having at least one pass band in said range of frequencies; providing said signal to at least one second filter means having at least one reject band in said range of frequencies; converting the outputs of said filters to direct current; and comparing the converted outputs of said at least one first filter means to the converted outputs of said at least one second filter means. ### Claim 21 (depends on 20) The method of claim 20 wherein said providing of said signal to said at least one first and second filters is simultaneous. ### Claim 22 (depends on 20) The method of claim 20 wherein said comparing of the outputs of said filters comprises providing said outputs to at least one differential amplifier. ### Claim 23 (depends on 22) The method of claim 22 wherein said providing comprises: providing the outputs of said at least one first filter to the positive inputs of said at least one differential amplifier; and providing the outputs of said at least one second filter to the negative inputs of said at least one differential amplifier. ### Claim 24 (depends on 23) The method of claim 23 further comprising trimming the gain of the outputs of said at least one first filter prior to said comparing. ### Claim 25 (depends on 23) The method of claim 23 further comprising the step of comparing the outputs of said at least one differential amplifier to at least one reference voltage. ### Claim 26 (depends on 25) The method of claim 25 further comprising dynamically adjusting said at least one reference voltage. ### Claim 27 (depends on 26) The method of claim 26 wherein said dynamically adjusting of said at least one reference voltage comprises the steps of: detecting at least one peak value of the outputs of said at least one first filter means; and adjusting said at least one reference voltage to a predetermined proportion of said at least one detected peak. ### Claim 28 (depends on 22) The method of claim 22 wherein said comparing comprises the steps of: combining the converted outputs of said at least one first filter means and providing the combined first output to the positive inputs of said at least one differential amplifier; combining the converted outputs of said at least one second filter means and providing the combined second output to the negative inputs of said at least one differential amplifier; and subtracting said combined second output from said combined first output. ### Claim 29 (depends on 28) The method of claim 28 wherein said comparing comprises providing said combined first and second outputs to at least one divider circuit. ### Claim 30 (depends on 28) The method of claim 28 wherein said comparing comprises providing said combined first and said combined second outputs to a plurality of comparison circuits. ### Claim 31 (depends on 30) The method of claim 30 wherein each of said plurality of comparison circuits is centered about a different frequency in said range of frequencies. ### Claim 32 (depends on 20) The method of claim 20 wherein said comparing of the output of said filters comprises providing said outputs to at least one divider circuit. ### Claim 33 (depends on 32) The method of claim 32 further comprising the step of comparing the outputs of said at least one divider circuit to at least one reference voltage. ### Claim 34 (depends on 33) The method of claim 33, further comprising dynamically adjusting said at least one reference voltage. ### Claim 35 (depends on 34) The method of claim 34 wherein said dynamically adjusting of said at least one reference voltage comprises the steps of: detecting at least one peak value of the outputs of said at least one first filter means; and adjusting said at least one reference voltage to a predetermined proportion of said at least one detected peak. ### Claim 36 (depends on 20) The method of claim 20 further comprising averaging said direct current output prior to said comparing. ### Claim 37 (depends on 20) The method of claim 20 further comprising characterizing the output of said comparing means. ### Claim 38 (depends on 20) The method of claim 20 wherein said comparing comprises the steps of: combining the converted outputs of said at least one first filter means; combining the converted outputs of said at least one second filter means; and comparing the combined first filter outputs to the combined second filter outputs.