US3577087A - Sequence {37 and{38 {0 gate with resetting means - Google Patents

Sequence {37 and{38 {0 gate with resetting means Download PDF

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US3577087A
US3577087A US763196A US3577087DA US3577087A US 3577087 A US3577087 A US 3577087A US 763196 A US763196 A US 763196A US 3577087D A US3577087D A US 3577087DA US 3577087 A US3577087 A US 3577087A
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signal
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charge
transistor
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Thomas B Martin
Henry J Zadell
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RCA Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
    • H03K5/22—Circuits having more than one input and one output for comparing pulses or pulse trains with each other according to input signal characteristics, e.g. slope, integral
    • H03K5/26—Circuits having more than one input and one output for comparing pulses or pulse trains with each other according to input signal characteristics, e.g. slope, integral the characteristic being duration, interval, position, frequency, or sequence
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
    • G10L15/00—Speech recognition

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  • This invention relates to circuits for detecting two sequential events that occur within a given time interval and without another event between them.
  • the phonemes constituting a given word must be detected in a specific sequence for each word of the machines vocabulary.
  • the two sequential phonemes to be recognized are /T/ and /U/.
  • the circuit must not recognize the word TRUE as TOO because of the undesired intervening phoneme /R/.
  • a word ending with the phoneme [I"/ followed by a word beginning with the phoneme /U/ must not be recognized as TOO because of the pause or glottal stop between words.
  • a circuit stores a charge when a first signal occurs. When a second signal occurs, an output is produced if the charge is being stored. The stored charge will be discharged by a third signal if it occurs prior to the time of the occurrence of the second signal.
  • FIG. 1 is a schematic of the preferred embodiment of the invention.
  • FIG. 2 is a diagram illustrating the shapes of signals at various points in the schematic identified by upper case letters.
  • An enabling input in FIG. I is connected to a source of signals indicative of a first desired event, e.g., a /T/ phoneme.
  • a phoneme separator 12 will produce a positive square pulse whenever the input speech picked up by a microphone 14 contains a /T/ phoneme.
  • a disabling input 16 will receive a positive square pulse from another phoneme separator 18 whenever the input speech contains an /R/ phoneme.
  • a gating input 20 will receive a positive square pulse from the phoneme separator 22 whenever a /U/ phoneme occurs in the input speech.
  • the output 24 produces a negative pulse whenever the spoken word TOO (including T0 or TWO) occurs in the input speech.
  • FIG. 2 line A, represents the signal to the enabling input 10; FIG. 2, line C, the signal to the disabling input 16; and FIG. 2, line E, the signal to the gating input 20.
  • the first word represented is T00 and the second is TRUE.
  • the signal applied to the input 10 is differentiated by a series RC circuit consisting of the capacitor 26 and the resistor 28 so that only trigger-shaped spikes tend to appear at the emitter 52 of the transistor 30.
  • the diode 32 suppresses the positive spikes 'so that only negative spikes actually appear at the emitter 52.
  • FIG. 2, line B illustrates the signal shape with the suppressed positive spikes shown by dotted lines.
  • the transistor 30 is biased so the quiescent current maintains the base of the transistor 34 in the active region.
  • the negative spike appearing at the emitter 52 acts to cutoff transistor 30 which reduces'the current in transistor 34 causing the voltageat the collector 56 to rise toward rl-V.
  • the negative spike also causes the capacitor 36 to discharge through the resistor 38.
  • the signal at the base of the transistor 34 (and collector of the transistor 30) is shown in FIG. 2, line F the slope of the negative-going edge at time tj is determined by the RC constant of the resistor 38 and the capacitor 36 in FIG. 1. After the emitter 52 returns to its quiescent voltage, the capacitor 36 begins to charge through the transistor 30. The RC time constant for this charging rate is determined by the output impedance of the transistor 30 in combination with the resistor 38 and the value of the capacitor 36. Because of feedback from the emitter 60 of the transistor 58 which is covered in more detail below, the effect of the signal at the base of the transistor 34 is the waveshape depicted by the dotted line 41 in FIG. 2, line F.
  • the transistors 34 and 42 form a difference amplifier.
  • the transistor 44 and its biasing resistors 46, 48 and 50, constitute a constant current source 45 for the transistors 34 and 42.
  • the voltage at the collector 56 rises toward +V as described above and increases the current through the transistor 58,
  • FIG. 2 shows the voltage waveshape across the capacitor 76.
  • the negative-going edge has a time constant that is dependent both on the RC value of the capacitor 76 and the resistor 78 and on the signal waveshape at the emitter 60 of the transistor 58.
  • the positive-going edge of the waveshape shown in FIG. 2, line G, at t, and 1 is fast rising because of the regenerative feedback from the emitter 60.
  • the signal at the base 80 of the transistor 82 is amplified by two stages consisting of the transistors 82 and 84 and their biasing resistors.
  • the collector of the transistor 82 is clamped to ground by the diode 86.
  • the amplification of the signal by the transistor 82 si sufficient either to saturate or to cut off the transistor 84 between the highest and lowest voltages, respectively, at the collector of the transistor 82.
  • the output of the transistor 84 is a step function as shown in FIG. 2, line H.
  • T00 and output from the phoneme separator 22 follows the output from the phoneme separator 12 and is applied to the gating input 20.
  • the input to the diode 96 is shown in FIG. 2, line H, and the input to diode 98 is shown in FIG.
  • FIG. 2 line E, which is the output of the phoneme separator 22 applied to the gating input 20.
  • FIG. 2, line I illustrates the voltage waveshape of the output 24.
  • the negative square pulse 100 v The negative-going edge 85 of the signal depicted in FIG. 2, line G, decreases in time to a value less than that required to keep the transistor M cutoff, at which point, time 2 the transistor 84 is turned on causing the input signal to the diode as to approach ground thereby inhibiting a signal at the output 24 if a positive signal to the gating input 20 subsequently occurs. This time-dependence prevents recognition of widely spaced [TI and /U/ phonemes as a single word.
  • the IR/ phoneme follows the /T/ phoneme and precedes the IU/ phoneme.
  • the following description will illustrate how an outputis inhibited by the occurrence of the intervening /R/ phoneme.
  • the [TI phoneme signal at the input causes a cycle of operation that is identical to that described above, i.e., time of FIG. 2 corresponds to time t,, until the occurrence of the negative edge of the IR/ phoneme pulse at the input 16 at time t,,.
  • the waveshape at the emitter 72 of the transistor 62 caused by the input signal from the phoneme separator 18 is illustrated in FIG. 2, line D.
  • the result is a circuit operation analogous to that described above for the signal occurring at the emitter 52 of the transistor 30.
  • the feedback from the emitter 60 becomes regenerative because it no longer affects the transistor 30, thereby causing a sharp drop in the emitter 60 voltage and consequently that at the emitter of the transistor 74.
  • the capacitor 76 discharges through the resistor 78 turning off the transistor 82 and turning on the transistor 84.
  • the input to the diode 96 is close to ground, inhibiting an output from the transistor 88 when the phoneme separator 22 applies an input pulse at time t, to the gating input 20.
  • input means responsive to a first signal for storing a charge indicative of the occurrence of said first signal; coincidence gating means responsive to a third signal and the charge being stored for producing anoutput isolated from said input means;
  • first charge storage means responsive to a first signal for storing a charge representing the occurrence of said first signal
  • second charge storage means responsive to a second signal for storing a charge representing the occurrence of said second signal
  • first and second input stages each having input means, output means, and charging means for maintaining an output signal for a predetermined time interval after removal of an input signal for the stage;
  • differencing means having an output means and first and second input means, for producing an output according to the difference between the signals applied to said first and second input means thereof; gating means, having first and second input means, for

Abstract

Circuit for sensing two signals and producing an output when the signals are in sequence, with resetting means to inhibit the output after a specific time interval has elapsed between the two signals or whenever an intervening other signal occurs.

Description

United States Patent Inventors Thomas B. Martin Delran; Henry J. Zadell, Haddoniield, NJ. App]. No. 763,196 Filed Sept. 27, 1968 Patented May 4, 1971 Assignee Radio Corporation of America SEQUENCE AND GATE WITH RESETTING MEANS 6 Claims, 2 Drawing Figs. US. Cl 328/110, 179/1, 307/232, 307/234, 307/246, 328/119 Int. Cl H03k 5/20 Field of Search 307/201,
[56] References Cited UNITED STATES PATENTS 2,962,551 1 1/1960 Johanneson 307/242X 3,1 19,027 1/1964 Faust 307/293 3,132,263 5/1964 Maass..... 307/293X 3,344,233 9/1967 Tufts 179/1 Primary Examiner-Stanley D. Miller, Jr. Attorney-H. Christoffersen ABSTRACT: Circuit for otting means two signals and producing an output when the signals are in sequence, with resetting means to inhibit the output after a specific time interval has elapsed between the two signals or whenever an intervening other signal occurs.
L 55,97 I 9z PATENIED HAY 41ml ,SHEEI 1 OF 2 ATTORNEY SEQUENCE AND GATE WITH RESETTING MEANS BACKGROUND OF THE INVENTION This invention relates to circuits for detecting two sequential events that occur within a given time interval and without another event between them. For example, in speech recogni- 7 tion circuits of the type deriving phonemes from input speech, the phonemes constituting a given word must be detected in a specific sequence for each word of the machines vocabulary. In a machine with a vocabulary word TOO (T or TWO), the two sequential phonemes to be recognized are /T/ and /U/. The circuit must not recognize the word TRUE as TOO because of the undesired intervening phoneme /R/. Furthermore, a word ending with the phoneme [I"/ followed by a word beginning with the phoneme /U/ must not be recognized as TOO because of the pause or glottal stop between words.
It is an object of this invention to provide a simple sequential event detector which is reset by intervening undesired events or by an excessive time interval between the desired events.
BRIEF SUMMARY OF THE INVENTION A circuit stores a charge when a first signal occurs. When a second signal occurs, an output is produced if the charge is being stored. The stored charge will be discharged by a third signal if it occurs prior to the time of the occurrence of the second signal.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of the preferred embodiment of the invention.
FIG. 2 is a diagram illustrating the shapes of signals at various points in the schematic identified by upper case letters.
DETAILED DESCRIPTION OF THE INVENTION The operation of the preferred embodiment of the invention shown in FIG. 1 will be explained in conjunction with the waveshape diagram of FIG. 2 and, for purposes of illustration, terms of differentiating between the spoken words T00 and RUE.
An enabling input in FIG. I is connected to a source of signals indicative of a first desired event, e.g., a /T/ phoneme. A phoneme separator 12 will produce a positive square pulse whenever the input speech picked up by a microphone 14 contains a /T/ phoneme. A disabling input 16 will receive a positive square pulse from another phoneme separator 18 whenever the input speech contains an /R/ phoneme. A gating input 20 will receive a positive square pulse from the phoneme separator 22 whenever a /U/ phoneme occurs in the input speech. The output 24 produces a negative pulse whenever the spoken word TOO (including T0 or TWO) occurs in the input speech.
FIG. 2, line A, represents the signal to the enabling input 10; FIG. 2, line C, the signal to the disabling input 16; and FIG. 2, line E, the signal to the gating input 20. The first word represented is T00 and the second is TRUE.
The signal applied to the input 10 is differentiated by a series RC circuit consisting of the capacitor 26 and the resistor 28 so that only trigger-shaped spikes tend to appear at the emitter 52 of the transistor 30. The diode 32 suppresses the positive spikes 'so that only negative spikes actually appear at the emitter 52. FIG. 2, line B, illustrates the signal shape with the suppressed positive spikes shown by dotted lines. The transistor 30 is biased so the quiescent current maintains the base of the transistor 34 in the active region. The negative spike appearing at the emitter 52 acts to cutoff transistor 30 which reduces'the current in transistor 34 causing the voltageat the collector 56 to rise toward rl-V. The negative spike also causes the capacitor 36 to discharge through the resistor 38. The signal at the base of the transistor 34 (and collector of the transistor 30) is shown in FIG. 2, line F the slope of the negative-going edge at time tj is determined by the RC constant of the resistor 38 and the capacitor 36 in FIG. 1. After the emitter 52 returns to its quiescent voltage, the capacitor 36 begins to charge through the transistor 30. The RC time constant for this charging rate is determined by the output impedance of the transistor 30 in combination with the resistor 38 and the value of the capacitor 36. Because of feedback from the emitter 60 of the transistor 58 which is covered in more detail below, the effect of the signal at the base of the transistor 34 is the waveshape depicted by the dotted line 41 in FIG. 2, line F.
The transistors 34 and 42 form a difference amplifier. The transistor 44 and its biasing resistors 46, 48 and 50, constitute a constant current source 45 for the transistors 34 and 42.
The voltage at the collector 56 rises toward +V as described above and increases the current through the transistor 58,
causing the emitter 60 voltage to rise toward +V. This positive increase at the emitter 60 furnishes feedback current to the transistors 30 and 62 through the resistors 64 and 66, respectively. The amount of feedback to the transistor 62 is initially greater than that to the transistor 30 because of the diodes 68 and 70 in series with the resistor 64. In order for the feedback current to reach the emitter 52, the voltage of the feedback must increase sufficiently to forward-bias the diodes 68 and 70. The feedback current reaching the emitter 72 causes the current through the transistor 62 to increase and consequently, the current through the transistor 42 to increase. Because the total current through both transistors 34 and 42 is a fixed value determined by the constant current source 45, an increase of current through the transistor 42 results in a decrease of current through the transistor 34 which in turn causes the collector 56 voltage to rise more toward +V. The feedback from the emitter 60 to the emitters 52 and 72 is, therefore, regenerative until the combines threshold voltages of the diodes 68 and 70 are exceeded. Thereafter, the effect of the feedback is cancelled because any tendency to increase current in either transistor 34 or 42 is countered by an equal tendency in the other. As a result, the feedback loop causes a sharp rise in the voltage in the emitter 60 for a small input signal.
The increase of voltage at the emitter 60 increases the current through the transistor 74, which in turn increases the voltage across the capacitor 76 and at the base of the transistor 82. The capacitor 76 provides additional holding in the circuit at the base 80. FIG. 2, line G, shows the voltage waveshape across the capacitor 76. The negative-going edge has a time constant that is dependent both on the RC value of the capacitor 76 and the resistor 78 and on the signal waveshape at the emitter 60 of the transistor 58. The positive-going edge of the waveshape shown in FIG. 2, line G, at t, and 1 is fast rising because of the regenerative feedback from the emitter 60.
The signal at the base 80 of the transistor 82 is amplified by two stages consisting of the transistors 82 and 84 and their biasing resistors. The collector of the transistor 82 is clamped to ground by the diode 86. The amplification of the signal by the transistor 82 si sufficient either to saturate or to cut off the transistor 84 between the highest and lowest voltages, respectively, at the collector of the transistor 82. The output of the transistor 84 is a step function as shown in FIG. 2, line H.
In the first word, T00, and output from the phoneme separator 22 follows the output from the phoneme separator 12 and is applied to the gating input 20. The transistor 88, the biasing resistors 90, 92 and 94, and the input diodes 96 and 98 form a logical NAND gate that produces an approximately zero output voltage at the output 24 whenever positive signals of nearly +V volts are applied to both input diodes 96 and 98 simultaneously and an output voltage approaching +V whenever a signal of approximately zero volts is applied to either diode 96 or 98. The input to the diode 96 is shown in FIG. 2, line H, and the input to diode 98 is shown in FIG. 2, line E, which is the output of the phoneme separator 22 applied to the gating input 20. FIG. 2, line I, illustrates the voltage waveshape of the output 24. The negative square pulse 100 v The negative-going edge 85 of the signal depicted in FIG. 2, line G, decreases in time to a value less than that required to keep the transistor M cutoff, at which point, time 2 the transistor 84 is turned on causing the input signal to the diode as to approach ground thereby inhibiting a signal at the output 24 if a positive signal to the gating input 20 subsequently occurs. This time-dependence prevents recognition of widely spaced [TI and /U/ phonemes as a single word.
In the second word, beginning at time L on FIG. 2, the IR/ phoneme follows the /T/ phoneme and precedes the IU/ phoneme. The following description will illustrate how an outputis inhibited by the occurrence of the intervening /R/ phoneme.
The [TI phoneme signal at the input causes a cycle of operation that is identical to that described above, i.e., time of FIG. 2 corresponds to time t,, until the occurrence of the negative edge of the IR/ phoneme pulse at the input 16 at time t,,. The waveshape at the emitter 72 of the transistor 62 caused by the input signal from the phoneme separator 18 is illustrated in FIG. 2, line D. The result is a circuit operation analogous to that described above for the signal occurring at the emitter 52 of the transistor 30. As the voltage at the base of the transistor 42 decreases, more current flows through the transistor 34 (because of the constant current source 4l5 as explained above) so that the collector 56 voltage is decreased. This, in turn, causes the voltage at the emitter 60 to approach ground, and a negative-going signal is fed back via the resistors 66 and 64. Because the feedback diodes 6d and 70 are forward-biased from action of the IT/ phoneme, the feedback from the emitter 60 is applied equally to the emitters of the transistors 30 and 62. The voltage at the emitter 6419 of the transistor 58 decreases because of the decrease in voltage at the collector 56 of the transistor as. When the voltage at the' emitter so has decreased to the point where the diodes 68 and 70 are no longer forward-biased, the feedback from the emitter 60 becomes regenerative because it no longer affects the transistor 30, thereby causing a sharp drop in the emitter 60 voltage and consequently that at the emitter of the transistor 74. The capacitor 76 discharges through the resistor 78 turning off the transistor 82 and turning on the transistor 84. The input to the diode 96 is close to ground, inhibiting an output from the transistor 88 when the phoneme separator 22 applies an input pulse at time t, to the gating input 20. The use of several stages of amplification and biasing the leading stages in the active region permits use of the described circuit in applications where the input signals are small. It is apparent to those skilled in the art that the input signals need not be differentiated and the positive-going signals can be utilized to perfonn different timing functions. It is also apparent that with sufficiently large input signals, several of the stages shown in FIG. 1 can be eliminated.
We claim:
1. The combination comprising:
input means responsive to a first signal for storing a charge indicative of the occurrence of said first signal; coincidence gating means responsive to a third signal and the charge being stored for producing anoutput isolated from said input means; and
means responsive to the occurrence of a second signal, prior to the third signal, for discharging said stored charge.
2. The combination as claimed in claim 1 including means for discharging said stored charge within a predetermined time interval after the occurrence of said first signal.
3. The combination comprising:
first charge storage means responsive to a first signal for storing a charge representing the occurrence of said first signal; second charge storage means responsive to a second signal for storing a charge representing the occurrence of said second signal; a
means responsive to said first and second charge storage means for producing an enabling signal whenever said first charge storage means is storing a charge and the second charge storage means is not; and coincidence gating means responsive to a third signal and said enabling signal for producing an output.
4. The combination as claimed in claim 3 including means for discharging said stored charges in a predetermined interval of time.
5. The combination comprising:
first and second input stages, each having input means, output means, and charging means for maintaining an output signal for a predetermined time interval after removal of an input signal for the stage;
differencing means, having an output means and first and second input means, for producing an output according to the difference between the signals applied to said first and second input means thereof; gating means, having first and second input means, for
producing an output whenever signals are applied simultaneously to said first and second input means of said gating means;
means for coupling a first signal to the input means of said first input stage;
means for coupling a second signal to the input means of said second input stage;
means for coupling a third signal to the second input means of said gating means;
means coupling the output means of said first input stage to the first input means of said differencing means;
means coupling the output means of said second input stage to the first input means of said differencing means; and means coupling the output means of said differencing means to the first input means of said gating means.
6. The'combination as claimed in claim 5 including feedback means coupled between the output of the differencing means and the input means of said first and second input stages.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 577 O87 Dated 4 19 71 Inventor(s) Thomas B. Martin 5 Henry J. Zadell It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
In the Abstract, first line, delete "otting means" and inse therefor sensing Column 2, line 56, "si" should read is Column 3, line 9, after "time" insert t Column 4, line 30, "for" should read frm Signed and sealed this 15th day of February 1972.
(SEAL) Attest:
EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims (6)

1. The combination comprising: input means responsive to a first signal for storing a charge indicative of the occurrence of said first signal; coincidence gating means responsive to a third signal and the charge being stored for producing an output isolated from said input means; and means responsive to the occurrence of a second signal, prior to the third signal, for discharging said stored charge.
2. The combination as claimed in claim 1 including means for discharging said stored charge within a predetermined time interval after the occurrence of said first signal.
3. The combination comprising: first charge storage means responsive to a first signal for storing a charge representing the occurrence of said first signal; second charge storage means responsive to a second signal for storing a charge representing the occurrence of said second signal; means responsive to said first and second charge storage means for producing an enabling signal whenever said first charge storage means is storing a charge and the second charge storage means is not; and coincidence gating means responsive to a third signal and said enabling signal for producing an output.
4. The combination as claimed in claim 3 including means for discharging said stored charges in a predetermined interval of time.
5. The combination comprising: first and second input stages, each having input means, output means, and charging means for maintaining an output signal for a predetermined time interval after removal of an input signal for the stage; differencing means, having an output means and first and second input means, for producing an output according to the difference between the signals applied to said first and second input means thereof; gating means, having first and second input means, for producing an output whenever signals are applied simultaneously to said first and second input means of said gating means; means for coupling a first signal to the input means of said first input stage; means for coupling a second signal to the input means of said second input stage; means for coupling a third signal to the second input means of said gating means; means coupling the output means of said first input stage to the first input means of said differencing means; means coupling the output means of said second input stage to the first input means of said differencing means; and means coupling the output means of said differencing means to the first input means of said gating means.
6. The combination as claimed in claim 5 including feedback means coupled between the output of the differencing means and the input means of said first and second input stages.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4063031A (en) * 1976-04-19 1977-12-13 Threshold Technology, Inc. System for channel switching based on speech word versus noise detection
US4117348A (en) * 1977-07-11 1978-09-26 Rockwell International Corporation Multi-phase clock monitor circuit
US4894626A (en) * 1988-09-30 1990-01-16 Advanced Micro Devices, Inc. Variable length shift register
US5537064A (en) * 1993-01-08 1996-07-16 National Semiconductor Corp. Logic circuit capable of handling large input current

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2962551A (en) * 1958-01-06 1960-11-29 Bell Telephone Labor Inc Switching circuit
US3119027A (en) * 1960-04-01 1964-01-21 Code A Phone Electronics Inc Signal actuated control circuit
US3132263A (en) * 1961-12-20 1964-05-05 Gen Precision Inc Pulse time selector with minimum delay time
US3344233A (en) * 1967-09-26 Method and apparatus for segmenting speech into phonemes

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3344233A (en) * 1967-09-26 Method and apparatus for segmenting speech into phonemes
US2962551A (en) * 1958-01-06 1960-11-29 Bell Telephone Labor Inc Switching circuit
US3119027A (en) * 1960-04-01 1964-01-21 Code A Phone Electronics Inc Signal actuated control circuit
US3132263A (en) * 1961-12-20 1964-05-05 Gen Precision Inc Pulse time selector with minimum delay time

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4063031A (en) * 1976-04-19 1977-12-13 Threshold Technology, Inc. System for channel switching based on speech word versus noise detection
US4117348A (en) * 1977-07-11 1978-09-26 Rockwell International Corporation Multi-phase clock monitor circuit
DE2830436A1 (en) * 1977-07-11 1979-01-18 Rockwell International Corp MULTI-PHASE CLOCK MONITORING CIRCUIT
US4894626A (en) * 1988-09-30 1990-01-16 Advanced Micro Devices, Inc. Variable length shift register
US5537064A (en) * 1993-01-08 1996-07-16 National Semiconductor Corp. Logic circuit capable of handling large input current
US5546260A (en) * 1993-01-08 1996-08-13 National Semiconductor Corporation Protection circuit used for deactivating a transistor during a short-circuit having an inductive component

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