US3569852A
Expired / Lapsed
US
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Frequency selective variable gain amplifier
Assignee: American Optical Corp
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Filing: 1969-01-23
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Granted: 1971-03-09
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Expires: 1989-01-23
Abstract
Abstract An amplifier for an electrocardiographic monitoring system. The band-pass of the amplifier is such that ordinarily all frequency components of the ECG signal are amplified to the same extent. In the presence of a low frequency noise signal which causes the output voltage to exceed a maximum limit in either direction, the low frequency 3-db. point is raised from .05 Hertz to 1.0 Hertz. This is achieved simply by lowering the time constant of a high pass filter in the amplifier. The shorter time constant reduces the effect of low frequency noise on the output voltage. While some of the low frequency components in the ECG signal are attenuated, most of the usable information in the signal is retained. The shorter time constant also provides a faster recovery for the amplifier following large direct current voltage changes. This is especially beneficial when the patient electrodes of the monitoring system are switched and they induce a charge in the DC component of the ECG signal which might saturate the ECG preamplifier. Similarly, in the presence of high frequency noise signals the high frequency 3-db. point is lowered for a similar purpose.
Inventors
- 👤 Barouh V Berkovits
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 23:21
CPC Classifications
H; H03; H03F; H03F1/00; H03F1/26; A; A61; A61B; A61B5/00; A61B5/24; A61B5/30; A61B5/307; A61B5/308; A61B5/316; A61B5/318; A61B5/333; A61B5/338; H03G; H03G5/00; H03G5/02; H03G5/14; H03G5/16; H03G5/18; Y; Y10; Y10S; Y10S128/00; Y10S128/901
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
82 words
An electrocardiographic amplifier comprising amplifying means for amplifying an electrocardiographic signal, said amplifying means normally having a constant gain for all frequency components characteristic of said signal, detecting means for detecting the presence and absence of low frequency noise above a predetermined magnitude, and gain lowering and restoring means responsive instantaneously to said detecting means for lowering and restoring a low frequency portion of said gain, said portion corresponding substantially in frequency range to that of said noise, thereby controlling said noise.
Claim 2
Dependent Claim
82 words
An electrocardiographic amplifier comprising amplifying means for amplifying an electrocardiographic signal, said amplifying means normally having a constant gain for all frequency components characteristic of said signal, detecting means for detecting the presence and absence of low frequency noise above a predetermined magnitude, and gain lowering and restoring means responsive instantaneously to said detecting means for lowering and restoring a low frequency portion of said gain, said portion corresponding substantially in frequency range to that of said noise, thereby controlling said noise.
Claim 3
Dependent Claim
33 words
An electrocardiographic amplifier in accordance with claim 1 wherein said detecting means is a bipolarity threshold detector responsive to the magnitude of an output signal of said amplifying means exceeding a predetermined value.
Claim 4
Dependent Claim
72 words
An electrocardiographic amplifier in accordance with claim 1 further including a high-pass filter having a first resistor and a capacitor therein through which said signal is transmitted and wherein said gain lowering and restoring means includes placing means for placing and removing an additional resistor in parallel with said first resistor in said high-pass filter substantially simultaneously with the detection of the presence and absence of said noise above said predetermined magnitude.
Claim 5
Dependent Claim
16 words
An electrocardiographic amplifier in accordance with claim 3 wherein said amplifying means is a DC amplifier.
Claim 6
Dependent Claim
90 words
An electrocardiographic amplifier comprising amplifying means for amplifying an electrocardiographic signal, said amplifying means having output means and normally having a constant gain for all frequency components characteristic of said signal, detecting means for detecting from said output means the presence and absence of high frequency noise above a predetermined magnitude, and gain lowering and restoring means responsive instantaneously to said detecting means for lowering and restoring a high frequency portion of said gain, said portion corresponding substantially in frequency range to that of said noise, thereby controlling said noise.
Claim 7
Dependent Claim
90 words
An electrocardiographic amplifier comprising amplifying means for amplifying an electrocardiographic signal, said amplifying means having output means and normally having a constant gain for all frequency components characteristic of said signal, detecting means for detecting from said output means the presence and absence of high frequency noise above a predetermined magnitude, and gain lowering and restoring means responsive instantaneously to said detecting means for lowering and restoring a high frequency portion of said gain, said portion corresponding substantially in frequency range to that of said noise, thereby controlling said noise.
Claim 8
Dependent Claim
35 words
An electrocardiographic amplifier in accordance with claim 5 wherein said detecting means is a bipolarity threshold detector responsive to the high frequencies in an output signal of said amplifying means exceeding a predetermined threshold level.
Claim 9
Dependent Claim
48 words
An electrocardiographic amplifier in accordance with claim 5 wherein said gain lowering and restoring means includes inserting means for inserting and removing a low-pass filter in the transmission path of said signal simultaneously with the detection of the presence and absence of said noise above said predetermined magnitude.
Claim 10
Dependent Claim
16 words
An electrocardiographic amplifier in accordance with claim 6 wherein said amplifying means is a DC amplifier.
Claim 11
Dependent Claim
29 words
An electrocardiographic amplifier in accordance with claim 5 wherein said detecting means includes means for differentiating said signal and means for comparing the differential signal with a threshold level.
Claim 12
Dependent Claim
129 words
An amplifier comprising amplifying means for amplifying an input signal, said amplifying means having output means and normally having a constant gain for all frequency components characteristic of said signal, determining means for determining from said output means whether an output of said amplifier means exceeds a predetermined value, gain lowering means responsive simultaneously to said determining means for lowering the gain of said amplifying means for selected frequency components characteristic of said signal, a high-pass filter having a first resistor and a capacitor therein through which said input signal is transmitted, and wherein said gain lowering means includes means for placing an additional resistor in parallel with said first resistor in said high-pass filter simultaneously with the determination of the presence of said signal above said predetermined value.
Claim 13
Dependent Claim
129 words
An amplifier comprising amplifying means for amplifying an input signal, said amplifying means having output means and normally having a constant gain for all frequency components characteristic of said signal, determining means for determining from said output means whether an output of said amplifier means exceeds a predetermined value, gain lowering means responsive simultaneously to said determining means for lowering the gain of said amplifying means for selected frequency components characteristic of said signal, a high-pass filter having a first resistor and a capacitor therein through which said input signal is transmitted, and wherein said gain lowering means includes means for placing an additional resistor in parallel with said first resistor in said high-pass filter simultaneously with the determination of the presence of said signal above said predetermined value.
Claim 14
Dependent Claim
33 words
An amplifier in accordance with claim 10 wherein said amplifying means is a DC amplifier and said selected frequency components are at the low end of the frequency spectrum of said input signal.
Claim 15
Dependent Claim
33 words
An amplifier in accordance with claim 10 wherein said determining means includes means for deemphasizing the low frequency components in the output of said amplifying means relative to the high frequency components therein.
Claim 16
Dependent Claim
27 words
An amplifier in accordance with claim 10 wherein said gain lowering means includes means for inserting a low-pass filter in the transmission path of said input signal.
Claim 17
Dependent Claim
27 words
An amplifier in accordance with claim 12 wherein said gain lowering means includes means for inserting a low-pass filter in the transmission path of said input signal.
Claim 18
Dependent Claim
33 words
An amplifier in accordance with claim 12 wherein said amplifying means is a DC amplifier and said selected frequency components are at the high end of the frequency spectrum of said input signal.
Claim 19
Dependent Claim
113 words
An amplifier comprising amplifying means for amplifying an input signal, said amplifying means having output means and normally having a first gain characteristic, detecting means for detecting from said output means the presence of noise interfering with said input signal, and adjusting means responsive instantaneously to said detecting means for adjusting said amplifying means to have a second gain characteristic said second characteristic providing a reduction in interference between said noise and signal, a high-pass filter having a first resistor and a capacitor therein through which said input signal is transmitted, and wherein said adjusting means includes means for placing an additional resistor in parallel with said first resistor in said high-pass filter.
Claim 20
Dependent Claim
113 words
An amplifier comprising amplifying means for amplifying an input signal, said amplifying means having output means and normally having a first gain characteristic, detecting means for detecting from said output means the presence of noise interfering with said input signal, and adjusting means responsive instantaneously to said detecting means for adjusting said amplifying means to have a second gain characteristic said second characteristic providing a reduction in interference between said noise and signal, a high-pass filter having a first resistor and a capacitor therein through which said input signal is transmitted, and wherein said adjusting means includes means for placing an additional resistor in parallel with said first resistor in said high-pass filter.
Claim 21
Dependent Claim
31 words
An amplifier in accordance with claim 16 wherein said detecting means is a thresHold detector responsive to the magnitude of an output signal of said amplifying means exceeding a predetermined value.
Claim 22
Dependent Claim
60 words
An amplifier in accordance with claim 16 further including means for limiting the response of said detecting means to the high frequency components in said input signal relative to the low frequency components therein, and wherein said second gain characteristic has an upper 3-db point which is lower in frequency than the upper 3-db point of said first gain characteristic.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-03-08 | 1974-09-07 | 1975-03-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-03-08 | 1978-09-07 | 1979-03-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-03-08 | 1982-09-07 | 1983-03-09 | $7700.00 | Window Closed / Lapsed |