| 摘要 |
1,266,396. Automatic gain control. AMERICAN OPTICAL CORP. 4 Nov., 1969 [23 Jan., 1969], No. 53942/69. Heading H4R. [Also in Division G1] Noise on a signal from an electrocardiograph is detected, and if the noise exceeds a predetermined level the frequency response of the amplifier is changed. As described Fig. 9 the signal at the output of a D.C. amplifier 38 feeding a chart recorder with the signals from an ecg. is fed to a comparator which detects excursions of the signal beyond 'the recording limits of the chart recorder, due to very low frequency interference signals, and switches an additional resistor 43 in parallel with the input resistance of the D.C. amplifier, so as to limit the l.f. response of the system and allow the recorder to continue recording. The comparator and switch circuit, Fig. 10, comprises a pair of transistors 52, 53, normally non-conductive one or other of which is turned on to make the respective F.E.T. 58; 59, conductive and connect resistor 43, Fig. 9, into circuit when the input signal exceeds respectively a positive or a negative threshold value. In an alternative embodiment high frequency noise, such as impulsive interference, is detected and causes the switching in of a capacitor in parallel with the D.C. amplifier input to reduce the high frequency response of the amplifier. The two circuits, may be connected in series via an emitter follower, Fig. 12 (not shown), to deal with both types of interference. |
