公开(公告)号：DE1466720A1

公开(公告)日：1969-02-13

申请号：DE1466720

申请日：1964-11-03

Applicant: IBM

Inventor： DAVID PRICER WILBUR

IPC: G01R23/00 ,  H03G5/16 ,  H03G5/22

Abstract: 1,079,937. Fundamental frequency extractor. INTERNATIONAL BUSINESS MACHINES CORPORATION. Nov. 23, 1964 [Dec. 9, 1963], No. 47511/64. Headings H3T and H4R. The amplitude of the fundamental frequency component of a complex periodic electrical signal is increased in relation to the amplitudes of the higher frequency components by feeding the signal to a negative feedback amplifier having a filter which attenuates different frequencies of the signal increasingly with increasing frequency, the feedback means being arranged to feed back a control signal representative of the average value of the alternating component of the ampli. fier output signal. A variable attenuator 12 (Fig. 1) adjusts the level of an input signal applied to terminal 10 in accordance with the voltage appearing on a feedback conductor 13. The attenuator output is applied through a wide band amplifier 14 to a low-pass filter 16 which exhibits an attenuation of 6 db. per octave. The fundamental frequency of the input signal falls within the negative slope portion of the filter 16 so that the second and higher harmonics are attenuated more than the fundamental. The feedback network includes an amplitude detector 20. Several such circuits are preferably connected in series, Fig. 3 (not shown). Attenuator 12 comprises anode-to-anode connected diodes (60, 62), Fig. 5 (not shown), the output of the amplitude detector 20 being connected to the common anode connection. The amplifier 14 comprises three transistors (64, 66, 68). A resistor (70) and capacitor (72) serve as the filter 16 and are inserted in the amplifier circuit 14. The feedback network includes a D.C. isolating capacitor (73) and a transistor (74) biased to act as a rectifier. The rectified output at the collector of transistor (74) is applied across an R.C. smoothing network. In an alternative arrangement anode-to-anode connected diodes (80, 82), Fig. 6 (not shown), act as a variable attenuator and, together with a capacitor (84), act as a lowpass filter having a negative slope characteristic.