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Equalizer Circuit

IP.com Disclosure Number: IPCOM000073829D
Original Publication Date: 1971-Feb-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Hoffman, CR: AUTHOR

Abstract

In equalizer circuits to compensate for the distortion introduced into a signal over a transmission line, an all-pass network is frequently used. One such all-pass network is shown and since the output thereof varies in accordance with a second-order function of the input, it is termed a second-order all-pass filter. The filter comprises an operational amplifier 1 with the complementary (+) terminal receiving a fraction RA/(RA+RB) of the input signal since it is connected to the junction of resistors 2 and 3 across the signal input. A resistor 4(R1) and capacitor 5(C1) in series connect the signal input to the other (-) terminal of amplifier 1 with a resistor 6(R2) and a capacitor 7(C2) providing a feedback of the output signal.

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Equalizer Circuit

In equalizer circuits to compensate for the distortion introduced into a signal over a transmission line, an all-pass network is frequently used. One such all- pass network is shown and since the output thereof varies in accordance with a second-order function of the input, it is termed a second-order all-pass filter. The filter comprises an operational amplifier 1 with the complementary (+) terminal receiving a fraction RA/(RA+RB) of the input signal since it is connected to the junction of resistors 2 and 3 across the signal input. A resistor 4(R1) and capacitor 5(C1) in series connect the signal input to the other (-) terminal of amplifier 1 with a resistor 6(R2) and a capacitor 7(C2) providing a feedback of the output signal. Resistor 6 is connected from the output of amplifier 1 to its other input and capacitor 7 connects the output to the junction of resistor 4 and capacitor 5.

The quality of this circuit is largely dependent upon a term R2 times RB times C1/R1 times RA times(C1+C2). To maintain the characteristics of the allpass filter close to the design center, it is necessary to maintain close tolerances on the individual components. In the usual case where C1 and C2 are of the same order of magnitude, this results in a required use of 1% tolerance on both resistors and capacitors. The effect of the tolerance range of the capacitors used may be so greatly reduced that the much less expensive 5% or 10% tolerance capacitors can be used w...