Method of and an apparatus for tunable passive-gain equalization

Abstract

A passive positive-gain equalizer comprises a ferrite (100, 300) electromagnetically coupled to a single conductor (111, 311) of a digital signal defined in the frequency domain by a plurality of frequencies. Although it has no external power source other than the digital signal, the equalizer amplifies some of the signal's frequencies. In one embodiment, the equalizer (100) comprises a 'C'-shaped body portion (101) whose legs (103, 104) extend through holes in a PC board (110) to be spanned by an 'I'-shaped body portion (102). A tunnel (106) formed thereby surrounds a stripline (111) and the PC board portion (112) which carries the stripline. In another embodiment, the equalizer (300) comprises an 'E'-shaped body portion (301) whose legs (303-305) extend through holes in a PC board (310) to be spanned by an 'I'-shaped body portion (302). A pair of tunnels (306, 307) is formed thereby, and the stripline (311, 511) loops through each of the tunnels one or more times. The equalizer is tunable over a range of frequencies by varying the length or the number of the tunnels, by varying the number of loops the stripline makes through the tunnels, or by varying the number of the equalizers (300, 311) that are cascaded in series on the stripline (1211). Performance is improved by coupling a ferrite choke (800) in series with the stripline (111, 311) at the final output of the digital signal from the equalizer.