De-emphasizing cable equalizer
View Patent ↗In accordance with the teachings described herein, an extended equalizer circuit is provided for equalizing a digital communication signal transmitted over a transmission medium that causes a frequency-dependent attenuation of the digital communication signal. An equalizer may be used that includes a linear equalization circuit and a non-linear equalization circuit, the linear equalization circuit being configured to apply a linear filter to the digital communication signal to compensate for the frequency-dependent attenuation caused by a first portion of the transmission medium, and the non-linear equalization circuit being configured to apply one or more non-linear operations to the digital communication signal. A de-emphasizing equalizer circuit may be coupled in series between the transmission medium and the equalizer and configured to apply an additional linear filter to the digital communication signal in order to compensate for the frequency-dependent attenuation caused by a second portion of the transmission medium.
1. An extended equalizer circuit for equalizing a digital communication signal transmitted over a transmission medium, the transmission medium causing a frequency-dependent attenuation of the digital communication signal, comprising:
an equalizer that includes a linear equalization circuit and a non-linear equalization circuit, the linear equalization circuit being configured to apply a linear filter to the digital communication signal to compensate for the frequency-dependent attenuation caused by a first portion of the transmission medium and the non-linear equalization circuit being configured to apply one or more non-linear operations to the digital communication signal, wherein the first portion of the transmission medium includes up to a maximum length that the equalizer is configured to equalize; and
a de-emphasizing equalizer circuit coupled in series between the transmission medium and the equalizer, the de-emphasizing equalizer circuit being analog equalizer circuit that is configured to apply an additional linear filter to the digital communication signal in order to compensate for the frequency-dependent attenuation caused by a second portion of the transmission medium, wherein the de-emphasizing equalizer circuit applies no non-linear operations to the digital communication signal, and wherein the second portion of the transmission medium includes a length of the transmission medium beyond the maximum length that the equalizer is configured to equalize.
2. The extended equalizer circuit of claim 1 , wherein the linear filter and the additional linear filter are high-pass filters having a combined frequency response that substantially matches an inverse response of the transmission medium.
3. The extended equalizer circuit of claim 2 , wherein the additional linear filter is a first order high-pass filter.
4. The extended equalizer circuit of claim 3 , wherein the first order high-pass filter is configured to match an input impedance and an output impedance of the de-emphasizing equalizer circuit.
5. The extended equalizer circuit of claim 1 , wherein the de-emphasizing equalizer circuit further includes a flat-gain amplifier configured to amplify an output of the additional linear filter.
6. The extended equalizer circuit of claim 1 , wherein the transmission medium is a coaxial cable in a serial digital interface (SDI) link and the equalizer is a SMPTE-compliant SDI equalizer.
7. The extended equalizer circuit of claim 1 , wherein the one or more non-linear operations include at least one of DC-restoration and internal signal slicing.
8. The extended equalizer circuit of claim 1 , further comprising:
one or more additional de-emphasizing equalizer circuits coupled in series between the transmission medium and the equalizer, the one or more additional de-emphasizing circuits being configured to compensate for frequency-dependent attenuation caused by one or more additional portions of the transmission medium.
9. A method for extending a serial digital interface (SDI) equalizer to equalize greater cable lengths, comprising:
configuring the SDI equalizer to apply a linear filter to compensate for frequency-dependent attenuation in a digital communication signal caused by a first portion of a transmission cable, wherein the first portion of the transmission cable includes up to a maximum length that the SDI equalizer is configured to equalize, and wherein the SDI equalizer is further configured to apply one or more non-linear operations to the digital communication signal; and
coupling an analog de-emphasizing filter in series between the transmission cable and the SDI equalizer, the analog de-emphasizing filter being configured apply an additional linear filter to compensate for frequency-dependent attenuation in the digital communication signal caused by a second portion of the transmission cable, wherein the de-emphasizing filter does not perform any non-linear operations to the digital communication signal, and wherein the second portion of the transmission cable includes a length of the transmission cable beyond the maximum length that the equalizer is configured to equalize.
10. The method of claim 9 , further comprising:
coupling a flat-gain amplifier between the de-emphasizing filter and the SDI equalizer to compensate for flat attenuation to the digital communication signal caused by at least the de-emphasizing filter.
11. The method of claim 9 , further comprising:
coupling one or more additional de-emphasizing filters in series between the transmission cable and the SDI equalizer, the one or more additional de-emphasizing filters being configured to compensate for frequency-dependent attenuation in the digital communication signal caused by one or more additional portions of the transmission cable.