High speed data link with transmitter equalization and receiver equalization
View Patent ↗A high speed data link includes transmitter equalization and (passive) receiver equalization to compensate for frequency distortion of the data link. In one embodiment, the transmitter equalization is performed with a de-emphasis circuit. The transmitter de-emphasis circuit pre-distorts an input signal to compensate for at least some of the frequency distortion in the data caused by the transmission line. The (passive) receive equalization circuit further compensates for the frequency distortion at the output of the transmission line to flatten the amplitude response of the output signal, and thereby reduce inter-symbol interference, improve media reach and improve the bit error rate (BER).
1. A data link system configured to operate with a differential transmission line having a differential input and a differential output, the data link system comprising:
a transmitter de-emphasis circuit coupled to said input of said differential transmission line, said transmitter de-emphasis circuit including,
a first transconductance device having a fixed gain;
a second transconductance device, coupled in parallel with said first transconductance device, and having a variable gain; and
a summer device for summing current outputs of said first and second transconductance devices; and
an equalizer coupled to said differential output of said differential transmission line, said equalizer having an inductor connected between first and second transmission lines forming said differential transmission line.
2. The data link system of claim 1 , wherein said transmitter de-emphasis circuit pre-distorts said differential transmission line input to compensate for frequency distortion caused by said differential transmission line.
3. The data link system of claim 1 , wherein said transmitter de-emphasis circuit has a gain that increases with frequency across a frequency band of interest.
4. The data link system of claim 1 , wherein a signal loss of said differential transmission line increases with frequency, and wherein said transmitter de-emphasis circuit has a gain that increases with frequency to offset said signal loss of said differential transmission line.
5. The data link system of claim 1 , wherein said equalizer is a passive equalizer.
6. The data link system of claim 1 , wherein said transmitter de-emphasis circuit reduces an amplitude of low frequency components in an input signal.
7. The data link system of claim 1 , wherein said differential transmission line is one of a coaxial cable, an optical fiber, and a twisted pair.
8. The data link system of claim 1 , wherein said equalizer includes a resistor connected in-series with said inductor between said first and second transmission lines forming said differential transmission line.
9. The data link system of claim 1 , wherein said equalizer is a filter network having a nearly constant impedance.
10. The data link system of claim 1 , wherein said equalizer is a RC filter.
11. The data link system of claim 10 , wherein said RC filter has a highpass response.
12. The data link system of claim 10 , wherein said RC filter has a nearly constant input impedance.