System and method for transmit timing precompensation for a serial transmission communication channel
View Patent ↗An improved method and apparatus for transmitting digital signals in a communications channel by compensating for distortions due to attenuation of high frequency components suffered by the digital signals. In a preferred embodiment, the digital signals are pulses and the compensation is performed at the transmitter without the need for an emphasis driver, by widening the pulses to compensate for the distortion in the channel that results in narrowing of the pulses incurred in the channel. The resulting pulse train is pre-compensated for the distortions caused by the communications channel. The amount of pre-compensation can be determined statically or dynamically.
1. A Transmit Timing Precompensation circuit for digital signals transmitted in a communications channel, comprising:
a transmit timing precompensation (TTP) circuit, said TTP circuit configured for receiving a plurality of digital pulse signals in a pulse train, each of said digital pulses having an original width;
a programmable delay operatively connected to said TTP circuit, said programmable delay configured for providing information to said TTP circuit to selectively widen said digital pulses;
a pattern detector receiving said digital pulse signals prior to said pulses being received by said TTP circuit, said pattern detector operatively connected to said programmable delay and said TTP circuit, said pattern detector configured for inspecting several consecutive pulses in said digital signal pulse train and providing said TTP circuit with information to adjust the timing of said TTP circuit via said programmable delay; and
a transmit driver receiving said digital signals from said TTP circuit and transmitting said digital signals over a communications channel;
wherein said TTP circuit selectively widen only digital pulses having original widths narrower than a width determined by said pattern detector upon inspecting several consecutive pulses.
2. The apparatus of claim 1 , further comprising:
means for measuring the channel characteristics of the communication channel over which the TIP circuit transmits said pulse train;
said programmable delay programmed by said means for measuring the channel characteristics.
3. The apparatus of claim 1 , wherein said transmit timing precompensation (TIP) circuit is used with a channel that is an electro-optical channel.
4. The apparatus of claim 1 , wherein:
said TTP circuit comprises a Retiming Flip-Flop having a data input line and a clock signal input line.
5. The apparatus of claim 4 , wherein:
said Retiming Flip-Flop receiving said digital pulses in said data input line, and a clock signal in said clock signal input line, and said TTP circuit further comprises said programmable delay connected to said clock signal input line of said Retiming Flip-Flop.
6. The apparatus of claim 5 , wherein:
said pattern detector detecting several consecutive pulses in said digital signal pulse train and providing information for adjusting the timing of said Retiming Flip-Flop via said clock signal input line.
7. A method for Transmit Timing Precompensation (TTP) using a TTP circuit in a communication channel receiving a digital pulse train, the communication channel having channel characteristics of transfer function H(s) and attenuating high frequency signals, comprising the steps of:
determining the channel characteristics of said communication channel:
precompensating a digital signal to be transmitted in the communication channel by phase encoding according to the channel characteristics of said communication channel;
wherein the step of phase encoding comprises changing the digital signal by changing the spectral energy of the signal, said change in the spectral energy of the signal selected from the group consisting of selectively changing the frequency of the pulse data, selectively changing the phase of the pulse data, or selectively changing the period of the pulse data;
wherein said digital signal comprises a plurality of pulses forming pulse data, said pulses having high frequency components distorted by the communication channel, and wherein precompensating the digital signal comprises changing the digital signal by selectively widening only the pulses in said pulse data having original pulse widths narrower than a width determined based on the channel characteristics: and,
transmitting said precompensated digital signal.
8. The method according to claim lift 7 , further comprising:
using said transmit timing precompensation (TTP) circuit with a channel that is an electro-optical channel.
9. The method according to claim 7 , wherein:
the step of changing the digital signal by selectively widening the pulse width of the pulses in said pulse data comprises using programmable delay, said programmable delay input into the clock line of a flip-flop used for said selective widening of said pulses.
10. The method according to claim 7 , further comprising the step of:
detecting the pattern of the pulse data prior to precompensation, and selectively widening the pulses according to the pattern detected.
11. The method according to claim 10 , further comprising the step of:
determining the channel characteristics of said communication channel, prior to the step of phase encoding, and selectively widening said pulse data to be precompensated by phase encoding according to the channel characteristics of said communication channel.
12. The method according to claim 11 , wherein:
said step of selectively widening said pulse data is by widening all of the pulses in said pulse data by a predetermined amount according to the determined channel characteristics of said communication channel.
13. The method according to claim 11 , wherein:
said step of selectively widening said pulse data is by selectively widening some of the pulses in said pulse data by a predetermined amount determined after a predetermined number of consecutive pulses are transmitted, and after determining said channel characteristics of said communication channel in response to the predetermined number of consecutive pulses being transmitted.
14. Transmit Timing Precompensation for digital signals transmitted in a communications channel, comprising:
means for precompensating a plurality of digital pulse signals in a pulse train, said digital pulses having a first width; said precompensation means selectively widening said digital pulses from said first width to a second width and outputting said pulses in a pulse train;
programmable means for delay connected to said precompensation means, said programmable delay means providing information for said precompensation means to selectively widen said digital pulses; and
means for transmitting said digital signals received from said precompensation means over a communications channel;
wherein said means for precompensating said plurality of digital pulse signals in said pulse train selectively widen only digital pulses having first widths narrower than a width provided by said programmable means for delay.