Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
1998-02-25
2001-01-09
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
C341S070000
Reexamination Certificate
active
06172634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to improvements in analog finite impulse response (FIR) based line-drivers, and more particularly to advantageous aspects of an analog-FIR-based filter embedded in a line-driver, by which wave-shaping, filtering and pre-equalization for the data stream are implemented.
2. Description of the Prior Art
According to the international standard ISO/IEC 8802-3 (ANSI/IEEE std 802-3, clause 14.3.1.2.1), any harmonics of a transmitted signal for an all-ones Manchester (return-to-zero) encoded signal have to be at least 27 dB below the fundamental, which in a 10 Base-T system is 10 MHz. For a 5 MHz signal (periodic “10” or “01” binary data), the high-frequency components of the signal have to be enhanced, thus increasing the transmission distance. This is typically called “pre-equalization.” The amount of the pre-equalization should be such that the eye-diagram of the signal at the output of the twisted-pair model (ISO 8802.3) stays inside the voltage template shown in FIG. 14-9 of ISO 8802-3. In addition, it is required that the signal amplitude for a 100 &OHgr; resistive load stay between 2.2 V to 2.8 V (i.e., 2.5 V±12%).
FIG. 1
shows a known configuration, in which the preceding requirements are met by a four-pin driver requiring four off-chip resistors and a differential off-chip filter (ATT1MX10 data sheet, August 1997). It is possible to integrate the transmit filters onto the chip by using continuous-time techniques, such as a Gm-C filter technique. However, the cut-off frequencies of continuous-time filters move from their desired value due to process and temperature conditions. To maintain the cut-off frequency of the continuous-time filter, a process plus temperature tuning mechanism has to be employed. Furthermore, designing a continuous-time filter to accommodate a large output swing (5 V peak-to-peak±12%) with a power supply of 5 V±10% is very difficult and expensive. In addition, to accommodate the pre-equalization, a second parallel continuous-time filter is required, or at least the input-stage of the filter has to be replicated. This has the disadvantage of increasing the power consumption of the driver.
SUMMARY OF THE INVENTION
The present invention integrates an analog finite impulse response (FIR) filter and a pre-equalization function for high-speed data communication. These functions are advantageously embedded within a line driver.
In a preferred embodiment, the line-driver receives as an input a Manchester-encoded digital data signal, which is then converted into an analog signal by a wave-shaping circuit. The wave-shaping circuit comprises a bank of current sources with a combined output, each current source being actuated by a switch controlled by a switching signal. The current sources are each scaled by a coefficient, and are actuated in a selected sequence during each input data pulse, thereby generating as a combined output a staircase pulse signal with n steps for each input data pulse.
REFERENCES:
patent: 3543009 (1970-11-01), Voelcker, Jr.
patent: 5267269 (1993-11-01), Shih et al.
patent: 5651029 (1997-07-01), Yang et al.
patent: 5771237 (1998-06-01), Kao
patent: 5995555 (1999-11-01), Young
patent: 0 673 139 A2 (1995-09-01), None
Lucent Technologies Microelectronics Group “ATT1MX10 (Spinnaker) Quad MAC and Transceivers” Data Sheet, pp. 45-47, Aug. 1997.
Su et al., ACMOS oversampling D/A coverter with a current mode semi-digital reconstruction filter, IEEE International Solid State Circuits Conference, 1993, Feb. 24-26, 1993, Digest of Technical Papers pp. 230-231.*
Leonowich Robert H.
Shoaei Omid
Shoval Ayal
Law Offices of Peter H. Priest, PLLC
Lucent Technologies - Inc.
Williams Howard L.
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